core: always write all options in theme files

Theme files saved with /theme save and automatic backups now always
contain every themable option (full snapshot), so a theme file is
self-contained and round-trips exactly regardless of the current
configuration. The diff-only mode and the "-full" argument of
/theme save are removed.

CHANGELOG.md

@@ -12,9 +12,17 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 - core: add condition on connected relay api clients in default value of option weechat.look.hotlist_add_conditions
 - core: add `/mute` in default command for key `Alt`+`=` (toggle filters)
+- relay/api: add field "last_read_line_id" in GET /api/buffers
 
 ### Added
 
+- core: add `/theme` command with subcommands `list`, `apply`, `reset`, `save`, `rename`, `delete`, `info`, automatic backup of current themable options before apply, and built-in "light" theme
+- core: detect terminal background on first start and automatically apply the built-in "light" theme when a light terminal is detected
+- core: add `themable` flag on configuration options (auto-set for color options; explicit opt-in for string options containing `${color:...}` references via the `type|themable` syntax)
+- core: add option weechat.look.theme (informational, set by `/theme apply`)
+- core: add option weechat.look.theme_backup (boolean, default `on`)
+- api: add function `theme_register` (available to plugins and to all script languages)
+- fset: add filter `t:themable` (matches every themable option regardless of type)
 - relay: add option relay.network.unix_socket_permissions ([#2317](https://github.com/weechat/weechat/issues/2317))
 
 ### Fixed
@@ -24,10 +32,15 @@ SPDX-License-Identifier: GPL-3.0-or-later
 - irc: fix tag in message with list of names when joining a channel
 - fset: remove error displayed in core buffer when clicking with the mouse below the last option displayed
 - irc: limit size of data received from the server to prevent memory exhaustion
+- irc: fix out-of-bounds read on incoming DCC command with a quoted filename ending the message ([#2322](https://github.com/weechat/weechat/issues/2322))
 - relay: limit size of decompressed websocket frame with permessage-deflate to prevent memory exhaustion ([GHSA-v2v4-45wm-5cr3](https://github.com/weechat/weechat/security/advisories/GHSA-v2v4-45wm-5cr3))
 - relay: limit size of received websocket frame and HTTP body to prevent memory exhaustion
+- relay: limit size of partial message received while reading an HTTP request to prevent memory exhaustion
 - relay: fix timing attack on password authentication ([GHSA-vhv8-g2r9-cwcc](https://github.com/weechat/weechat/security/advisories/GHSA-vhv8-g2r9-cwcc))
+- relay: fix out-of-bounds read in dump of data ([#2324](https://github.com/weechat/weechat/issues/2324))
 - api, relay: fix timing attack on TOTP validation ([GHSA-vhv8-g2r9-cwcc](https://github.com/weechat/weechat/security/advisories/GHSA-vhv8-g2r9-cwcc))
+- xfer: replace directory separator in remote nick by underscore in download filename to prevent writing the file outside the download directory ([#2321](https://github.com/weechat/weechat/issues/2321))
+- xfer: fix out-of-bounds read when receiving empty line in DCC chat ([#2323](https://github.com/weechat/weechat/issues/2323))
 
 ## Version 4.9.1 (2026-05-31)
 

doc/CMakeLists.txt

@@ -30,7 +30,7 @@ if(ENABLE_MAN OR ENABLE_DOC)
   set(SCRIPTING_LANG de en fr it ja pl sr)
   set(FAQ_LANG de en es fr it ja pl sr)
   set(QUICKSTART_LANG cs de en es fr it ja pl ru sr)
-  set(RELAY_API_LANG en fr)
+  set(RELAY_API_LANG en fr sr)
   set(RELAY_WEECHAT_LANG en fr ja sr)
   set(DEV_LANG en fr ja sr)
 

doc/de/weechat_user.de.adoc

@@ -2197,6 +2197,152 @@ Um der Vordergrundfarbe des Terminals das Attribut "fett" zuzuordnen:
 /set weechat.color.status_time *99999
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Themen
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

doc/en/weechat_plugin_api.en.adoc

@@ -9627,6 +9627,89 @@ elif rc == weechat.WEECHAT_CONFIG_OPTION_UNSET_ERROR:
     # ...
 ----
 
+[[themes]]
+=== Themes
+
+Functions to contribute color (and other themable option) overrides to
+built-in themes. See the
+link:weechat_user.en.html#themes[user's guide / Themes] section for the
+end-user side and the `+/theme+` command.
+
+==== theme_register
+
+_WeeChat ≥ 4.10.0._
+
+Register a contribution of option overrides under a named theme. The
+caller's plugin is the owner of the contribution; subsequent calls
+with the same theme name from the same plugin merge into the existing
+contribution (later keys win for duplicates).
+
+When the calling plugin is unloaded, all its contributions are
+automatically dropped from every theme.
+
+Prototype:
+
+[source,c]
+----
+struct t_theme *weechat_theme_register (const char *name,
+                                        struct t_hashtable *overrides);
+----
+
+Arguments:
+
+* _name_: theme name (for example `+light+` or a custom name)
+* _overrides_: hashtable mapping full option names
+  (e.g. `+irc.color.input_nick+`) to their string values; the caller
+  retains ownership and may free the hashtable right after the call
+
+Return value:
+
+* pointer to the registered theme (existing or newly created), NULL on
+  error
+
+C example:
+
+[source,c]
+----
+struct t_hashtable *overrides = weechat_hashtable_new (
+    8,
+    WEECHAT_HASHTABLE_STRING,
+    WEECHAT_HASHTABLE_STRING,
+    NULL, NULL);
+if (overrides)
+{
+    weechat_hashtable_set (overrides, "irc.color.input_nick", "cyan");
+    weechat_hashtable_set (overrides, "irc.color.topic_old",  "darkgray");
+    weechat_theme_register ("light", overrides);
+    weechat_hashtable_free (overrides);
+}
+----
+
+Script (Python):
+
+[source,python]
+----
+# prototype
+def theme_register(name: str, overrides: Dict[str, str]) -> str: ...
+
+# example
+weechat.theme_register("light", {
+    "irc.color.input_nick": "cyan",
+    "irc.color.topic_old": "darkgray",
+})
+----
+
+[NOTE]
+Only options that have the _themable_ flag will be set by `/theme apply`.
+All `*.color.*` options are themable by default; string options that
+hold `+${color:...}+` references are explicitly opted in. Entries
+targeting non-themable options are silently skipped at apply-time with
+a warning logged to the _core_ buffer.
+
+[NOTE]
+When called from a script, the contribution is automatically dropped
+when the script unloads (no manual cleanup is needed).
+
 [[key_bindings]]
 === Key bindings
 

doc/en/weechat_relay_api.en.adoc

@@ -541,7 +541,8 @@ HTTP/1.1 200 OK
             "plugin": "core",
             "name": "weechat"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823423765,
@@ -571,7 +572,8 @@ HTTP/1.1 200 OK
             "tls_version": "TLS1.3",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823649069,
@@ -599,7 +601,8 @@ HTTP/1.1 200 OK
             "nick": "alice",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     }
 ]
 ----
@@ -655,7 +658,8 @@ HTTP/1.1 200 OK
             "message": "Plugins loaded: alias, buflist, charset, exec, fifo, fset, guile, irc, javascript, logger, lua, perl, php, python, relay, ruby, script, spell, tcl, trigger, typing, xfer",
             "tags": []
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 
@@ -702,6 +706,7 @@ HTTP/1.1 200 OK
         "host": "~alice@example.com"
     },
     "keys": [],
+    "last_read_line_id": -1,
     "nicklist_root": {
         "id": 0,
         "parent_group_id": -1,
@@ -900,7 +905,8 @@ HTTP/1.1 200 OK
             "key": "up",
             "command": "/fset -up"
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 

doc/en/weechat_user.en.adoc

@@ -2185,6 +2185,151 @@ Example of bold with terminal foreground color:
 /set weechat.color.status_time *99999
 ----
 
+[[themes]]
+=== Themes
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

doc/fr/weechat_plugin_api.fr.adoc

@@ -9771,6 +9771,95 @@ elif rc == weechat.WEECHAT_CONFIG_OPTION_UNSET_ERROR:
     # ...
 ----
 
+[[themes]]
+=== Thèmes
+
+Fonctions permettant de contribuer des surcharges d'options de couleur
+(et autres options modifiables par un thème) à des thèmes intégrés.
+Voir la section
+link:weechat_user.fr.html#themes[guide utilisateur / Thèmes] pour le
+côté utilisateur final et la commande `+/theme+`.
+
+==== theme_register
+
+_WeeChat ≥ 4.10.0._
+
+Enregistrer une contribution de surcharges d'options sous un thème
+nommé. L'extension appelante est le propriétaire de la contribution ;
+les appels suivants avec le même nom de thème depuis la même extension
+sont fusionnés dans la contribution existante (en cas de doublons, les
+dernières clés gagnent).
+
+Lorsque l'extension appelante est déchargée, toutes ses contributions
+sont automatiquement retirées de tous les thèmes.
+
+Prototype :
+
+[source,c]
+----
+struct t_theme *weechat_theme_register (const char *name,
+                                        struct t_hashtable *overrides);
+----
+
+Paramètres :
+
+* _name_ : nom du thème (par exemple `+light+` ou un nom personnalisé)
+* _overrides_ : table de hachage associant des noms d'options complets
+  (par exemple `+irc.color.input_nick+`) à leurs valeurs chaîne ;
+  l'appelant en conserve la propriété et peut la libérer juste après
+  l'appel
+
+Valeur de retour :
+
+* pointeur vers le thème enregistré (existant ou nouvellement créé),
+  NULL en cas d'erreur
+
+Exemple en C :
+
+[source,c]
+----
+struct t_hashtable *overrides = weechat_hashtable_new (
+    8,
+    WEECHAT_HASHTABLE_STRING,
+    WEECHAT_HASHTABLE_STRING,
+    NULL, NULL);
+if (overrides)
+{
+    weechat_hashtable_set (overrides, "irc.color.input_nick", "cyan");
+    weechat_hashtable_set (overrides, "irc.color.topic_old",  "darkgray");
+    weechat_theme_register ("light", overrides);
+    weechat_hashtable_free (overrides);
+}
+----
+
+Script (Python) :
+
+[source,python]
+----
+# prototype
+def theme_register(name: str, overrides: Dict[str, str]) -> str: ...
+
+# exemple
+weechat.theme_register("light", {
+    "irc.color.input_nick": "cyan",
+    "irc.color.topic_old": "darkgray",
+})
+----
+
+[NOTE]
+Seules les options possédant le flag _themable_ seront modifiées par
+`/theme apply`. Toutes les options `*.color.*` sont modifiables par
+défaut ; les options de type chaîne contenant des références
+`+${color:...}+` sont explicitement déclarées comme modifiables. Les
+entrées ciblant des options non modifiables sont silencieusement
+ignorées au moment de l'application avec un avertissement écrit sur
+le tampon _core_.
+
+[NOTE]
+Lorsqu'elle est appelée depuis un script, la contribution est
+automatiquement retirée lorsque le script est déchargé (aucun nettoyage
+manuel n'est nécessaire).
+
 [[key_bindings]]
 === Associations de touches
 

doc/fr/weechat_relay_api.fr.adoc

@@ -551,7 +551,8 @@ HTTP/1.1 200 OK
             "plugin": "core",
             "name": "weechat"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823423765,
@@ -580,7 +581,8 @@ HTTP/1.1 200 OK
             "tls_version": "TLS1.3",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823649069,
@@ -607,7 +609,8 @@ HTTP/1.1 200 OK
             "nick": "alice",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     }
 ]
 ----
@@ -663,7 +666,8 @@ HTTP/1.1 200 OK
             "message": "Plugins loaded: alias, buflist, charset, exec, fifo, fset, guile, irc, javascript, logger, lua, perl, php, python, relay, ruby, script, spell, tcl, trigger, typing, xfer",
             "tags": []
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 
@@ -709,6 +713,7 @@ HTTP/1.1 200 OK
         "host": "~alice@example.com"
     },
     "keys": [],
+    "last_read_line_id": -1,
     "nicklist_root": {
         "id": 0,
         "parent_group_id": -1,
@@ -906,7 +911,8 @@ HTTP/1.1 200 OK
             "key": "up",
             "command": "/fset -up"
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 

doc/fr/weechat_user.fr.adoc

@@ -2227,6 +2227,166 @@ Exemple de gras avec la couleur de texte du terminal :
 /set weechat.color.status_time *99999
 ----
 
+[[themes]]
+=== Thèmes
+
+Un thème est un ensemble nommé de surcharges d'options qui peut être
+appliqué par la commande <<command_weechat_theme,/theme>>. WeeChat est
+livré avec un thème intégré `"light"` adapté aux terminaux à fond clair
+et permet de charger temporairement des thèmes utilisateur depuis des
+fichiers.
+
+[[themes_themable_options]]
+==== Options modifiables par un thème
+
+Les thèmes ne peuvent modifier que les options marquées comme
+_themable_ (modifiables par un thème). Toutes les options `*.color.*`
+le sont par défaut ; certaines options de type chaîne contenant des
+références `+${color:...}+` (par exemple
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` ou les
+formats `+buflist.format.*+`) sont explicitement déclarées comme
+modifiables.
+
+La liste complète des options modifiables peut être affichée depuis le
+tampon <<command_fset_fset,/fset>> avec le filtre `+t:themable+`.
+
+[[themes_apply]]
+==== Appliquer un thème
+
+Pour basculer vers le thème intégré pour fond clair :
+
+----
+/theme apply light
+----
+
+L'état actuel de toutes les options modifiables est sauvegardé au
+préalable dans un fichier de sauvegarde nommé
+`+backup-AAAAMMJJ-HHMMSS-uuuuuu+` dans le répertoire `+themes+` du
+répertoire de configuration de WeeChat. L'apparence précédente peut
+ainsi être restaurée à tout moment avec :
+
+----
+/theme apply backup-AAAAMMJJ-HHMMSS-uuuuuu
+----
+
+La création de la sauvegarde peut être désactivée (déconseillé) :
+
+----
+/set weechat.look.theme_backup off
+----
+
+Si la sauvegarde est activée et que le fichier ne peut pas être écrit,
+l'application est annulée avant qu'aucune option ne soit modifiée.
+
+Le nom du dernier thème appliqué est conservé dans
+`+weechat.look.theme+` (à titre informatif uniquement ; il n'est pas
+ré-appliqué au démarrage).
+
+[[themes_reset]]
+==== Réinitialiser aux valeurs par défaut
+
+Pour rétablir l'apparence d'origine livrée avec WeeChat, réinitialiser
+toutes les options modifiables à leur valeur par défaut :
+
+----
+/theme reset
+----
+
+Une sauvegarde est écrite au préalable (même garde-fou que
+`+/theme apply+`) ; si la sauvegarde échoue, la réinitialisation est
+annulée avant qu'aucune option ne soit modifiée. L'option
+`+weechat.look.theme+` est également remise à vide.
+
+[[themes_save_delete]]
+==== Sauvegarder et supprimer des thèmes utilisateur
+
+Sauvegarder l'état actuel des options modifiables en tant que nouveau
+thème utilisateur :
+
+----
+/theme save monTheme
+----
+
+Toutes les options modifiables sont écrites, donc le fichier est
+autonome et applique exactement le même aspect sur n'importe quel
+WeeChat, quelle que soit sa configuration actuelle.
+
+Les noms réservés (noms de thèmes intégrés comme `+light+` et tout nom
+commençant par `+backup-+`) sont refusés. Les fichiers sont placés
+dans `+${weechat_config_dir}/themes/<nom>.theme+`.
+
+Renommer un thème utilisateur (usage typique : conserver une
+sauvegarde automatique utile sous un nom plus parlant) :
+
+----
+/theme rename backup-20260525-094210-123456 maSauvegarde
+----
+
+Les thèmes intégrés n'ont pas de fichier et ne peuvent pas être
+renommés ; le nom cible ne peut pas correspondre à un nom intégré ni
+commencer par `+backup-+`, et le fichier cible ne doit pas déjà
+exister. Le champ `+name+` de la section `+[info]+` à l'intérieur du
+fichier est réécrit afin que `/theme info` affiche le nouveau nom de
+manière cohérente.
+
+Supprimer un thème utilisateur :
+
+----
+/theme delete monTheme
+----
+
+Cela supprime le fichier sur le disque ; les thèmes intégrés ne
+peuvent pas être supprimés.
+
+[[themes_file_format]]
+==== Format du fichier de thème
+
+Un fichier de thème est de type INI avec deux sections :
+
+----
+[info]
+name = "solarized_light"
+description = "Thème fond clair inspiré de Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` est une section de métadonnées informatives affichées par
+`/theme info`. `+[options]+` contient les surcharges réelles ; les clés
+sont les noms complets d'options tels qu'affichés par `/set`. Les
+valeurs de type chaîne peuvent être encadrées par des guillemets
+simples ou doubles ; les guillemets sont retirés à l'analyse. Les
+options non modifiables par un thème listées dans un fichier sont
+refusées au moment de l'application et signalées sur le tampon _core_
+(ainsi, un fichier `.theme` importé depuis une source non fiable ne
+peut pas écraser des mots de passe, des listes d'auto-chargement ou
+des commandes de démarrage).
+
+Les fichiers de thème utilisateur ne sont jamais mis en cache : à
+chaque `/theme apply <nom>`, le fichier est analysé, appliqué, puis
+libéré.
+
+[[themes_resolution]]
+==== Ordre de résolution
+
+Lors de l'exécution de `+/theme apply <nom>+` :
+
+* Si `+${weechat_config_dir}/themes/<nom>.theme+` existe, le fichier
+  est analysé et utilisé (il masque tout thème intégré du même nom).
+* Sinon, le registre des thèmes intégrés est consulté ; les thèmes
+  intégrés sont enregistrés par programmation par le cœur, les
+  extensions et les scripts (voir la documentation des extensions et
+  des scripts pour `+weechat_theme_register+`).
+
+Si aucune des deux sources ne fournit le nom, l'application est
+refusée.
+
 [[charset]]
 === Charset
 

doc/it/weechat_plugin_api.it.adoc

@@ -9967,6 +9967,90 @@ elif rc == weechat.WEECHAT_CONFIG_OPTION_UNSET_ERROR:
     # ...
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Themes
+
+Functions to contribute color (and other themable option) overrides to
+built-in themes. See the
+link:weechat_user.it.html#themes[user's guide / Themes] section for the
+end-user side and the `+/theme+` command.
+
+==== theme_register
+
+_WeeChat ≥ 4.10.0._
+
+Register a contribution of option overrides under a named theme. The
+caller's plugin is the owner of the contribution; subsequent calls
+with the same theme name from the same plugin merge into the existing
+contribution (later keys win for duplicates).
+
+When the calling plugin is unloaded, all its contributions are
+automatically dropped from every theme.
+
+Prototype:
+
+[source,c]
+----
+struct t_theme *weechat_theme_register (const char *name,
+                                        struct t_hashtable *overrides);
+----
+
+Arguments:
+
+* _name_: theme name (for example `+light+` or a custom name)
+* _overrides_: hashtable mapping full option names
+  (e.g. `+irc.color.input_nick+`) to their string values; the caller
+  retains ownership and may free the hashtable right after the call
+
+Return value:
+
+* pointer to the registered theme (existing or newly created), NULL on
+  error
+
+C example:
+
+[source,c]
+----
+struct t_hashtable *overrides = weechat_hashtable_new (
+    8,
+    WEECHAT_HASHTABLE_STRING,
+    WEECHAT_HASHTABLE_STRING,
+    NULL, NULL);
+if (overrides)
+{
+    weechat_hashtable_set (overrides, "irc.color.input_nick", "cyan");
+    weechat_hashtable_set (overrides, "irc.color.topic_old",  "darkgray");
+    weechat_theme_register ("light", overrides);
+    weechat_hashtable_free (overrides);
+}
+----
+
+Script (Python):
+
+[source,python]
+----
+# prototype
+def theme_register(name: str, overrides: Dict[str, str]) -> str: ...
+
+# example
+weechat.theme_register("light", {
+    "irc.color.input_nick": "cyan",
+    "irc.color.topic_old": "darkgray",
+})
+----
+
+[NOTE]
+Only options that have the _themable_ flag will be set by `/theme apply`.
+All `*.color.*` options are themable by default; string options that
+hold `+${color:...}+` references are explicitly opted in. Entries
+targeting non-themable options are silently skipped at apply-time with
+a warning logged to the _core_ buffer.
+
+[NOTE]
+When called from a script, the contribution is automatically dropped
+when the script unloads (no manual cleanup is needed).
+
 [[key_bindings]]
 === Combinazione tasti
 

doc/it/weechat_user.it.adoc

@@ -2439,6 +2439,152 @@ Esempio di grassetto con il colore di primo piano del terminale:
 /set weechat.color.status_time *99999
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Themes
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

doc/ja/weechat_plugin_api.ja.adoc

@@ -9746,6 +9746,90 @@ elif rc == weechat.WEECHAT_CONFIG_OPTION_UNSET_ERROR:
     # ...
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Themes
+
+Functions to contribute color (and other themable option) overrides to
+built-in themes. See the
+link:weechat_user.ja.html#themes[user's guide / Themes] section for the
+end-user side and the `+/theme+` command.
+
+==== theme_register
+
+_WeeChat ≥ 4.10.0._
+
+Register a contribution of option overrides under a named theme. The
+caller's plugin is the owner of the contribution; subsequent calls
+with the same theme name from the same plugin merge into the existing
+contribution (later keys win for duplicates).
+
+When the calling plugin is unloaded, all its contributions are
+automatically dropped from every theme.
+
+Prototype:
+
+[source,c]
+----
+struct t_theme *weechat_theme_register (const char *name,
+                                        struct t_hashtable *overrides);
+----
+
+Arguments:
+
+* _name_: theme name (for example `+light+` or a custom name)
+* _overrides_: hashtable mapping full option names
+  (e.g. `+irc.color.input_nick+`) to their string values; the caller
+  retains ownership and may free the hashtable right after the call
+
+Return value:
+
+* pointer to the registered theme (existing or newly created), NULL on
+  error
+
+C example:
+
+[source,c]
+----
+struct t_hashtable *overrides = weechat_hashtable_new (
+    8,
+    WEECHAT_HASHTABLE_STRING,
+    WEECHAT_HASHTABLE_STRING,
+    NULL, NULL);
+if (overrides)
+{
+    weechat_hashtable_set (overrides, "irc.color.input_nick", "cyan");
+    weechat_hashtable_set (overrides, "irc.color.topic_old",  "darkgray");
+    weechat_theme_register ("light", overrides);
+    weechat_hashtable_free (overrides);
+}
+----
+
+Script (Python):
+
+[source,python]
+----
+# prototype
+def theme_register(name: str, overrides: Dict[str, str]) -> str: ...
+
+# example
+weechat.theme_register("light", {
+    "irc.color.input_nick": "cyan",
+    "irc.color.topic_old": "darkgray",
+})
+----
+
+[NOTE]
+Only options that have the _themable_ flag will be set by `/theme apply`.
+All `*.color.*` options are themable by default; string options that
+hold `+${color:...}+` references are explicitly opted in. Entries
+targeting non-themable options are silently skipped at apply-time with
+a warning logged to the _core_ buffer.
+
+[NOTE]
+When called from a script, the contribution is automatically dropped
+when the script unloads (no manual cleanup is needed).
+
 [[key_bindings]]
 === キー割り当て
 

doc/ja/weechat_user.ja.adoc

@@ -2375,6 +2375,152 @@ WeeChat は画面に色が表示された時点で色ペアを動的に割り当
 /set weechat.color.status_time *99999
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Themes
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

doc/pl/weechat_user.pl.adoc

@@ -2191,6 +2191,152 @@ Przykład pogrubienia z domyślnym kolorem terminala:
 /set weechat.color.status_time *99999
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Motywy
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

doc/sr/weechat_plugin_api.sr.adoc

@@ -9436,6 +9436,90 @@ elif rc == weechat.WEECHAT_CONFIG_OPTION_UNSET_ERROR:
     # ...
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Теме
+
+Functions to contribute color (and other themable option) overrides to
+built-in themes. See the
+link:weechat_user.sr.html#themes[user's guide / Themes] section for the
+end-user side and the `+/theme+` command.
+
+==== theme_register
+
+_WeeChat ≥ 4.10.0._
+
+Register a contribution of option overrides under a named theme. The
+caller's plugin is the owner of the contribution; subsequent calls
+with the same theme name from the same plugin merge into the existing
+contribution (later keys win for duplicates).
+
+When the calling plugin is unloaded, all its contributions are
+automatically dropped from every theme.
+
+Prototype:
+
+[source,c]
+----
+struct t_theme *weechat_theme_register (const char *name,
+                                        struct t_hashtable *overrides);
+----
+
+Arguments:
+
+* _name_: theme name (for example `+light+` or a custom name)
+* _overrides_: hashtable mapping full option names
+  (e.g. `+irc.color.input_nick+`) to their string values; the caller
+  retains ownership and may free the hashtable right after the call
+
+Return value:
+
+* pointer to the registered theme (existing or newly created), NULL on
+  error
+
+C example:
+
+[source,c]
+----
+struct t_hashtable *overrides = weechat_hashtable_new (
+    8,
+    WEECHAT_HASHTABLE_STRING,
+    WEECHAT_HASHTABLE_STRING,
+    NULL, NULL);
+if (overrides)
+{
+    weechat_hashtable_set (overrides, "irc.color.input_nick", "cyan");
+    weechat_hashtable_set (overrides, "irc.color.topic_old",  "darkgray");
+    weechat_theme_register ("light", overrides);
+    weechat_hashtable_free (overrides);
+}
+----
+
+Script (Python):
+
+[source,python]
+----
+# prototype
+def theme_register(name: str, overrides: Dict[str, str]) -> str: ...
+
+# example
+weechat.theme_register("light", {
+    "irc.color.input_nick": "cyan",
+    "irc.color.topic_old": "darkgray",
+})
+----
+
+[NOTE]
+Only options that have the _themable_ flag will be set by `/theme apply`.
+All `*.color.*` options are themable by default; string options that
+hold `+${color:...}+` references are explicitly opted in. Entries
+targeting non-themable options are silently skipped at apply-time with
+a warning logged to the _core_ buffer.
+
+[NOTE]
+When called from a script, the contribution is automatically dropped
+when the script unloads (no manual cleanup is needed).
+
 [[key_bindings]]
 === Тастерске пречице
 

doc/sr/weechat_relay_api.sr.adoc

@@ -543,7 +543,8 @@ HTTP/1.1 200 OK
             "plugin": "core",
             "name": "weechat"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823423765,
@@ -573,7 +574,8 @@ HTTP/1.1 200 OK
             "tls_version": "TLS1.3",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     },
     {
         "id": 1709932823649069,
@@ -601,7 +603,8 @@ HTTP/1.1 200 OK
             "nick": "alice",
             "host": "~alice@example.com"
         },
-        "keys": []
+        "keys": [],
+        "last_read_line_id": -1
     }
 ]
 ----
@@ -657,7 +660,8 @@ HTTP/1.1 200 OK
             "message": "Учитани додаци: alias, buflist, charset, exec, fifo, fset, guile, irc, javascript, logger, lua, perl, php, python, relay, ruby, script, spell, tcl, trigger, typing, xfer",
             "tags": []
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 
@@ -704,6 +708,7 @@ HTTP/1.1 200 OK
         "host": "~alice@example.com"
     },
     "keys": [],
+    "last_read_line_id": -1,
     "nicklist_root": {
         "id": 0,
         "parent_group_id": -1,
@@ -902,7 +907,8 @@ HTTP/1.1 200 OK
             "key": "up",
             "command": "/fset -up"
         }
-    ]
+    ],
+    "last_read_line_id": -1
 }
 ----
 

doc/sr/weechat_user.sr.adoc

@@ -2093,6 +2093,152 @@ include::{autogendir}/autogen_user_options.sr.adoc[tag=fset_options]
 /set weechat.color.status_time *99999
 ----
 
+// TRANSLATION MISSING
+[[themes]]
+=== Теме
+
+A theme is a named bundle of option overrides that can be applied with
+the <<command_weechat_theme,/theme>> command. WeeChat ships a built-in
+`"light"` theme tuned for light-background terminals and supports
+user-defined themes loaded transiently from files.
+
+[[themes_themable_options]]
+==== Themable options
+
+Themes can only set options marked as _themable_. All `*.color.*`
+options are themable by default; a few string options that hold format
+expressions with `+${color:...}+` references (such as
+`+weechat.color.chat_nick_colors+`, `+weechat.look.prefix_error+` or the
+`+buflist.format.*+` formats) are explicitly opted in.
+
+You can list the full themable surface area from the
+<<command_fset_fset,/fset>> buffer with the `+t:themable+` filter.
+
+[[themes_apply]]
+==== Applying a theme
+
+To switch to the built-in light-background theme:
+
+----
+/theme apply light
+----
+
+The current state of every themable option is saved beforehand to a
+backup theme file named like `+backup-YYYYMMDD-HHMMSS-uuuuuu+` in
+directory `+themes+` inside the WeeChat configuration directory, so the
+previous look can be restored at any time with:
+
+----
+/theme apply backup-YYYYMMDD-HHMMSS-uuuuuu
+----
+
+Backup creation can be disabled (not recommended):
+
+----
+/set weechat.look.theme_backup off
+----
+
+If backup is enabled and the backup file cannot be written, the apply
+is aborted before any option is changed.
+
+The name of the last applied theme is stored in
+`+weechat.look.theme+` (informational only; not re-applied at startup).
+
+[[themes_reset]]
+==== Resetting to defaults
+
+To restore the look shipped with WeeChat, reset every themable option
+to its default value:
+
+----
+/theme reset
+----
+
+A backup is written first (same gate as `+/theme apply+`); on backup
+failure the reset is aborted before any option is changed.
+`+weechat.look.theme+` is cleared too.
+
+[[themes_save_delete]]
+==== Saving and deleting user themes
+
+Save the current themable options as a new user theme file:
+
+----
+/theme save mytheme
+----
+
+Every themable option is written, so the file is self-contained and
+applies the exact same look on any WeeChat, regardless of its current
+configuration.
+
+Reserved names (built-in theme names like `+light+` and any name
+starting with `+backup-+`) are refused. Files live at
+`+${weechat_config_dir}/themes/<name>.theme+`.
+
+Rename a user theme (typical use: keep a useful automatic backup
+under a meaningful name):
+
+----
+/theme rename backup-20260525-094210-123456 mybackup
+----
+
+Built-in themes have no file and cannot be renamed; the target name
+cannot match a built-in name or start with `+backup-+`, and the
+target file must not already exist. The `+[info]+` `+name+` field
+inside the file is rewritten so `/theme info` reports the new name
+consistently.
+
+Delete a user theme:
+
+----
+/theme delete mytheme
+----
+
+This removes the file on disk; built-in themes cannot be deleted.
+
+[[themes_file_format]]
+==== Theme file format
+
+A theme file is INI-like with two sections:
+
+----
+[info]
+name = "solarized_light"
+description = "Light-background theme inspired by Solarized"
+date = "2026-05-25 09:42:10"
+weechat = "4.10.0-dev"
+
+[options]
+weechat.color.chat = "darkgray"
+weechat.color.separator = "blue"
+irc.color.input_nick = "magenta"
+buflist.format.number = "${color:28}${number}${if:${number_displayed}?.: }"
+----
+
+`+[info]+` is informational metadata shown by `/theme info`. `+[options]+`
+holds the actual overrides; keys are the full option names that would
+appear in `/set`. String values can be enclosed in double or single
+quotes; quotes are stripped at parse time. Non-themable options listed
+in a theme file are refused at apply time and logged to the core
+buffer (so a `.theme` file imported from an untrusted source cannot
+overwrite passwords, autoload lists, or startup commands).
+
+User theme files are never cached: on every `/theme apply <name>` the
+file is parsed, applied, and freed.
+
+[[themes_resolution]]
+==== Resolution order
+
+When `+/theme apply <name>+` is run:
+
+* If `+${weechat_config_dir}/themes/<name>.theme+` exists, the file
+  is parsed and used (it shadows any built-in with the same name).
+* Otherwise the built-in theme registry is consulted; built-ins are
+  registered programmatically by core, plugins and scripts (see the
+  plugin and scripting documentation for `+weechat_theme_register+`).
+
+If neither source provides the name, the apply is refused.
+
 [[charset]]
 === Charset
 

src/core/CMakeLists.txt

@@ -51,6 +51,8 @@ set(LIB_CORE_SRC
   core-signal.c core-signal.h
   core-string.c core-string.h
   core-sys.c core-sys.h
+  core-theme.c core-theme.h
+  core-theme-builtin.c
   core-upgrade.c core-upgrade.h
   core-upgrade-file.c core-upgrade-file.h
   core-url.c core-url.h

src/core/core-command.c

@@ -68,6 +68,7 @@
 #include "core-signal.h"
 #include "core-string.h"
 #include "core-sys.h"
+#include "core-theme.h"
 #include "core-upgrade.h"
 #include "core-url.h"
 #include "core-utf8.h"
@@ -7180,6 +7181,250 @@ COMMAND_CALLBACK(sys)
     COMMAND_ERROR;
 }
 
+/*
+ * Callback for "dir_exec_on_files": collects names of files matching
+ * "*.theme" into an arraylist passed as data; "backup-*.theme" is
+ * excluded when *(int *)data->show_backups is zero.
+ *
+ * The arraylist is iterated outside this callback so all dirent
+ * processing can happen in one place.
+ */
+
+struct t_command_theme_dir_collect
+{
+    struct t_arraylist *names;            /* arraylist of char * (owned)     */
+    int show_backups;                     /* include backup-*.theme ?        */
+};
+
+void
+command_theme_collect_file_cb (void *data, const char *filename)
+{
+    struct t_command_theme_dir_collect *ctx;
+    const char *base;
+    char *name;
+    size_t len;
+
+    ctx = (struct t_command_theme_dir_collect *)data;
+    base = strrchr (filename, '/');
+    base = (base) ? base + 1 : filename;
+    len = strlen (base);
+    if ((len < 7) || (strcmp (base + len - 6, ".theme") != 0))
+        return;
+    if (!ctx->show_backups && (strncmp (base, "backup-", 7) == 0))
+        return;
+    name = string_strndup (base, len - 6);
+    if (name)
+        arraylist_add (ctx->names, name);
+}
+
+int
+command_theme_strcmp_cb (void *data, struct t_arraylist *arraylist,
+                         void *pointer1, void *pointer2)
+{
+    /* make C compiler happy */
+    (void) data;
+    (void) arraylist;
+
+    return strcmp ((const char *)pointer1, (const char *)pointer2);
+}
+
+/*
+ * Callback for command "/theme": list or display details on themes.
+ */
+
+COMMAND_CALLBACK(theme)
+{
+    struct t_arraylist *list, *file_names;
+    struct t_command_theme_dir_collect collect;
+    struct t_theme *ptr_theme, *file_theme;
+    const char *ptr_active, *ptr_name;
+    char *path, *dir;
+    int i, size, show_backups;
+
+    /* make C compiler happy */
+    (void) pointer;
+    (void) data;
+    (void) buffer;
+    (void) argv_eol;
+
+    /* "/theme" or "/theme list [-backups]": list themes */
+    if ((argc == 1) || (string_strcmp (argv[1], "list") == 0))
+    {
+        show_backups = ((argc >= 3)
+                        && (string_strcmp (argv[2], "-backups") == 0));
+        ptr_active = CONFIG_STRING(config_look_theme);
+
+        list = theme_list ();
+
+        /* scan ${weechat_config_dir}/themes/ for *.theme files */
+        file_names = arraylist_new (8, 1, 0,
+                                    &command_theme_strcmp_cb, NULL,
+                                    NULL, NULL);
+        if (file_names)
+        {
+            dir = NULL;
+            string_asprintf (&dir, "%s/themes", weechat_config_dir);
+            if (dir)
+            {
+                collect.names = file_names;
+                collect.show_backups = show_backups;
+                dir_exec_on_files (dir, 0, 0,
+                                   &command_theme_collect_file_cb,
+                                   &collect);
+                free (dir);
+            }
+        }
+
+        if ((!list || (arraylist_size (list) == 0))
+            && (!file_names || (arraylist_size (file_names) == 0)))
+        {
+            gui_chat_printf (NULL, _("No theme available"));
+            arraylist_free (list);
+            arraylist_free (file_names);
+            return WEECHAT_RC_OK;
+        }
+
+        gui_chat_printf (NULL, "");
+        gui_chat_printf (NULL, _("Themes:"));
+        size = (list) ? arraylist_size (list) : 0;
+        for (i = 0; i < size; i++)
+        {
+            ptr_theme = (struct t_theme *)arraylist_get (list, i);
+            gui_chat_printf (
+                NULL,
+                "  %s %s%s%s%s%s",
+                (ptr_active && (strcmp (ptr_active, ptr_theme->name) == 0))
+                    ? "->" : "  ",
+                GUI_COLOR(GUI_COLOR_CHAT_BUFFER),
+                ptr_theme->name,
+                GUI_COLOR(GUI_COLOR_CHAT_DELIMITERS),
+                (ptr_theme->description && ptr_theme->description[0])
+                    ? ": " : "",
+                (ptr_theme->description) ? ptr_theme->description : "");
+        }
+        size = (file_names) ? arraylist_size (file_names) : 0;
+        for (i = 0; i < size; i++)
+        {
+            ptr_name = (const char *)arraylist_get (file_names, i);
+            gui_chat_printf (
+                NULL,
+                "  %s %s%s%s (file)",
+                (ptr_active && (strcmp (ptr_active, ptr_name) == 0))
+                    ? "->" : "  ",
+                GUI_COLOR(GUI_COLOR_CHAT_BUFFER),
+                ptr_name,
+                GUI_COLOR(GUI_COLOR_CHAT));
+        }
+        if (file_names)
+        {
+            size = arraylist_size (file_names);
+            for (i = 0; i < size; i++)
+                free (arraylist_get (file_names, i));
+            arraylist_free (file_names);
+        }
+        arraylist_free (list);
+        return WEECHAT_RC_OK;
+    }
+
+    /* "/theme apply <name>": apply a theme */
+    if (string_strcmp (argv[1], "apply") == 0)
+    {
+        COMMAND_MIN_ARGS(3, "apply");
+        return theme_apply (argv[2]);
+    }
+
+    /* "/theme reset": reset every themable option to its default value */
+    if (string_strcmp (argv[1], "reset") == 0)
+    {
+        return theme_reset ();
+    }
+
+    /* "/theme save <name>": write a user theme file */
+    if (string_strcmp (argv[1], "save") == 0)
+    {
+        COMMAND_MIN_ARGS(3, "save");
+        return theme_save (argv[2]);
+    }
+
+    /* "/theme rename <old> <new>": rename a user theme file */
+    if (string_strcmp (argv[1], "rename") == 0)
+    {
+        COMMAND_MIN_ARGS(4, "rename");
+        return theme_rename (argv[2], argv[3]);
+    }
+
+    /* "/theme delete <name>": remove a user theme file */
+    if (string_strcmp (argv[1], "delete") == 0)
+    {
+        COMMAND_MIN_ARGS(3, "delete");
+        return theme_delete (argv[2]);
+    }
+
+    /* "/theme info <name>": show details about a theme */
+    if (string_strcmp (argv[1], "info") == 0)
+    {
+        COMMAND_MIN_ARGS(3, "info");
+        /* file shadows registry: try user file first */
+        path = theme_user_file_path (argv[2]);
+        file_theme = NULL;
+        if (path && (access (path, R_OK) == 0))
+            file_theme = theme_file_parse (path);
+        if (!file_theme)
+        {
+            free (path);
+            path = NULL;
+            ptr_theme = theme_search (argv[2]);
+            if (!ptr_theme)
+            {
+                gui_chat_printf (NULL,
+                                 _("%sTheme \"%s\" not found"),
+                                 gui_chat_prefix[GUI_CHAT_PREFIX_ERROR],
+                                 argv[2]);
+                return WEECHAT_RC_ERROR;
+            }
+        }
+        else
+        {
+            ptr_theme = file_theme;
+        }
+        gui_chat_printf (NULL, "");
+        gui_chat_printf (NULL,
+                         _("Theme \"%s%s%s\":"),
+                         GUI_COLOR(GUI_COLOR_CHAT_BUFFER),
+                         (ptr_theme->name && ptr_theme->name[0])
+                             ? ptr_theme->name : argv[2],
+                         GUI_COLOR(GUI_COLOR_CHAT));
+        if (path)
+        {
+            gui_chat_printf (NULL,
+                             _("  source         : %s"), path);
+        }
+        else
+        {
+            gui_chat_printf (NULL,
+                             _("  source         : built-in (in-memory)"));
+        }
+        gui_chat_printf (NULL,
+                         _("  description    : %s"),
+                         (ptr_theme->description) ? ptr_theme->description : "");
+        gui_chat_printf (NULL,
+                         _("  date           : %s"),
+                         (ptr_theme->date) ? ptr_theme->date : "");
+        gui_chat_printf (NULL,
+                         _("  WeeChat version: %s"),
+                         (ptr_theme->weechat_version)
+                             ? ptr_theme->weechat_version : "");
+        gui_chat_printf (NULL,
+                         _("  overrides      : %d"),
+                         theme_overrides_count (ptr_theme));
+        free (path);
+        theme_free (file_theme);
+        return WEECHAT_RC_OK;
+    }
+
+    COMMAND_ERROR;
+}
+
 /*
  * Callback for command "/toggle": toggle value of configuration option.
  */
@@ -9832,6 +10077,65 @@ command_init (void)
         " || suspend"
         " || waitpid 1|10|100|1000",
         &command_sys, NULL, NULL);
+    hook_command (
+        NULL, "theme",
+        N_("manage color themes"),
+        /* TRANSLATORS: only text between angle brackets (eg: "<name>") may be translated */
+        N_("[list [-backups]]"
+           " || apply <name>"
+           " || reset"
+           " || save <name>"
+           " || rename <old> <new>"
+           " || delete <name>"
+           " || info <name>"),
+        CMD_ARGS_DESC(
+            N_("raw[list]: list registered themes and any *.theme files in "
+               "the WeeChat configuration directory; the active theme "
+               "(matching weechat.look.theme) is marked with \"->\". By "
+               "default backup-*.theme files are hidden; pass \"-backups\" "
+               "to include them"),
+            N_("raw[apply]: apply a theme (set every themable option to the "
+               "value from the theme); if a file named <name>.theme "
+               "exists in directory \"themes\" it shadows any built-in "
+               "theme of the same name"),
+            N_("raw[reset]: reset every themable option to its default "
+               "value (restores the original look shipped with WeeChat)"),
+            N_("raw[save]: save current themable options to a file "
+               "<name>.theme in directory \"themes\"; every themable "
+               "option is written, so the file is self-contained; the "
+               "name must not match a built-in theme or start with "
+               "\"backup-\""),
+            N_("raw[rename]: rename a user theme file (typically to "
+               "give an automatic backup a meaningful name); refuses to "
+               "rename built-in themes, refuses target names matching a "
+               "built-in or starting with \"backup-\", and refuses if "
+               "the target file already exists"),
+            N_("raw[delete]: delete a user theme file (refuses to delete "
+               "built-in themes, which have no file)"),
+            N_("raw[info]: display details on a theme (name, description, "
+               "creation date, WeeChat version, number of option overrides)"),
+            N_("name: name of a theme"),
+            "",
+            N_("Themes are named bundles of color (and other themable) "
+               "option overrides. Built-in themes are registered in memory "
+               "by core/plugins/scripts; user themes are read from files "
+               "in directory \"themes\" inside the WeeChat configuration "
+               "directory."),
+            "",
+            N_("By default, /theme apply creates a backup of current "
+               "themable values in directory \"themes\" before applying "
+               "(file name: \"backup-<timestamp>.theme\"); the previous "
+               "state can be restored with: /theme apply "
+               "backup-<timestamp>. This is controlled by the option "
+               "weechat.look.theme_backup.")),
+        "list -backups"
+        " || apply %(theme_themes_all)"
+        " || reset"
+        " || save %(theme_themes_user)"
+        " || rename %(theme_themes_files)"
+        " || delete %(theme_themes_user)"
+        " || info %(theme_themes_all)",
+        &command_theme, NULL, NULL);
     hook_command (
         NULL, "toggle",
         N_("toggle value of a config option"),

src/core/core-completion.c

@@ -46,6 +46,7 @@
 #include "core-proxy.h"
 #include "core-secure.h"
 #include "core-string.h"
+#include "core-theme.h"
 #include "../gui/gui-completion.h"
 #include "../gui/gui-bar.h"
 #include "../gui/gui-bar-item.h"
@@ -1974,6 +1975,151 @@ completion_list_add_layouts_names_cb (const void *pointer, void *data,
     return WEECHAT_RC_OK;
 }
 
+/*
+ * Add filename (without ".theme" suffix) to completion list if it ends
+ * with ".theme"; skips "backup-*.theme" entries unless data is non-NULL.
+ *
+ * Callback for dir_exec_on_files; "data" carries a pair of pointers:
+ *   data[0] = struct t_gui_completion *completion (target)
+ *   data[1] = int *show_backups
+ */
+
+struct t_completion_theme_dir
+{
+    struct t_gui_completion *completion;
+    int show_backups;
+};
+
+void
+completion_theme_add_file_cb (void *data, const char *filename)
+{
+    struct t_completion_theme_dir *ctx;
+    const char *base;
+    char *name;
+    size_t len;
+
+    ctx = (struct t_completion_theme_dir *)data;
+    base = strrchr (filename, '/');
+    base = (base) ? base + 1 : filename;
+    len = strlen (base);
+    if ((len < 7) || (strcmp (base + len - 6, ".theme") != 0))
+        return;
+    if (!ctx->show_backups && (strncmp (base, "backup-", 7) == 0))
+        return;
+    name = string_strndup (base, len - 6);
+    if (!name)
+        return;
+    gui_completion_list_add (ctx->completion, name, 0, WEECHAT_LIST_POS_SORT);
+    free (name);
+}
+
+/*
+ * Add theme names to completion list: in-memory built-ins plus any
+ * "*.theme" files in <weechat_config_dir>/themes/ (including backups).
+ */
+
+int
+completion_list_add_theme_themes_all_cb (const void *pointer, void *data,
+                                         const char *completion_item,
+                                         struct t_gui_buffer *buffer,
+                                         struct t_gui_completion *completion)
+{
+    struct t_theme *ptr_theme;
+    struct t_completion_theme_dir ctx;
+    char *dir;
+
+    /* make C compiler happy */
+    (void) pointer;
+    (void) data;
+    (void) completion_item;
+    (void) buffer;
+
+    for (ptr_theme = themes; ptr_theme; ptr_theme = ptr_theme->next_theme)
+    {
+        gui_completion_list_add (completion, ptr_theme->name,
+                                 0, WEECHAT_LIST_POS_SORT);
+    }
+
+    dir = NULL;
+    string_asprintf (&dir, "%s/themes", weechat_config_dir);
+    if (dir)
+    {
+        ctx.completion = completion;
+        ctx.show_backups = 1;
+        dir_exec_on_files (dir, 0, 0, &completion_theme_add_file_cb, &ctx);
+        free (dir);
+    }
+
+    return WEECHAT_RC_OK;
+}
+
+/*
+ * Add user theme file names (excluding built-ins and backups) to the
+ * completion list; suitable for /theme save and /theme delete.
+ */
+
+int
+completion_list_add_theme_themes_user_cb (const void *pointer, void *data,
+                                          const char *completion_item,
+                                          struct t_gui_buffer *buffer,
+                                          struct t_gui_completion *completion)
+{
+    struct t_completion_theme_dir ctx;
+    char *dir;
+
+    /* make C compiler happy */
+    (void) pointer;
+    (void) data;
+    (void) completion_item;
+    (void) buffer;
+
+    dir = NULL;
+    string_asprintf (&dir, "%s/themes", weechat_config_dir);
+    if (dir)
+    {
+        ctx.completion = completion;
+        ctx.show_backups = 0;
+        dir_exec_on_files (dir, 0, 0, &completion_theme_add_file_cb, &ctx);
+        free (dir);
+    }
+
+    return WEECHAT_RC_OK;
+}
+
+/*
+ * Add every on-disk theme file (user files + backups, no built-ins)
+ * to the completion list; suitable for /theme rename which can take a
+ * backup as its source.
+ */
+
+int
+completion_list_add_theme_themes_files_cb (const void *pointer, void *data,
+                                           const char *completion_item,
+                                           struct t_gui_buffer *buffer,
+                                           struct t_gui_completion *completion)
+{
+    struct t_completion_theme_dir ctx;
+    char *dir;
+
+    /* make C compiler happy */
+    (void) pointer;
+    (void) data;
+    (void) completion_item;
+    (void) buffer;
+
+    dir = NULL;
+    string_asprintf (&dir, "%s/themes", weechat_config_dir);
+    if (dir)
+    {
+        ctx.completion = completion;
+        ctx.show_backups = 1;
+        dir_exec_on_files (dir, 0, 0, &completion_theme_add_file_cb, &ctx);
+        free (dir);
+    }
+
+    return WEECHAT_RC_OK;
+}
+
 /*
  * Add a secured data to completion list.
  */
@@ -2365,6 +2511,16 @@ completion_init (void)
     hook_completion (NULL, "layouts_names",
                      N_("names of layouts"),
                      &completion_list_add_layouts_names_cb, NULL, NULL);
+    hook_completion (NULL, "theme_themes_all",
+                     N_("names of themes (built-ins + user files + backups)"),
+                     &completion_list_add_theme_themes_all_cb, NULL, NULL);
+    hook_completion (NULL, "theme_themes_user",
+                     N_("names of user theme files (excludes built-ins and backups)"),
+                     &completion_list_add_theme_themes_user_cb, NULL, NULL);
+    hook_completion (NULL, "theme_themes_files",
+                     N_("names of theme files on disk (user files + backups, "
+                        "no built-ins)"),
+                     &completion_list_add_theme_themes_files_cb, NULL, NULL);
     hook_completion (NULL, "secured_data",
                      N_("names of secured data (file sec.conf, section data)"),
                      &completion_list_add_secured_data_cb, NULL, NULL);

src/core/core-config-file.c

@@ -648,6 +648,7 @@ config_file_option_malloc (void)
         new_option->name = NULL;
         new_option->parent_name = NULL;
         new_option->type = 0;
+        new_option->themable = 0;
         new_option->description = NULL;
         new_option->string_values = NULL;
         new_option->min = 0;
@@ -704,16 +705,37 @@ config_file_new_option (struct t_config_file *config_file,
                         void *callback_delete_data)
 {
     struct t_config_option *new_option;
-    int var_type, int_value, argc, i, index_value, number;
-    char *pos, *option_name, *parent_name;
+    int var_type, int_value, argc, i, index_value, number, themable;
+    char *pos, *option_name, *parent_name, *type_name;
+    const char *ptr_type;
 
     new_option = NULL;
     option_name = NULL;
     parent_name = NULL;
+    type_name = NULL;
+    themable = 0;
 
     if (!name || !type)
         goto error;
 
+    /*
+     * extract optional "|themable" suffix from type
+     * (e.g.: "string|themable" for a string option that contains color names)
+     */
+    pos = strchr (type, '|');
+    if (pos && (strcmp (pos, "|themable") == 0))
+    {
+        type_name = string_strndup (type, pos - type);
+        if (!type_name)
+            goto error;
+        ptr_type = type_name;
+        themable = 1;
+    }
+    else
+    {
+        ptr_type = type;
+    }
+
     pos = strstr (name, " << ");
     if (pos)
     {
@@ -734,7 +756,7 @@ config_file_new_option (struct t_config_file *config_file,
     var_type = -1;
     for (i = 0; i < CONFIG_NUM_OPTION_TYPES; i++)
     {
-        if (strcmp (type, config_option_type_string[i]) == 0)
+        if (strcmp (ptr_type, config_option_type_string[i]) == 0)
         {
             var_type = i;
             break;
@@ -744,10 +766,14 @@ config_file_new_option (struct t_config_file *config_file,
     {
         gui_chat_printf (NULL, "%sUnknown option type \"%s\"",
                          gui_chat_prefix[GUI_CHAT_PREFIX_ERROR],
-                         type);
+                         ptr_type);
         goto error;
     }
 
+    /* color options are always themable */
+    if (var_type == CONFIG_OPTION_TYPE_COLOR)
+        themable = 1;
+
     /*
      * compatibility with versions < 4.1.0: force enum type for an integer
      * with string values
@@ -784,6 +810,7 @@ config_file_new_option (struct t_config_file *config_file,
             goto error;
         new_option->parent_name = (parent_name) ? strdup (parent_name) : NULL;
         new_option->type = var_type;
+        new_option->themable = themable;
         if (description)
         {
             new_option->description = strdup (description);
@@ -969,6 +996,7 @@ error:
 end:
     free (option_name);
     free (parent_name);
+    free (type_name);
     return new_option;
 }
 
@@ -2438,6 +2466,8 @@ config_file_option_get_pointer (struct t_config_option *option,
         return option->parent_name;
     else if (strcmp (property, "type") == 0)
         return &option->type;
+    else if (strcmp (property, "themable") == 0)
+        return &option->themable;
     else if (strcmp (property, "description") == 0)
         return option->description;
     else if (strcmp (property, "string_values") == 0)
@@ -4247,6 +4277,7 @@ config_file_hdata_config_option_cb (const void *pointer, void *data,
         HDATA_VAR(struct t_config_option, name, STRING, 0, NULL, NULL);
         HDATA_VAR(struct t_config_option, parent_name, STRING, 0, NULL, NULL);
         HDATA_VAR(struct t_config_option, type, INTEGER, 0, NULL, NULL);
+        HDATA_VAR(struct t_config_option, themable, INTEGER, 0, NULL, NULL);
         HDATA_VAR(struct t_config_option, description, STRING, 0, NULL, NULL);
         HDATA_VAR(struct t_config_option, string_values, STRING, 0, "*,*", NULL);
         HDATA_VAR(struct t_config_option, min, INTEGER, 0, NULL, NULL);
@@ -4359,6 +4390,8 @@ config_file_add_option_to_infolist (struct t_infolist *infolist,
     {
         goto error;
     }
+    if (!infolist_new_var_integer (ptr_item, "themable", option->themable))
+        goto error;
     if (option->value)
     {
         value = config_file_option_value_to_string (option, 0, 0, 0);
@@ -4523,6 +4556,7 @@ config_file_print_log (void)
                 log_printf ("        name . . . . . . . . . . . . : '%s'", ptr_option->name);
                 log_printf ("        parent_name. . . . . . . . . : '%s'", ptr_option->parent_name);
                 log_printf ("        type . . . . . . . . . . . . : %d", ptr_option->type);
+                log_printf ("        themable . . . . . . . . . . : %d", ptr_option->themable);
                 log_printf ("        description. . . . . . . . . : '%s'", ptr_option->description);
                 log_printf ("        string_values. . . . . . . . : %p", ptr_option->string_values);
                 log_printf ("        min. . . . . . . . . . . . . : %d", ptr_option->min);

src/core/core-config-file.h

@@ -154,6 +154,8 @@ struct t_config_option
     char *parent_name;                     /* parent name (to inherit the   */
                                            /* value from another option)    */
     enum t_config_option_type type;        /* type                          */
+    int themable;                          /* 1 if option is themable       */
+                                           /* (color, or string with color) */
     char *description;                     /* description                   */
     char **string_values;                  /* allowed string values         */
     int min, max;                          /* min and max for value         */

src/core/core-config.c

@@ -50,6 +50,7 @@
 #include "core-proxy.h"
 #include "core-string.h"
 #include "core-sys.h"
+#include "core-theme.h"
 #include "core-util.h"
 #include "core-version.h"
 #include "../gui/gui-bar.h"
@@ -222,6 +223,8 @@ struct t_config_option *config_look_separator_horizontal = NULL;
 struct t_config_option *config_look_separator_vertical = NULL;
 struct t_config_option *config_look_tab_whitespace_char = NULL;
 struct t_config_option *config_look_tab_width = NULL;
+struct t_config_option *config_look_theme = NULL;
+struct t_config_option *config_look_theme_backup = NULL;
 struct t_config_option *config_look_time_format = NULL;
 struct t_config_option *config_look_whitespace_char = NULL;
 struct t_config_option *config_look_window_auto_zoom = NULL;
@@ -1381,7 +1384,7 @@ config_change_color (const void *pointer, void *data,
     (void) data;
     (void) option;
 
-    if (gui_init_ok)
+    if (gui_init_ok && !theme_applying)
     {
         gui_color_init_weechat ();
         gui_window_ask_refresh (1);
@@ -3446,7 +3449,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         config_look_buffer_time_format = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "buffer_time_format", "string",
+            "buffer_time_format", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("time format for each line displayed in buffers (see man "
                "strftime for date/time specifiers, extra specifiers are "
@@ -3470,7 +3473,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_buffer_time_same = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "buffer_time_same", "string",
+            "buffer_time_same", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("time displayed for a message with same time as previous message: "
                "use a space \" \" to hide time, another string to display this "
@@ -3637,7 +3640,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_day_change_message_1date = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "day_change_message_1date", "string",
+            "day_change_message_1date", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("message displayed when the day has changed, with one date "
                "displayed (for example at beginning of buffer) (see man "
@@ -3650,7 +3653,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_day_change_message_2dates = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "day_change_message_2dates", "string",
+            "day_change_message_2dates", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("message displayed when the day has changed, with two dates "
                "displayed (between two messages); the second date specifiers "
@@ -3967,7 +3970,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_item_time_format = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "item_time_format", "string",
+            "item_time_format", "string|themable",
             N_("time format for \"time\" bar item (see man strftime for "
                "date/time specifiers) (note: content is evaluated, so you can "
                "use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4022,7 +4025,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_nick_color_force = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "nick_color_force", "string",
+            "nick_color_force", "string|themable",
             N_("force color for some nicks: hash computed with nickname "
                "to find color will not be used for these nicks (format is: "
                "\"nick1:color1;nick2:color2\"); look up for nicks is with "
@@ -4114,7 +4117,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         config_look_prefix[GUI_CHAT_PREFIX_ERROR] = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "prefix_error", "string",
+            "prefix_error", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("prefix for error messages (note: content is evaluated, so you "
                "can use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4124,7 +4127,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_prefix[GUI_CHAT_PREFIX_NETWORK] = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "prefix_network", "string",
+            "prefix_network", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("prefix for network messages (note: content is evaluated, so you "
                "can use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4134,7 +4137,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_prefix[GUI_CHAT_PREFIX_ACTION] = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "prefix_action", "string",
+            "prefix_action", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("prefix for action messages (note: content is evaluated, so you "
                "can use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4144,7 +4147,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_prefix[GUI_CHAT_PREFIX_JOIN] = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "prefix_join", "string",
+            "prefix_join", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("prefix for join messages (note: content is evaluated, so you "
                "can use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4154,7 +4157,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_look_prefix[GUI_CHAT_PREFIX_QUIT] = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
-            "prefix_quit", "string",
+            "prefix_quit", "string|themable",
             /* TRANSLATORS: string "${color:xxx}" must NOT be translated */
             N_("prefix for quit messages (note: content is evaluated, so you "
                "can use colors with format \"${color:xxx}\", see /help eval)"),
@@ -4423,6 +4426,26 @@ config_weechat_init_options (void)
             NULL, NULL, NULL,
             &config_change_tab, NULL, NULL,
             NULL, NULL, NULL);
+        config_look_theme = config_file_new_option (
+            weechat_config_file, weechat_config_section_look,
+            "theme", "string",
+            N_("name of the last theme applied with command /theme "
+               "(set automatically, do not change manually); informational "
+               "only, the theme is not re-applied at startup"),
+            NULL, 0, 0, "", NULL, 0,
+            NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
+        config_look_theme_backup = config_file_new_option (
+            weechat_config_file, weechat_config_section_look,
+            "theme_backup", "boolean",
+            N_("create a backup theme file with the current themable "
+               "options before applying a theme with command /theme; if "
+               "the backup file cannot be written, the apply is aborted "
+               "(no option is changed); the backup file is written to "
+               "directory \"themes\" inside the WeeChat configuration "
+               "directory and can be restored with: /theme apply "
+               "backup-<timestamp>"),
+            NULL, 0, 0, "on", NULL, 0,
+            NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         config_look_time_format = config_file_new_option (
             weechat_config_file, weechat_config_section_look,
             "time_format", "string",
@@ -4643,7 +4666,7 @@ config_weechat_init_options (void)
             NULL, NULL, NULL);
         config_color_chat_nick_colors = config_file_new_option (
             weechat_config_file, weechat_config_section_color,
-            "chat_nick_colors", "string",
+            "chat_nick_colors", "string|themable",
             /* TRANSLATORS: please do not translate "lightred:blue" */
             N_("text color for nicks (comma separated list of colors, "
                "background is allowed with format: \"fg:bg\", for example: "
@@ -4914,7 +4937,7 @@ config_weechat_init_options (void)
         /* eval syntax highlighting colors (for "${raw_hl:xxx}" and "${hl:xxx}") */
         config_color_eval_syntax_colors = config_file_new_option (
             weechat_config_file, weechat_config_section_color,
-            "eval_syntax_colors", "string",
+            "eval_syntax_colors", "string|themable",
             /* TRANSLATORS: please do not translate "lightred:blue" */
             N_("text color for syntax highlighting in evaluated strings, "
                "with \"${raw_hl:...}\" and \"${hl:...}\" (comma separated "

src/core/core-config.h

@@ -277,6 +277,8 @@ extern struct t_config_option *config_look_separator_horizontal;
 extern struct t_config_option *config_look_separator_vertical;
 extern struct t_config_option *config_look_tab_whitespace_char;
 extern struct t_config_option *config_look_tab_width;
+extern struct t_config_option *config_look_theme;
+extern struct t_config_option *config_look_theme_backup;
 extern struct t_config_option *config_look_time_format;
 extern struct t_config_option *config_look_whitespace_char;
 extern struct t_config_option *config_look_window_auto_zoom;

src/core/core-theme-builtin.c

@@ -0,0 +1,129 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* Built-in theme registrations (core contribution only). */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "weechat.h"
+#include "core-hashtable.h"
+#include "core-theme.h"
+#include "../plugins/weechat-plugin.h"
+
+
+/*
+ * Core overrides for the "light" theme: option values tuned for a
+ * light-background terminal. Order is by full option name to keep diffs
+ * stable; the list ends with a NULL sentinel.
+ */
+
+struct t_theme_builtin_entry
+{
+    const char *option;
+    const char *value;
+};
+
+struct t_theme_builtin_entry theme_builtin_light_core[] =
+{
+    { "weechat.bar.status.color_bg",           "254"        },
+    { "weechat.bar.status.color_bg_inactive",  "default"    },
+    { "weechat.bar.title.color_bg",            "254"        },
+    { "weechat.bar.title.color_bg_inactive",   "default"    },
+    { "weechat.color.bar_more",                "magenta"    },
+    { "weechat.color.chat_buffer",             "default"    },
+    { "weechat.color.chat_channel",            "default"    },
+    { "weechat.color.chat_nick",               "cyan"       },
+    { "weechat.color.chat_nick_colors",
+      "red,green,brown,blue,magenta,cyan,lightred,lightblue,lightmagenta,"
+      "20,28,52,57,58,61,63,88,94,128,166,202" },
+    { "weechat.color.chat_nick_self",          "default"    },
+    { "weechat.color.chat_prefix_action",      "default"    },
+    { "weechat.color.chat_prefix_error",       "94"         },
+    { "weechat.color.chat_prefix_join",        "green"      },
+    { "weechat.color.chat_prefix_more",        "magenta"    },
+    { "weechat.color.chat_prefix_quit",        "red"        },
+    { "weechat.color.chat_prefix_suffix",      "251"        },
+    { "weechat.color.chat_server",             "94"         },
+    { "weechat.color.chat_text_found_bg",      "magenta"    },
+    { "weechat.color.chat_time_delimiters",    "94"         },
+    { "weechat.color.eval_syntax_colors",
+      "green,red,blue,magenta,94,cyan" },
+    { "weechat.color.input_actions",           "28"         },
+    { "weechat.color.item_away",               "brown"      },
+    { "weechat.color.separator",               "251"        },
+    { "weechat.color.status_count_msg",        "94"         },
+    { "weechat.color.status_data_highlight",   "93"         },
+    { "weechat.color.status_data_msg",         "94"         },
+    { "weechat.color.status_data_private",     "green"      },
+    { "weechat.color.status_more",             "94"         },
+    { "weechat.color.status_mouse",            "green"      },
+    { "weechat.color.status_name",             "default"    },
+    { "weechat.color.status_name_insecure",    "202"        },
+    { "weechat.color.status_name_tls",         "default"    },
+    { "weechat.color.status_number",           "28"         },
+    { NULL,                                    NULL         },
+};
+
+/*
+ * Builds a hashtable of overrides from a NULL-terminated table and
+ * registers it under the given theme name.
+ */
+
+void
+theme_builtin_register_entries (const char *name,
+                                const struct t_theme_builtin_entry *entries)
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = hashtable_new (32,
+                               WEECHAT_HASHTABLE_STRING,
+                               WEECHAT_HASHTABLE_STRING,
+                               NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i].option; i++)
+        hashtable_set (overrides, entries[i].option, entries[i].value);
+
+    theme_register (NULL, NULL, name, overrides);
+
+    hashtable_free (overrides);
+}
+
+/*
+ * Registers all built-in themes contributed by core. Called once from
+ * theme_init; plugins/scripts add their own contributions later via
+ * weechat_theme_register.
+ */
+
+void
+theme_builtin_init (void)
+{
+    theme_builtin_register_entries ("light", theme_builtin_light_core);
+}

src/core/core-theme.h

@@ -0,0 +1,92 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_THEME_H
+#define WEECHAT_THEME_H
+
+struct t_hashtable;
+struct t_arraylist;
+struct t_weechat_plugin;
+
+/*
+ * A contribution is one (owner, overrides) pair attached to a theme.
+ * "owner" is identified by a (plugin, script) pair:
+ *   - plugin == NULL && script == NULL  =>  core
+ *   - plugin != NULL && script == NULL  =>  plugin (e.g. irc, fset)
+ *   - plugin != NULL && script != NULL  =>  individual script under that
+ *                                           script-language plugin
+ */
+struct t_theme_contribution
+{
+    struct t_weechat_plugin *plugin;
+    const void *script;
+    struct t_hashtable *overrides;        /* full_option_name -> value       */
+    struct t_theme_contribution *prev_contribution;
+    struct t_theme_contribution *next_contribution;
+};
+
+struct t_theme
+{
+    char *name;                           /* "light", "solarized", ...       */
+    char *description;                    /* free-form text                  */
+    char *date;                           /* "YYYY-MM-DD HH:MM:SS"           */
+    char *weechat_version;                /* version at registration time    */
+    struct t_theme_contribution *contributions;
+    struct t_theme_contribution *last_contribution;
+    struct t_theme *prev_theme;
+    struct t_theme *next_theme;
+};
+
+extern struct t_theme *themes;
+extern struct t_theme *last_theme;
+extern int theme_applying;                /* gate for config_change_color    */
+
+extern struct t_theme *theme_search (const char *name);
+extern struct t_theme *theme_register (struct t_weechat_plugin *plugin,
+                                       const void *script,
+                                       const char *name,
+                                       struct t_hashtable *overrides);
+extern int theme_overrides_count (struct t_theme *theme);
+extern const char *theme_get_override (struct t_theme *theme,
+                                       const char *option_name);
+extern struct t_arraylist *theme_list (void);
+extern int theme_apply (const char *name);
+extern int theme_reset (void);
+extern int theme_save (const char *name);
+extern int theme_rename (const char *old_name, const char *new_name);
+extern int theme_delete (const char *name);
+extern char *theme_make_backup (void);
+extern char *theme_user_file_path (const char *name);
+extern struct t_theme *theme_file_parse (const char *path);
+extern void theme_free (struct t_theme *theme);
+
+/* lifecycle: drop all contributions owned by a plugin or script */
+extern void theme_unregister_plugin (struct t_weechat_plugin *plugin);
+extern void theme_unregister_script (struct t_weechat_plugin *plugin,
+                                     const void *script);
+
+extern void theme_init (void);
+extern void theme_end (void);
+
+/* implemented in core-theme-builtin.c */
+extern void theme_builtin_init (void);
+
+#endif /* WEECHAT_THEME_H */

src/core/weechat.c

@@ -75,6 +75,7 @@
 #include "core-secure-config.h"
 #include "core-signal.h"
 #include "core-string.h"
+#include "core-theme.h"
 #include "core-upgrade.h"
 #include "core-url.h"
 #include "core-utf8.h"
@@ -97,6 +98,7 @@ char *weechat_argv0 = NULL;            /* WeeChat binary file name (argv[0])*/
 int weechat_upgrading = 0;             /* =1 if WeeChat is upgrading        */
 int weechat_first_start = 0;           /* first start of WeeChat?           */
 time_t weechat_first_start_time = 0;   /* start time (used by /uptime cmd)  */
+int weechat_term_theme_light = 0;      /* 1 if light theme detected         */
 int weechat_upgrade_count = 0;         /* number of /upgrade done           */
 struct timeval weechat_current_start_timeval; /* start time used to display */
                                        /* duration of /upgrade              */
@@ -182,22 +184,34 @@ weechat_startup_message (void)
     if (weechat_first_start)
     {
         /* message on first run (when weechat.conf is created) */
-        gui_chat_printf (NULL, "");
+        gui_chat_printf (NULL, _("Welcome to WeeChat!"));
         gui_chat_printf (
             NULL,
-            _("Welcome to WeeChat!\n"
-              "\n"
-              "If you are discovering WeeChat, it is recommended to read at "
-              "least the quickstart guide, and the user's guide if you have "
-              "some time; they explain main WeeChat concepts.\n"
-              "All WeeChat docs are available at: https://weechat.org/doc/\n"
-              "\n"
-              "Moreover, there is inline help with /help on all commands and "
-              "options (use Tab key to complete the name).\n"
-              "The command /fset can help to customize WeeChat.\n"
-              "\n"
-              "You can add and connect to an IRC server with /server and "
+            _("If you are discovering WeeChat, it is recommended to "
+              "read at least the quickstart guide, and the user's guide if "
+              "you have some time; they explain main WeeChat concepts."));
+        gui_chat_printf (
+            NULL,
+            _("All WeeChat docs are available at: %s"),
+            WEECHAT_WEBSITE_DOC);
+        gui_chat_printf (
+            NULL,
+            _("Moreover, there is inline help with /help on all commands and "
+              "options (use Tab key to complete the name)."));
+        gui_chat_printf (
+            NULL,
+            _("The command /fset can help to customize WeeChat."));
+        gui_chat_printf (
+            NULL,
+            _("You can add and connect to an IRC server with /server and "
               "/connect commands (see /help server)."));
+        if (weechat_term_theme_light)
+        {
+            gui_chat_printf (
+                NULL,
+                _("The \"light\" theme will be automatically applied. "
+                "Use /theme reset to switch back to the default dark theme."));
+        }
         gui_chat_printf (NULL, "");
         gui_chat_printf (NULL, "---");
         gui_chat_printf (NULL, "");
@@ -368,6 +382,9 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
             * weechat_current_start_timeval.tv_usec)
            ^ getpid ());
 
+    /* detect the terminal theme, before initializing the GUI */
+    weechat_term_theme_light = gui_term_theme_is_light ();
+
     weeurl_init ();                     /* initialize URL                   */
     string_init ();                     /* initialize string                */
     signal_init ();                     /* initialize signals               */
@@ -384,6 +401,8 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
         weechat_shutdown (EXIT_FAILURE, 0);
     if (!secure_config_init ())         /* init secured data options (sec.*)*/
         weechat_shutdown (EXIT_FAILURE, 0);
+    theme_init ();                      /* initialize theme registry        */
+    theme_builtin_init ();              /* register built-in themes         */
     if (!config_weechat_init ())        /* init WeeChat options (weechat.*) */
         weechat_shutdown (EXIT_FAILURE, 0);
     args_parse (argc, argv);            /* parse command line args          */
@@ -423,6 +442,13 @@ weechat_init (int argc, char *argv[], void (*gui_init_cb)(void))
         weechat_doc_gen_ok = doc_generate (weechat_doc_gen_path);
         weechat_quit = 1;
     }
+
+    if (weechat_first_start && isatty (STDOUT_FILENO) && !weechat_headless && !weechat_doc_gen)
+    {
+        /* switch to "light" theme if terminal background was detected as "light" */
+        if (weechat_term_theme_light)
+            theme_apply ("light");
+    }
 }
 
 /*
@@ -449,6 +475,7 @@ weechat_end (void (*gui_end_cb)(int clean_exit))
     unhook_all ();                      /* remove all hooks                 */
     hdata_end ();                       /* end hdata                        */
     secure_end ();                      /* end secured data                 */
+    theme_end ();                       /* end theme registry               */
     string_end ();                      /* end string                       */
     weeurl_end ();
     weechat_shutdown (-1, 0);           /* end other things                 */

src/core/weechat.h

@@ -55,6 +55,7 @@
 
 #define WEECHAT_COPYRIGHT_DATE   "(C) 2003-2026"
 #define WEECHAT_WEBSITE          "https://weechat.org/"
+#define WEECHAT_WEBSITE_DOC      "https://weechat.org/doc/"
 #define WEECHAT_WEBSITE_DOWNLOAD "https://weechat.org/download/"
 #define WEECHAT_AUTHOR_NAME      "Sébastien Helleu"
 #define WEECHAT_AUTHOR_EMAIL     "flashcode@flashtux.org"

src/gui/curses/gui-curses-term.c

@@ -25,6 +25,14 @@
 #include "config.h"
 #endif
 
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/select.h>
+#include <sys/time.h>
+#include <termios.h>
+#include <unistd.h>
+
 #ifndef WEECHAT_HEADLESS
 #ifdef HAVE_NCURSESW_CURSES_H
 #ifdef __sun
@@ -37,6 +45,8 @@
 #endif /* HAVE_NCURSESW_CURSES_H */
 #endif /* WEECHAT_HEADLESS */
 
+#include "../../core/weechat.h"
+
 
 /*
  * Set "eat_newline_glitch" variable.
@@ -56,3 +66,139 @@ gui_term_set_eat_newline_glitch (int value)
     (void) value;
 #endif
 }
+
+/*
+ * Auto-detects the terminal background as "light" or "dark".
+ *
+ * Best-effort, in order:
+ *
+ *   1. Environment variable COLORFGBG (set by rxvt, urxvt, Konsole,
+ *      ...): "fg;bg" or "fg;default;bg"; the last ';'-separated
+ *      component is the bg ANSI color index. 0-6 + 8 are dark,
+ *      7 + 9-15 are light.
+ *
+ *   2. OSC 11 escape query on /dev/tty: write "\033]11;?\033\\",
+ *      wait up to 100 ms for a reply of the form
+ *      "...rgb:RRRR/GGGG/BBBB..." (each component is 1-4 hex digits
+ *      depending on the terminal). Classify the answer by Rec. 601
+ *      luminance computed on the high nibble of each component
+ *      (resolution is plenty for a light/dark binary decision and
+ *      avoids width-normalization headaches).
+ *
+ * /dev/tty is used rather than stdin/stdout so a pipe redirection
+ * does not defeat detection. The select() timeout caps how long a
+ * silent terminal can stall startup. Headless mode and any I/O error
+ * short-circuit to the safe default 0 (dark), which is also returned
+ * when both probes are inconclusive.
+ *
+ * MUST be called before curses init: it briefly puts the tty in raw
+ * mode and reads/writes escape sequences directly.
+ *
+ * Returns 1 if a light background is detected, otherwise 0 (0 is the
+ * preferred value when detection is unsure).
+ */
+
+int
+gui_term_theme_is_light (void)
+{
+    const char *colorfgbg, *p;
+    char *endptr;
+    long bg;
+    int fd, n, i, len;
+    struct termios old_attr, new_attr;
+    fd_set rfds;
+    struct timeval tv;
+    char buf[256], *q, *qend;
+    unsigned long comp_high[3], luminance;
+
+    if (weechat_headless)
+        return 0;
+
+    /* 1. COLORFGBG */
+    colorfgbg = getenv ("COLORFGBG");
+    if (colorfgbg && colorfgbg[0])
+    {
+        p = strrchr (colorfgbg, ';');
+        if (p)
+        {
+            bg = strtol (p + 1, &endptr, 10);
+            if (endptr != p + 1 && *endptr == '\0')
+            {
+                if (bg == 7 || (bg >= 9 && bg <= 15))
+                    return 1;
+                if ((bg >= 0 && bg <= 6) || bg == 8)
+                    return 0;
+            }
+        }
+    }
+
+    /* 2. OSC 11 query on the controlling terminal */
+    fd = open ("/dev/tty", O_RDWR | O_NOCTTY);
+    if (fd < 0)
+        return 0;
+
+    if (tcgetattr (fd, &old_attr) != 0)
+    {
+        close (fd);
+        return 0;
+    }
+    new_attr = old_attr;
+    new_attr.c_lflag &= (tcflag_t) ~(ICANON | ECHO);
+    new_attr.c_cc[VMIN] = 0;
+    new_attr.c_cc[VTIME] = 0;
+    if (tcsetattr (fd, TCSANOW, &new_attr) != 0)
+    {
+        close (fd);
+        return 0;
+    }
+
+    n = -1;
+    if (write (fd, "\033]11;?\033\\", 8) == 8)
+    {
+        FD_ZERO (&rfds);
+        FD_SET (fd, &rfds);
+        tv.tv_sec = 0;
+        tv.tv_usec = 100000;  /* 100 ms cap on terminals that won't reply */
+        if (select (fd + 1, &rfds, NULL, NULL, &tv) > 0)
+            n = read (fd, buf, sizeof (buf) - 1);
+    }
+
+    tcsetattr (fd, TCSANOW, &old_attr);
+    close (fd);
+
+    if (n <= 0)
+        return 0;
+    buf[n] = '\0';
+
+    q = strstr (buf, "rgb:");
+    if (!q)
+        return 0;
+    q += 4;
+
+    for (i = 0; i < 3; i++)
+    {
+        qend = q;
+        while ((*qend >= '0' && *qend <= '9')
+               || (*qend >= 'a' && *qend <= 'f')
+               || (*qend >= 'A' && *qend <= 'F'))
+            qend++;
+        len = (int)(qend - q);
+        if (len < 1 || len > 4)
+            return 0;
+        /* high nibble of this component: width-independent brightness */
+        comp_high[i] = strtoul (q, NULL, 16) >> ((len - 1) * 4);
+        q = qend;
+        if (i < 2)
+        {
+            if (*q != '/')
+                return 0;
+            q++;
+        }
+    }
+
+    /* Rec. 601 with coefficients summing to 1000; max = 15 * 1000 */
+    luminance = (299UL * comp_high[0]
+                 + 587UL * comp_high[1]
+                 + 114UL * comp_high[2]);
+    return (luminance > 7500) ? 1 : 0;
+}

src/gui/gui-main.h

@@ -31,5 +31,6 @@ extern void gui_main_end (int clean_exit);
 
 /* terminal functions (GUI dependent) */
 extern void gui_term_set_eat_newline_glitch (int value);
+extern int gui_term_theme_is_light (void);
 
 #endif /* WEECHAT_GUI_MAIN_H */

src/plugins/buflist/CMakeLists.txt

@@ -27,6 +27,7 @@ add_library(buflist MODULE
   buflist-config.c buflist-config.h
   buflist-info.c buflist-info.h
   buflist-mouse.c buflist-mouse.h
+  buflist-theme.c buflist-theme.h
 )
 set_target_properties(buflist PROPERTIES PREFIX "")
 

src/plugins/buflist/buflist-config.c

@@ -645,7 +645,7 @@ buflist_config_init (void)
     {
         buflist_config_format_buffer = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "buffer", "string",
+            "buffer", "string|themable",
             N_("format of each line with a buffer "
                "(note: content is evaluated, see /help buflist); "
                "example: standard format for bar item \"buflist\" and only the "
@@ -663,7 +663,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_buffer_current = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "buffer_current", "string",
+            "buffer_current", "string|themable",
             N_("format for the line with current buffer "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:,17}${format_buffer}", NULL, 0,
@@ -672,7 +672,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist", "string",
+            "hotlist", "string|themable",
             N_("format for hotlist "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0,
@@ -683,7 +683,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_level[3] = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_highlight", "string",
+            "hotlist_highlight", "string|themable",
             N_("format for a buffer with hotlist level \"highlight\" "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:magenta}", NULL, 0,
@@ -692,7 +692,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_level[0] = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_low", "string",
+            "hotlist_low", "string|themable",
             N_("format for a buffer with hotlist level \"low\" "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:white}", NULL, 0,
@@ -701,7 +701,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_level[1] = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_message", "string",
+            "hotlist_message", "string|themable",
             N_("format for a buffer with hotlist level \"message\" "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:brown}", NULL, 0,
@@ -710,7 +710,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_level_none = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_none", "string",
+            "hotlist_none", "string|themable",
             N_("format for a buffer not in hotlist "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:default}", NULL, 0,
@@ -719,7 +719,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_level[2] = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_private", "string",
+            "hotlist_private", "string|themable",
             N_("format for a buffer with hotlist level \"private\" "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:green}", NULL, 0,
@@ -728,7 +728,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_hotlist_separator = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "hotlist_separator", "string",
+            "hotlist_separator", "string|themable",
             N_("separator for counts in hotlist "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color:default},", NULL, 0,
@@ -737,7 +737,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_indent = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "indent", "string",
+            "indent", "string|themable",
             N_("string displayed to indent channel, private and list buffers "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "  ", NULL, 0,
@@ -746,7 +746,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_lag = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "lag", "string",
+            "lag", "string|themable",
             N_("format for lag on an IRC server buffer "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0,
@@ -757,7 +757,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_name = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "name", "string",
+            "name", "string|themable",
             N_("format for buffer name "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${name}", NULL, 0,
@@ -766,7 +766,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_nick_prefix = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "nick_prefix", "string",
+            "nick_prefix", "string|themable",
             N_("format for nick prefix on a channel "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0, "${color_nick_prefix}${nick_prefix}", NULL, 0,
@@ -775,7 +775,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_number = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "number", "string",
+            "number", "string|themable",
             N_("format for buffer number, ${number} is the indented number "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0,
@@ -786,7 +786,7 @@ buflist_config_init (void)
             NULL, NULL, NULL);
         buflist_config_format_tls_version = weechat_config_new_option (
             buflist_config_file, buflist_config_section_format,
-            "tls_version", "string",
+            "tls_version", "string|themable",
             N_("format for TLS version on an IRC server buffer "
                "(note: content is evaluated, see /help buflist)"),
             NULL, 0, 0,

src/plugins/buflist/buflist-theme.c

@@ -0,0 +1,93 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* buflist contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "buflist.h"
+#include "buflist-theme.h"
+
+
+/*
+ * buflist contribution to the "light" theme: format strings tuned for
+ * a light-background terminal. Each row is { option_full_name, value };
+ * the table is NULL-terminated.
+ */
+
+const char *buflist_theme_light[][2] =
+{
+    { "buflist.format.buffer_current",
+      "${color:,117}${format_buffer}" },
+    { "buflist.format.hotlist_low",
+      "${color:default}" },
+    { "buflist.format.hotlist_message",
+      "${color:94}" },
+    { "buflist.format.lag",
+      " ${color:green}[${color:94}${lag}${color:green}]" },
+    { "buflist.format.number",
+      "${color:28}${number}${if:${number_displayed}?.: }" },
+    { NULL, NULL },
+};
+
+/*
+ * Registers buflist's contribution to one theme from a NULL-terminated
+ * table of {option, value} rows.
+ */
+
+void
+buflist_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+/*
+ * Registers all built-in theme contributions from buflist.
+ */
+
+void
+buflist_theme_init (void)
+{
+    buflist_theme_register ("light", buflist_theme_light);
+}

src/plugins/buflist/buflist-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_BUFLIST_THEME_H
+#define WEECHAT_PLUGIN_BUFLIST_THEME_H
+
+extern void buflist_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_BUFLIST_THEME_H */

src/plugins/buflist/buflist.c

@@ -34,6 +34,7 @@
 #include "buflist-config.h"
 #include "buflist-info.h"
 #include "buflist-mouse.h"
+#include "buflist-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(BUFLIST_PLUGIN_NAME);
@@ -455,6 +456,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     buflist_config_read ();
 
+    buflist_theme_init ();
+
     if (!buflist_bar_item_init ())
         return WEECHAT_RC_ERROR;
 

src/plugins/exec/CMakeLists.txt

@@ -25,6 +25,7 @@ add_library(exec MODULE
   exec-command.c exec-command.h
   exec-completion.c exec-completion.h
   exec-config.c exec-config.h
+  exec-theme.c exec-theme.h
 )
 set_target_properties(exec PROPERTIES PREFIX "")
 

src/plugins/exec/exec-theme.c

@@ -0,0 +1,70 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* exec contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "exec.h"
+#include "exec-theme.h"
+
+
+const char *exec_theme_light[][2] =
+{
+    { "exec.color.flag_finished", "red" },
+    { "exec.color.flag_running",  "green" },
+    { NULL,                       NULL },
+};
+
+void
+exec_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+exec_theme_init (void)
+{
+    exec_theme_register ("light", exec_theme_light);
+}

src/plugins/exec/exec-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_EXEC_THEME_H
+#define WEECHAT_PLUGIN_EXEC_THEME_H
+
+extern void exec_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_EXEC_THEME_H */

src/plugins/exec/exec.c

@@ -32,6 +32,7 @@
 #include "exec-command.h"
 #include "exec-completion.h"
 #include "exec-config.h"
+#include "exec-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(EXEC_PLUGIN_NAME);
@@ -742,6 +743,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
     if (!exec_config_init ())
         return WEECHAT_RC_ERROR;
 
+    exec_theme_init ();
+
     exec_config_read ();
 
     /* hook some signals */

src/plugins/fset/CMakeLists.txt

@@ -29,6 +29,7 @@ add_library(fset MODULE
   fset-info.c fset-info.h
   fset-mouse.c fset-mouse.h
   fset-option.c fset-option.h
+  fset-theme.c fset-theme.h
 )
 set_target_properties(fset PROPERTIES PREFIX "")
 

src/plugins/fset/fset-command.c

@@ -702,7 +702,9 @@ fset_command_init (void)
             N_("> `xxx`: show only options with \"xxx\" in name"),
             N_("> `f:xxx`: show only configuration file \"xxx\""),
             N_("> `t:xxx`: show only type \"xxx\" (bool/int/str/col/enum "
-               "or boolean/integer/string/color/enum)"),
+               "or boolean/integer/string/color/enum); the special value "
+               "\"themable\" matches all options with the themable flag, "
+               "regardless of type"),
             N_("> `d`: show only changed options"),
             N_("> `d:xxx`: show only changed options with \"xxx\" in "
                "name"),

src/plugins/fset/fset-config.c

@@ -572,7 +572,7 @@ fset_config_init (void)
             NULL, NULL, NULL);
         fset_config_format_option[1] = weechat_config_new_option (
             fset_config_file, fset_config_section_format,
-            "option2", "string",
+            "option2", "string|themable",
             N_("second format of each line, used when option "
                "fset.look.format_number is set to 2 "
                "(note: content is evaluated, see /help fset); "

src/plugins/fset/fset-option.c

@@ -335,6 +335,10 @@ fset_option_match_filter (struct t_fset_option *fset_option, const char *filter)
     }
     else if (strncmp (filter, "t:", 2) == 0)
     {
+        /* virtual cross-type value: match themable flag (any option type) */
+        if (weechat_strcasecmp (filter + 2, "themable") == 0)
+            return (fset_option->themable) ? 1 : 0;
+
         /* filter by type */
         return (
             (weechat_strcasecmp (
@@ -426,7 +430,7 @@ fset_option_set_values (struct t_fset_option *fset_option,
     const char **ptr_string_values;
     void *ptr_default_value, *ptr_value;
     struct t_config_option *ptr_parent_option;
-    int *ptr_type, *ptr_min, *ptr_max;
+    int *ptr_type, *ptr_themable, *ptr_min, *ptr_max;
     char str_value[64], str_allowed_values[4096];
 
     /* file */
@@ -466,6 +470,10 @@ fset_option_set_values (struct t_fset_option *fset_option,
     ptr_type = weechat_config_option_get_pointer (option, "type");
     fset_option->type = *ptr_type;
 
+    /* themable */
+    ptr_themable = weechat_config_option_get_pointer (option, "themable");
+    fset_option->themable = (ptr_themable) ? *ptr_themable : 0;
+
     /* default value */
     free (fset_option->default_value);
     fset_option->default_value = NULL;
@@ -784,6 +792,7 @@ fset_option_alloc (struct t_config_option *option)
     new_fset_option->name = NULL;
     new_fset_option->parent_name = NULL;
     new_fset_option->type = 0;
+    new_fset_option->themable = 0;
     new_fset_option->default_value = NULL;
     new_fset_option->value = NULL;
     new_fset_option->parent_value = NULL;
@@ -1691,6 +1700,7 @@ fset_option_hdata_option_cb (const void *pointer, void *data,
         WEECHAT_HDATA_VAR(struct t_fset_option, name, STRING, 0, NULL, NULL);
         WEECHAT_HDATA_VAR(struct t_fset_option, parent_name, STRING, 0, NULL, NULL);
         WEECHAT_HDATA_VAR(struct t_fset_option, type, INTEGER, 0, NULL, NULL);
+        WEECHAT_HDATA_VAR(struct t_fset_option, themable, INTEGER, 0, NULL, NULL);
         WEECHAT_HDATA_VAR(struct t_fset_option, default_value, STRING, 0, NULL, NULL);
         WEECHAT_HDATA_VAR(struct t_fset_option, value, STRING, 0, NULL, NULL);
         WEECHAT_HDATA_VAR(struct t_fset_option, parent_value, STRING, 0, NULL, NULL);
@@ -1740,6 +1750,8 @@ fset_option_add_to_infolist (struct t_infolist *infolist,
         return 0;
     if (!weechat_infolist_new_var_string (ptr_item, "type_en", fset_option_type_string[fset_option->type]))
         return 0;
+    if (!weechat_infolist_new_var_integer (ptr_item, "themable", fset_option->themable))
+        return 0;
     if (!weechat_infolist_new_var_string (ptr_item, "default_value", fset_option->default_value))
         return 0;
     if (!weechat_infolist_new_var_string (ptr_item, "value", fset_option->value))
@@ -1793,6 +1805,7 @@ fset_option_print_log (void)
         weechat_log_printf ("  type. . . . . . . . . : %d ('%s')",
                             ptr_fset_option->type,
                             fset_option_type_string[ptr_fset_option->type]);
+        weechat_log_printf ("  themable. . . . . . . : %d", ptr_fset_option->themable);
         weechat_log_printf ("  default_value . . . . : '%s'", ptr_fset_option->default_value);
         weechat_log_printf ("  value . . . . . . . . : '%s'", ptr_fset_option->value);
         weechat_log_printf ("  parent_value. . . . . : '%s'", ptr_fset_option->parent_value);

src/plugins/fset/fset-option.h

@@ -46,6 +46,7 @@ struct t_fset_option
     char *name;                          /* option full name: file.sect.opt */
     char *parent_name;                   /* parent option name              */
     enum t_fset_option_type type;        /* option type                     */
+    int themable;                        /* 1 if option is themable         */
     char *default_value;                 /* option default value            */
     char *value;                         /* option value                    */
     char *parent_value;                  /* parent option value             */

src/plugins/fset/fset-theme.c

@@ -0,0 +1,130 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* fset contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "fset.h"
+#include "fset-theme.h"
+
+
+/*
+ * fset contribution to the "light" theme: option values tuned for a
+ * light-background terminal. Each row is { option_full_name, value };
+ * the table is NULL-terminated.
+ */
+
+const char *fset_theme_light[][2] =
+{
+    { "fset.color.allowed_values_selected",  "default" },
+    { "fset.color.color_name",               "darkgray" },
+    { "fset.color.color_name_selected",      "darkgray" },
+    { "fset.color.default_value_selected",   "default" },
+    { "fset.color.description_selected",     "242" },
+    { "fset.color.file_changed",             "94" },
+    { "fset.color.file_changed_selected",    "94" },
+    { "fset.color.file_selected",            "default" },
+    { "fset.color.help_default_value",       "default" },
+    { "fset.color.help_name",                "default" },
+    { "fset.color.index",                    "24" },
+    { "fset.color.index_selected",           "24" },
+    { "fset.color.line_marked_bg1",          "193" },
+    { "fset.color.line_marked_bg2",          "193" },
+    { "fset.color.line_selected_bg1",        "117" },
+    { "fset.color.line_selected_bg2",        "117" },
+    { "fset.color.marked",                   "94" },
+    { "fset.color.marked_selected",          "94" },
+    { "fset.color.max_selected",             "default" },
+    { "fset.color.min_selected",             "default" },
+    { "fset.color.name_changed",             "red" },
+    { "fset.color.name_changed_selected",    "red" },
+    { "fset.color.name_selected",            "default" },
+    { "fset.color.option_changed",           "94" },
+    { "fset.color.option_changed_selected",  "94" },
+    { "fset.color.option_selected",          "default" },
+    { "fset.color.parent_name_selected",     "default" },
+    { "fset.color.parent_value",             "24" },
+    { "fset.color.parent_value_selected",    "24" },
+    { "fset.color.quotes_changed_selected",  "default" },
+    { "fset.color.section_changed",          "94" },
+    { "fset.color.section_changed_selected", "94" },
+    { "fset.color.section_selected",         "default" },
+    { "fset.color.string_values_selected",   "default" },
+    { "fset.color.title_count_options",      "30" },
+    { "fset.color.title_current_option",     "30" },
+    { "fset.color.title_filter",             "18" },
+    { "fset.color.title_marked_options",     "94" },
+    { "fset.color.title_sort",               "darkgray" },
+    { "fset.color.type",                     "58" },
+    { "fset.color.type_selected",            "58" },
+    { "fset.color.unmarked_selected",        "default" },
+    { "fset.color.value",                    "20" },
+    { "fset.color.value_changed",            "red" },
+    { "fset.color.value_changed_selected",   "red" },
+    { "fset.color.value_selected",           "20" },
+    { "fset.color.value_undef_selected",     "magenta" },
+    { NULL,                                  NULL },
+};
+
+/*
+ * Registers fset's contribution to one theme from a NULL-terminated
+ * table of {option, value} rows.
+ */
+
+void
+fset_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+/*
+ * Registers all built-in theme contributions from fset.
+ */
+
+void
+fset_theme_init (void)
+{
+    fset_theme_register ("light", fset_theme_light);
+}

src/plugins/fset/fset-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_FSET_THEME_H
+#define WEECHAT_PLUGIN_FSET_THEME_H
+
+extern void fset_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_FSET_THEME_H */

src/plugins/fset/fset.c

@@ -35,6 +35,7 @@
 #include "fset-info.h"
 #include "fset-mouse.h"
 #include "fset-option.h"
+#include "fset-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(FSET_PLUGIN_NAME);
@@ -126,6 +127,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     fset_config_read ();
 
+    fset_theme_init ();
+
     if (!fset_bar_item_init ())
         return WEECHAT_RC_ERROR;
 

src/plugins/guile/weechat-guile-api.c

@@ -2003,6 +2003,32 @@ weechat_guile_api_config_unset_plugin (SCM option)
     API_RETURN_INT(rc);
 }
 
+SCM
+weechat_guile_api_theme_register (SCM name, SCM overrides)
+{
+    struct t_hashtable *c_overrides;
+    const char *result;
+    SCM return_value;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (!scm_is_string (name) || !scm_list_p (overrides))
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    c_overrides = weechat_guile_alist_to_hashtable (overrides,
+                                                    WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                                    WEECHAT_HASHTABLE_STRING,
+                                                    WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_guile_plugin,
+                             guile_current_script,
+                             API_SCM_TO_STRING(name), c_overrides));
+
+    weechat_hashtable_free (c_overrides);
+
+    API_RETURN_STRING(result);
+}
+
 SCM
 weechat_guile_api_key_bind (SCM context, SCM keys)
 {
@@ -5537,6 +5563,7 @@ weechat_guile_api_module_init (void *data)
     API_DEF_FUNC(config_set_plugin, 2);
     API_DEF_FUNC(config_set_desc_plugin, 2);
     API_DEF_FUNC(config_unset_plugin, 1);
+    API_DEF_FUNC(theme_register, 2);
     API_DEF_FUNC(key_bind, 2);
     API_DEF_FUNC(key_unbind, 2);
     API_DEF_FUNC(prefix, 1);

src/plugins/irc/CMakeLists.txt

@@ -48,6 +48,7 @@ add_library(irc MODULE
   irc-sasl.c irc-sasl.h
   irc-server.c irc-server.h
   irc-tag.c irc-tag.h
+  irc-theme.c irc-theme.h
   irc-typing.c irc-typing.h
   irc-upgrade.c irc-upgrade.h
 )

src/plugins/irc/irc-config.c

@@ -3959,7 +3959,7 @@ irc_config_init (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         irc_config_color_mirc_remap = weechat_config_new_option (
             irc_config_file, irc_config_section_color,
-            "mirc_remap", "string",
+            "mirc_remap", "string|themable",
             /* TRANSLATORS: please do not translate the list of WeeChat color names at the end of string */
             N_("remap mirc colors in messages using a hashtable (used only "
                "for standard colors, not RGB colors): keys are \"fg,bg\" as "
@@ -3977,7 +3977,7 @@ irc_config_init (void)
             NULL, NULL, NULL);
         irc_config_color_nick_prefixes = weechat_config_new_option (
             irc_config_file, irc_config_section_color,
-            "nick_prefixes", "string",
+            "nick_prefixes", "string|themable",
             N_("color for nick prefixes using mode char (o=op, h=halfop, "
                "v=voice, ..), format is: \"o:color1;h:color2;v:color3\" (if a "
                "mode is not found, WeeChat will try with next modes received "
@@ -4008,7 +4008,7 @@ irc_config_init (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         irc_config_color_term_remap = weechat_config_new_option (
             irc_config_file, irc_config_section_color,
-            "term_remap", "string",
+            "term_remap", "string|themable",
             N_("remap terminal color numbers in messages using a hashtable "
                "(used only for RGB colors as hexadecimal, which are first "
                "translated to terminal color numbers): keys are \"fg,bg\" as "

src/plugins/irc/irc-ctcp.c

@@ -857,7 +857,7 @@ irc_ctcp_recv_dcc (struct t_irc_protocol_ctxt *ctxt, const char *arguments)
              * double-quote
              */
             pos = strrchr (pos_file, '"');
-            if (!pos || (pos == pos_file))
+            if (!pos || (pos == pos_file) || !pos[1])
             {
                 weechat_printf (
                     ctxt->server->buffer,
@@ -1032,7 +1032,7 @@ irc_ctcp_recv_dcc (struct t_irc_protocol_ctxt *ctxt, const char *arguments)
              * double-quote
              */
             pos = strrchr (pos_file, '"');
-            if (!pos || (pos == pos_file))
+            if (!pos || (pos == pos_file) || !pos[1])
             {
                 weechat_printf (
                     ctxt->server->buffer,
@@ -1176,7 +1176,7 @@ irc_ctcp_recv_dcc (struct t_irc_protocol_ctxt *ctxt, const char *arguments)
              * double-quote
              */
             pos = strrchr (pos_file, '"');
-            if (!pos || (pos == pos_file))
+            if (!pos || (pos == pos_file) || !pos[1])
             {
                 weechat_printf (
                     ctxt->server->buffer,

src/plugins/irc/irc-theme.c

@@ -0,0 +1,93 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* IRC plugin contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "irc.h"
+#include "irc-theme.h"
+
+
+/*
+ * IRC contribution to the "light" theme: option values tuned for a
+ * light-background terminal. Each row is { option_full_name, value };
+ * the table is NULL-terminated.
+ */
+
+const char *irc_theme_light[][2] =
+{
+    { "irc.color.input_nick",                  "cyan" },
+    { "irc.color.item_lag_finished",           "94" },
+    { "irc.color.item_tls_version_deprecated", "202" },
+    { "irc.color.list_buffer_line_selected",   "default" },
+    { "irc.color.message_chghost",             "94" },
+    { "irc.color.message_setname",             "94" },
+    { "irc.color.nick_prefixes",
+      "y:red;q:red;a:cyan;o:green;h:magenta;v:94;*:blue" },
+    { "irc.color.topic_new",                   "28" },
+    { "irc.color.topic_old",                   "darkgray" },
+    { NULL,                                    NULL },
+};
+
+/*
+ * Registers IRC's contribution to one theme from a NULL-terminated
+ * table of {option, value} rows.
+ */
+
+void
+irc_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+/*
+ * Registers all built-in theme contributions from IRC.
+ */
+
+void
+irc_theme_init (void)
+{
+    irc_theme_register ("light", irc_theme_light);
+}

src/plugins/irc/irc-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_IRC_THEME_H
+#define WEECHAT_PLUGIN_IRC_THEME_H
+
+extern void irc_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_IRC_THEME_H */

src/plugins/irc/irc.c

@@ -47,6 +47,7 @@
 #include "irc-redirect.h"
 #include "irc-server.h"
 #include "irc-tag.h"
+#include "irc-theme.h"
 #include "irc-typing.h"
 #include "irc-upgrade.h"
 
@@ -217,6 +218,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     irc_config_read ();
 
+    irc_theme_init ();
+
     irc_list_init ();
 
     irc_raw_init ();

src/plugins/javascript/weechat-js-api.cpp

@@ -1898,6 +1898,31 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(rc);
 }
 
+API_FUNC(theme_register)
+{
+    struct t_hashtable *hashtable;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", "sh", API_RETURN_EMPTY);
+
+    v8::String::Utf8Value name(args[0]);
+    hashtable = weechat_js_object_to_hashtable (
+        args[1]->ToObject(),
+        WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+        WEECHAT_HASHTABLE_STRING,
+        WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_js_plugin,
+                             js_current_script,
+                             *name, hashtable));
+
+    if (hashtable)
+        weechat_hashtable_free (hashtable);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     struct t_hashtable *hashtable;
@@ -5468,6 +5493,7 @@ WeechatJsV8::loadLibs()
     API_DEF_FUNC(config_set_plugin);
     API_DEF_FUNC(config_set_desc_plugin);
     API_DEF_FUNC(config_unset_plugin);
+    API_DEF_FUNC(theme_register);
     API_DEF_FUNC(key_bind);
     API_DEF_FUNC(key_unbind);
     API_DEF_FUNC(prefix);

src/plugins/logger/CMakeLists.txt

@@ -27,6 +27,7 @@ add_library(logger MODULE
   logger-config.c logger-config.h
   logger-info.c logger-info.h
   logger-tail.c logger-tail.h
+  logger-theme.c logger-theme.h
 )
 set_target_properties(logger PROPERTIES PREFIX "")
 

src/plugins/logger/logger-theme.c

@@ -0,0 +1,70 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* logger contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "logger.h"
+#include "logger-theme.h"
+
+
+const char *logger_theme_light[][2] =
+{
+    { "logger.color.backlog_end",  "darkgray" },
+    { "logger.color.backlog_line", "darkgray" },
+    { NULL,                        NULL },
+};
+
+void
+logger_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+logger_theme_init (void)
+{
+    logger_theme_register ("light", logger_theme_light);
+}

src/plugins/logger/logger-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_LOGGER_THEME_H
+#define WEECHAT_PLUGIN_LOGGER_THEME_H
+
+extern void logger_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_LOGGER_THEME_H */

src/plugins/logger/logger.c

@@ -36,6 +36,7 @@
 #include "logger-command.h"
 #include "logger-config.h"
 #include "logger-info.h"
+#include "logger-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(LOGGER_PLUGIN_NAME);
@@ -785,6 +786,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     logger_config_read ();
 
+    logger_theme_init ();
+
     logger_command_init ();
 
     logger_buffer_start_all (1);

src/plugins/lua/weechat-lua-api.c

@@ -2081,6 +2081,32 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(rc);
 }
 
+API_FUNC(theme_register)
+{
+    const char *name;
+    struct t_hashtable *hashtable;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (lua_gettop (L) < 2)
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    name = lua_tostring (L, -2);
+    hashtable = weechat_lua_tohashtable (L, -1,
+                                         WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                         WEECHAT_HASHTABLE_STRING,
+                                         WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_lua_plugin,
+                             lua_current_script,
+                             name, hashtable));
+
+    weechat_hashtable_free (hashtable);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     const char *context;
@@ -5849,6 +5875,7 @@ const struct luaL_Reg weechat_lua_api_funcs[] = {
     API_DEF_FUNC(config_set_plugin),
     API_DEF_FUNC(config_set_desc_plugin),
     API_DEF_FUNC(config_unset_plugin),
+    API_DEF_FUNC(theme_register),
     API_DEF_FUNC(key_bind),
     API_DEF_FUNC(key_unbind),
     API_DEF_FUNC(prefix),

src/plugins/perl/weechat-perl-api.c

@@ -2000,6 +2000,33 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(rc);
 }
 
+API_FUNC(theme_register)
+{
+    char *name;
+    struct t_hashtable *hashtable;
+    const char *result;
+    dXSARGS;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (items < 2)
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    name = SvPV_nolen (ST (0));
+    hashtable = weechat_perl_hash_to_hashtable (ST (1),
+                                                WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                                WEECHAT_HASHTABLE_STRING,
+                                                WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_perl_plugin,
+                             perl_current_script,
+                             name, hashtable));
+
+    weechat_hashtable_free (hashtable);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     char *context;
@@ -5801,6 +5828,7 @@ weechat_perl_api_init (pTHX)
     API_DEF_FUNC(config_set_plugin);
     API_DEF_FUNC(config_set_desc_plugin);
     API_DEF_FUNC(config_unset_plugin);
+    API_DEF_FUNC(theme_register);
     API_DEF_FUNC(key_bind);
     API_DEF_FUNC(key_unbind);
     API_DEF_FUNC(prefix);

src/plugins/php/weechat-php-api.c

@@ -2175,6 +2175,35 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(result);
 }
 
+API_FUNC(theme_register)
+{
+    zend_string *z_name;
+    zval *z_overrides;
+    char *name;
+    struct t_hashtable *overrides;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (zend_parse_parameters (ZEND_NUM_ARGS(), "Sa", &z_name,
+                               &z_overrides) == FAILURE)
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    name = ZSTR_VAL(z_name);
+    overrides = weechat_php_array_to_hashtable (z_overrides,
+                                                WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                                WEECHAT_HASHTABLE_STRING,
+                                                WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_php_plugin,
+                             php_current_script,
+                             (const char *)name, overrides));
+
+    weechat_hashtable_free (overrides);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     zend_string *z_context;

src/plugins/php/weechat-php-api.h

@@ -132,6 +132,7 @@ PHP_FUNCTION(weechat_config_is_set_plugin);
 PHP_FUNCTION(weechat_config_set_plugin);
 PHP_FUNCTION(weechat_config_set_desc_plugin);
 PHP_FUNCTION(weechat_config_unset_plugin);
+PHP_FUNCTION(weechat_theme_register);
 PHP_FUNCTION(weechat_key_bind);
 PHP_FUNCTION(weechat_key_unbind);
 PHP_FUNCTION(weechat_prefix);

src/plugins/php/weechat-php.c

@@ -190,6 +190,7 @@ const zend_function_entry weechat_functions[] = {
     PHP_FE(weechat_config_set_plugin, arginfo_weechat_config_set_plugin)
     PHP_FE(weechat_config_set_desc_plugin, arginfo_weechat_config_set_desc_plugin)
     PHP_FE(weechat_config_unset_plugin, arginfo_weechat_config_unset_plugin)
+    PHP_FE(weechat_theme_register, arginfo_weechat_theme_register)
     PHP_FE(weechat_key_bind, arginfo_weechat_key_bind)
     PHP_FE(weechat_key_unbind, arginfo_weechat_key_unbind)
     PHP_FE(weechat_prefix, arginfo_weechat_prefix)

src/plugins/php/weechat-php_arginfo.h

@@ -233,6 +233,11 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_weechat_config_unset_plugin arginfo_weechat_charset_set
 
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_weechat_theme_register, 0, 2, IS_STRING, 0)
+	ZEND_ARG_TYPE_INFO(0, p0, IS_STRING, 0)
+	ZEND_ARG_TYPE_INFO(0, p1, IS_ARRAY, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_weechat_key_bind, 0, 2, IS_LONG, 0)
 	ZEND_ARG_TYPE_INFO(0, p0, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, p1, IS_ARRAY, 0)

src/plugins/php/weechat-php_legacy_arginfo.h

@@ -194,6 +194,8 @@ ZEND_END_ARG_INFO()
 
 #define arginfo_weechat_config_unset_plugin arginfo_weechat_plugin_get_name
 
+#define arginfo_weechat_theme_register arginfo_weechat_iconv_to_internal
+
 #define arginfo_weechat_key_bind arginfo_weechat_iconv_to_internal
 
 #define arginfo_weechat_key_unbind arginfo_weechat_iconv_to_internal

src/plugins/plugin-script-api.c

@@ -1568,6 +1568,28 @@ plugin_script_api_config_unset_plugin (struct t_weechat_plugin *weechat_plugin,
     return return_code;
 }
 
+/*
+ * Register theme overrides on behalf of a script.
+ *
+ * Forwards to weechat_plugin->theme_register with the script pointer
+ * as the owner, so the contribution can be auto-purged when the
+ * script unloads (see plugin_script_remove_themes).
+ */
+
+struct t_theme *
+plugin_script_api_theme_register (struct t_weechat_plugin *weechat_plugin,
+                                  struct t_plugin_script *script,
+                                  const char *name,
+                                  struct t_hashtable *overrides)
+{
+    if (!script)
+        return NULL;
+    return (weechat_plugin->theme_register) (weechat_plugin,
+                                             script,
+                                             name,
+                                             overrides);
+}
+
 /*
  * Create an upgrade file.
  *

src/plugins/plugin-script-api.h

@@ -438,6 +438,10 @@ extern void plugin_script_api_config_set_desc_plugin (struct t_weechat_plugin *w
 extern int plugin_script_api_config_unset_plugin (struct t_weechat_plugin *weechat_plugin,
                                                   struct t_plugin_script *script,
                                                   const char *option);
+extern struct t_theme *plugin_script_api_theme_register (struct t_weechat_plugin *weechat_plugin,
+                                                         struct t_plugin_script *script,
+                                                         const char *name,
+                                                         struct t_hashtable *overrides);
 extern struct t_upgrade_file *plugin_script_api_upgrade_new (struct t_weechat_plugin *weechat_plugin,
                                                              struct t_plugin_script *script,
                                                              const char *filename,

src/plugins/plugin-script.c

@@ -1080,6 +1080,18 @@ plugin_script_free (struct t_plugin_script *script)
     free (script);
 }
 
+/*
+ * Remove all theme contributions registered by this script.
+ */
+
+void
+plugin_script_remove_themes (struct t_weechat_plugin *weechat_plugin,
+                             struct t_plugin_script *script)
+{
+    weechat_theme_unregister_script (script);
+    (void) weechat_plugin;  /* used implicitly via the macro */
+}
+
 /*
  * Remove a script from list of scripts.
  */
@@ -1101,6 +1113,8 @@ plugin_script_remove (struct t_weechat_plugin *weechat_plugin,
 
     plugin_script_remove_configs (weechat_plugin, script);
 
+    plugin_script_remove_themes (weechat_plugin, script);
+
     /*
      * remove again all hooks created by this script (just in case new hooks
      * were created by the calls above)

src/plugins/plugin.c

@@ -50,6 +50,7 @@
 #include "../core/core-log.h"
 #include "../core/core-network.h"
 #include "../core/core-string.h"
+#include "../core/core-theme.h"
 #include "../core/core-upgrade-file.h"
 #include "../core/core-utf8.h"
 #include "../core/core-util.h"
@@ -799,6 +800,9 @@ plugin_load (const char *filename, int init_plugin, int argc, char **argv)
         new_plugin->config_set_desc_plugin = &plugin_api_config_set_desc_plugin;
         new_plugin->config_unset_plugin = &plugin_api_config_unset_plugin;
 
+        new_plugin->theme_register = &theme_register;
+        new_plugin->theme_unregister_script = &theme_unregister_script;
+
         new_plugin->key_bind = &gui_key_bind_plugin;
         new_plugin->key_unbind = &gui_key_unbind_plugin;
 
@@ -1214,6 +1218,9 @@ plugin_remove (struct t_weechat_plugin *plugin)
     /* remove all configuration files */
     config_file_free_all_plugin (plugin);
 
+    /* remove all theme contributions registered by this plugin */
+    theme_unregister_plugin (plugin);
+
     /* remove all hooks */
     unhook_all_plugin (plugin, NULL);
 

src/plugins/python/weechat-python-api.c

@@ -2001,6 +2001,34 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(rc);
 }
 
+API_FUNC(theme_register)
+{
+    char *name;
+    PyObject *dict;
+    struct t_hashtable *hashtable;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    name = NULL;
+    dict = NULL;
+    if (!PyArg_ParseTuple (args, "sO", &name, &dict))
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    hashtable = weechat_python_dict_to_hashtable (dict,
+                                                  WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                                  WEECHAT_HASHTABLE_STRING,
+                                                  WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_python_plugin,
+                             python_current_script,
+                             name, hashtable));
+
+    weechat_hashtable_free (hashtable);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     char *context;
@@ -5729,6 +5757,7 @@ PyMethodDef weechat_python_funcs[] =
     API_DEF_FUNC(config_set_plugin),
     API_DEF_FUNC(config_set_desc_plugin),
     API_DEF_FUNC(config_unset_plugin),
+    API_DEF_FUNC(theme_register),
     API_DEF_FUNC(key_bind),
     API_DEF_FUNC(key_unbind),
     API_DEF_FUNC(prefix),

src/plugins/python/weechat.pyi

@@ -1143,6 +1143,19 @@ def config_unset_plugin(option_name: str) -> int:
     ...
 
 
+def theme_register(name: str, overrides: Dict[str, str]) -> str:
+    """`theme_register in WeeChat plugin API reference <https://weechat.org/doc/weechat/api/#_theme_register>`_
+    ::
+
+        # example
+        weechat.theme_register("light", {
+            "irc.color.input_nick": "cyan",
+            "irc.color.topic_old": "darkgray",
+        })
+    """
+    ...
+
+
 def key_bind(context: str, keys: Dict[str, str]) -> int:
     """`key_bind in WeeChat plugin API reference <https://weechat.org/doc/weechat/api/#_key_bind>`_
     ::

src/plugins/relay/CMakeLists.txt

@@ -34,6 +34,7 @@ set(RELAY_SRC
   relay-raw.c relay-raw.h
   relay-remote.c relay-remote.h
   relay-server.c relay-server.h
+  relay-theme.c relay-theme.h
   relay-upgrade.c relay-upgrade.h
   relay-websocket.c relay-websocket.h
   # irc relay

src/plugins/relay/api/relay-api-msg.c

@@ -350,9 +350,13 @@ relay_api_msg_buffer_to_json (struct t_gui_buffer *buffer,
 {
     struct t_hdata *hdata;
     struct t_gui_buffer *pointer;
+    struct t_gui_lines *ptr_lines;
+    struct t_gui_line *ptr_line;
+    struct t_gui_line_data *ptr_line_data;
     cJSON *json, *json_local_vars, *json_lines, *json_nicklist_root;
     const char *ptr_string;
     char *string;
+    int last_read_line_id;
 
     hdata = relay_hdata_buffer;
     pointer = buffer;
@@ -405,6 +409,24 @@ relay_api_msg_buffer_to_json (struct t_gui_buffer *buffer,
         if (json_lines)
             cJSON_AddItemToObject (json, "lines", json_lines);
     }
+    last_read_line_id = -1;
+    ptr_lines = weechat_hdata_pointer (relay_hdata_buffer, buffer, "own_lines");
+    if (ptr_lines)
+    {
+        ptr_line = weechat_hdata_pointer (relay_hdata_lines, ptr_lines, "last_read_line");
+        if (ptr_line)
+        {
+            ptr_line_data = weechat_hdata_pointer (relay_hdata_line, ptr_line, "data");
+            if (ptr_line_data)
+            {
+                last_read_line_id = weechat_hdata_integer (relay_hdata_line_data,
+                                                           ptr_line_data, "id");
+            }
+        }
+    }
+    cJSON_AddItemToObject (
+        json, "last_read_line_id",
+        cJSON_CreateNumber (last_read_line_id));
 
     /* nicks */
     if (nicks)

src/plugins/relay/api/relay-api.h

@@ -26,8 +26,8 @@ struct t_relay_client;
 enum t_relay_status;
 
 #define RELAY_API_VERSION_MAJOR 0
-#define RELAY_API_VERSION_MINOR 4
-#define RELAY_API_VERSION_PATCH 1
+#define RELAY_API_VERSION_MINOR 5
+#define RELAY_API_VERSION_PATCH 0
 #define RELAY_API_VERSION_NUMBER                                        \
     ((RELAY_API_VERSION_MAJOR << 16)                                    \
      + (RELAY_API_VERSION_MINOR << 8)                                   \

src/plugins/relay/api/weechat-relay-api.yaml

@@ -17,7 +17,7 @@ info:
   license:
     name: CC BY-NC-SA 4.0
     url: https://creativecommons.org/licenses/by-nc-sa/4.0/
-  version: 0.4.1
+  version: 0.5.0
 
 externalDocs:
   url: https://weechat.org/doc/
@@ -1043,6 +1043,11 @@ components:
           type: array
           items:
             $ref: '#/components/schemas/Line'
+        last_read_line_id:
+          type: integer
+          format: int64
+          description: identifier of the last line read in the buffer (-1 if read marker is not displayed)
+          example: -1
         nicklist_root:
           $ref: '#/components/schemas/NickGroup'
       required:

src/plugins/relay/relay-config.c

@@ -1909,7 +1909,7 @@ relay_config_init (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         relay_config_api_remote_input_cmd_local = weechat_config_new_option (
             relay_config_file, relay_config_section_api,
-            "remote_input_cmd_local", "string",
+            "remote_input_cmd_local", "string|themable",
             N_("text displayed after user input when the command would be "
                "executed locally (NOT sent to the remote WeeChat) "
                "(note: content is evaluated, see /help eval)"),
@@ -1917,7 +1917,7 @@ relay_config_init (void)
             NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
         relay_config_api_remote_input_cmd_remote = weechat_config_new_option (
             relay_config_file, relay_config_section_api,
-            "remote_input_cmd_remote", "string",
+            "remote_input_cmd_remote", "string|themable",
             N_("text displayed after user input when the command would be "
                "executed on the remote WeeChat (NOT executed locally) "
                "(note: content is evaluated, see /help eval)"),

src/plugins/relay/relay-http.c

@@ -1006,6 +1006,14 @@ relay_http_recv (struct t_relay_client *client, const char *data, int size)
 
     if (client->partial_message)
     {
+        /*
+         * limit the size of the partial message: once the maximum is reached,
+         * ignore the extra data (protection against a client sending a huge
+         * amount of data without any end-of-line and dribbling it, which would
+         * consume all the memory)
+         */
+        if (strlen (client->partial_message) >= RELAY_HTTP_PARTIAL_MESSAGE_MAX_LENGTH)
+            return;
         new_partial = realloc (client->partial_message,
                                strlen (client->partial_message) +
                                strlen (data) + 1);
@@ -1708,7 +1716,7 @@ relay_http_print_log_request (struct t_relay_http_request *request)
     weechat_log_printf ("    path_items. . . . . . . : %p", request->path_items);
     if (request->path_items)
     {
-        for (i = 0; request->path_items[0]; i++)
+        for (i = 0; request->path_items[i]; i++)
         {
             weechat_log_printf ("      '%s'", request->path_items[i]);
         }

src/plugins/relay/relay-http.h

@@ -64,6 +64,15 @@ enum t_relay_client_http_status
  */
 #define RELAY_HTTP_BODY_MAX_LENGTH (8 * 1024 * 1024)
 
+/*
+ * maximum length of the partial message accumulated while reading an HTTP
+ * request: once this limit is reached, the extra data is ignored; this
+ * protects against a client sending a huge amount of data without any
+ * end-of-line (an unterminated method or header line), which would consume
+ * all the memory
+ */
+#define RELAY_HTTP_PARTIAL_MESSAGE_MAX_LENGTH (8 * 1024 * 1024)
+
 struct t_relay_http_request
 {
     enum t_relay_client_http_status status; /* HTTP status                  */

src/plugins/relay/relay-theme.c

@@ -0,0 +1,73 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* relay contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "relay.h"
+#include "relay-theme.h"
+
+
+const char *relay_theme_light[][2] =
+{
+    { "relay.color.status_auth_failed",     "magenta" },
+    { "relay.color.status_authenticating",  "202" },
+    { "relay.color.status_connecting",      "default" },
+    { "relay.color.status_disconnected",    "red" },
+    { "relay.color.text_selected",          "default" },
+    { NULL,                                 NULL },
+};
+
+void
+relay_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+relay_theme_init (void)
+{
+    relay_theme_register ("light", relay_theme_light);
+}

src/plugins/relay/relay-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_RELAY_THEME_H
+#define WEECHAT_PLUGIN_RELAY_THEME_H
+
+extern void relay_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_RELAY_THEME_H */

src/plugins/relay/relay.c

@@ -38,6 +38,7 @@
 #include "relay-raw.h"
 #include "relay-remote.h"
 #include "relay-server.h"
+#include "relay-theme.h"
 #include "relay-upgrade.h"
 
 
@@ -376,6 +377,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     relay_config_read ();
 
+    relay_theme_init ();
+
     relay_network_init ();
 
     relay_command_init ();

src/plugins/ruby/weechat-ruby-api.c

@@ -2478,6 +2478,36 @@ weechat_ruby_api_config_unset_plugin (VALUE class, VALUE option)
     API_RETURN_INT(rc);
 }
 
+static VALUE
+weechat_ruby_api_theme_register (VALUE class, VALUE name, VALUE overrides)
+{
+    char *c_name;
+    struct t_hashtable *c_overrides;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (NIL_P (name) || NIL_P (overrides))
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    Check_Type (name, T_STRING);
+    Check_Type (overrides, T_HASH);
+
+    c_name = StringValuePtr (name);
+    c_overrides = weechat_ruby_hash_to_hashtable (overrides,
+                                                  WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                                  WEECHAT_HASHTABLE_STRING,
+                                                  WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_ruby_plugin,
+                             ruby_current_script,
+                             c_name, c_overrides));
+
+    weechat_hashtable_free (c_overrides);
+
+    API_RETURN_STRING(result);
+}
+
 static VALUE
 weechat_ruby_api_key_bind (VALUE class, VALUE context, VALUE keys)
 {
@@ -7078,6 +7108,7 @@ weechat_ruby_api_init (VALUE ruby_mWeechat)
     API_DEF_FUNC(config_set_plugin, 2);
     API_DEF_FUNC(config_set_desc_plugin, 2);
     API_DEF_FUNC(config_unset_plugin, 1);
+    API_DEF_FUNC(theme_register, 2);
     API_DEF_FUNC(key_bind, 2);
     API_DEF_FUNC(key_unbind, 2);
     API_DEF_FUNC(prefix, 1);

src/plugins/script/CMakeLists.txt

@@ -29,6 +29,7 @@ add_library(script MODULE
   script-info.c script-info.h
   script-mouse.c script-mouse.h
   script-repo.c script-repo.h
+  script-theme.c script-theme.h
 )
 set_target_properties(script PROPERTIES PREFIX "")
 

src/plugins/script/script-theme.c

@@ -0,0 +1,92 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* script contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "script.h"
+#include "script-theme.h"
+
+
+const char *script_theme_light[][2] =
+{
+    { "script.color.status_autoloaded",         "default" },
+    { "script.color.status_held",               "202" },
+    { "script.color.status_installed",          "21" },
+    { "script.color.status_obsolete",           "magenta" },
+    { "script.color.status_popular",            "94" },
+    { "script.color.status_running",            "23" },
+    { "script.color.status_unknown",            "red" },
+    { "script.color.text_bg_selected",          "117" },
+    { "script.color.text_date",                 "darkgray" },
+    { "script.color.text_date_selected",        "darkgray" },
+    { "script.color.text_delimiters",           "251" },
+    { "script.color.text_description",          "default" },
+    { "script.color.text_description_selected", "default" },
+    { "script.color.text_extension",            "lightblue" },
+    { "script.color.text_extension_selected",   "lightblue" },
+    { "script.color.text_name",                 "18" },
+    { "script.color.text_name_selected",        "18" },
+    { "script.color.text_selected",             "default" },
+    { "script.color.text_tags",                 "94" },
+    { "script.color.text_tags_selected",        "94" },
+    { "script.color.text_version",              "58" },
+    { "script.color.text_version_loaded",       "default" },
+    { "script.color.text_version_loaded_selected", "default" },
+    { "script.color.text_version_selected",     "58" },
+    { NULL,                                     NULL },
+};
+
+void
+script_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+script_theme_init (void)
+{
+    script_theme_register ("light", script_theme_light);
+}

src/plugins/script/script-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_SCRIPT_THEME_H
+#define WEECHAT_PLUGIN_SCRIPT_THEME_H
+
+extern void script_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_SCRIPT_THEME_H */

src/plugins/script/script.c

@@ -37,6 +37,7 @@
 #include "script-info.h"
 #include "script-mouse.h"
 #include "script-repo.h"
+#include "script-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(SCRIPT_PLUGIN_NAME);
@@ -352,6 +353,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     script_config_read ();
 
+    script_theme_init ();
+
     weechat_mkdir_home ("${weechat_cache_dir}/" SCRIPT_PLUGIN_NAME, 0755);
 
     script_command_init ();

src/plugins/spell/CMakeLists.txt

@@ -34,6 +34,7 @@ add_library(spell MODULE
   spell-config.c spell-config.h
   spell-info.c spell-info.h
   spell-speller.c spell-speller.h
+  spell-theme.c spell-theme.h
 )
 set_target_properties(spell PROPERTIES PREFIX "")
 

src/plugins/spell/spell-theme.c

@@ -0,0 +1,69 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* spell contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "spell.h"
+#include "spell-theme.h"
+
+
+const char *spell_theme_light[][2] =
+{
+    { "spell.color.misspelled", "red" },
+    { NULL,                     NULL },
+};
+
+void
+spell_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+spell_theme_init (void)
+{
+    spell_theme_register ("light", spell_theme_light);
+}

src/plugins/spell/spell-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_SPELL_THEME_H
+#define WEECHAT_PLUGIN_SPELL_THEME_H
+
+extern void spell_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_SPELL_THEME_H */

src/plugins/spell/spell.c

@@ -43,6 +43,7 @@
 #include "spell-config.h"
 #include "spell-info.h"
 #include "spell-speller.h"
+#include "spell-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(SPELL_PLUGIN_NAME);
@@ -1196,6 +1197,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     spell_config_read ();
 
+    spell_theme_init ();
+
     spell_command_init ();
 
     spell_completion_init ();

src/plugins/tcl/weechat-tcl-api.c

@@ -2035,6 +2035,32 @@ API_FUNC(config_unset_plugin)
     API_RETURN_INT(rc);
 }
 
+API_FUNC(theme_register)
+{
+    char *name;
+    struct t_hashtable *hashtable;
+    const char *result;
+
+    API_INIT_FUNC(1, "theme_register", API_RETURN_EMPTY);
+    if (objc < 3)
+        API_WRONG_ARGS(API_RETURN_EMPTY);
+
+    name = Tcl_GetString (objv[1]);
+    hashtable = weechat_tcl_dict_to_hashtable (interp, objv[2],
+                                               WEECHAT_SCRIPT_HASHTABLE_DEFAULT_SIZE,
+                                               WEECHAT_HASHTABLE_STRING,
+                                               WEECHAT_HASHTABLE_STRING);
+
+    result = API_PTR2STR(plugin_script_api_theme_register (
+                             weechat_tcl_plugin,
+                             tcl_current_script,
+                             name, hashtable));
+
+    weechat_hashtable_free (hashtable);
+
+    API_RETURN_STRING(result);
+}
+
 API_FUNC(key_bind)
 {
     char *context;
@@ -5806,6 +5832,7 @@ void weechat_tcl_api_init (Tcl_Interp *interp)
     API_DEF_FUNC(config_set_plugin);
     API_DEF_FUNC(config_set_desc_plugin);
     API_DEF_FUNC(config_unset_plugin);
+    API_DEF_FUNC(theme_register);
     API_DEF_FUNC(key_bind);
     API_DEF_FUNC(key_unbind);
     API_DEF_FUNC(prefix);

src/plugins/trigger/CMakeLists.txt

@@ -26,6 +26,7 @@ add_library(trigger MODULE
   trigger-command.c trigger-command.h
   trigger-completion.c trigger-completion.h
   trigger-config.c trigger-config.h
+  trigger-theme.c trigger-theme.h
 )
 set_target_properties(trigger PROPERTIES PREFIX "")
 

src/plugins/trigger/trigger-theme.c

@@ -0,0 +1,74 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* trigger contribution to built-in themes. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stddef.h>
+
+#include "../weechat-plugin.h"
+#include "trigger.h"
+#include "trigger-theme.h"
+
+
+const char *trigger_theme_light[][2] =
+{
+    { "trigger.color.flag_command",     "green" },
+    { "trigger.color.flag_conditions",  "94" },
+    { "trigger.color.flag_post_action", "blue" },
+    { "trigger.color.flag_regex",       "cyan" },
+    { "trigger.color.flag_return_code", "magenta" },
+    { "trigger.color.regex",            "default" },
+    { NULL,                             NULL },
+};
+
+void
+trigger_theme_register (const char *name, const char *entries[][2])
+{
+    struct t_hashtable *overrides;
+    int i;
+
+    if (!name || !entries)
+        return;
+
+    overrides = weechat_hashtable_new (32,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       WEECHAT_HASHTABLE_STRING,
+                                       NULL, NULL);
+    if (!overrides)
+        return;
+
+    for (i = 0; entries[i][0]; i++)
+        weechat_hashtable_set (overrides, entries[i][0], entries[i][1]);
+
+    weechat_theme_register (name, overrides);
+
+    weechat_hashtable_free (overrides);
+}
+
+void
+trigger_theme_init (void)
+{
+    trigger_theme_register ("light", trigger_theme_light);
+}

src/plugins/trigger/trigger-theme.h

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sébastien Helleu <flashcode@flashtux.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * This file is part of WeeChat, the extensible chat client.
+ *
+ * WeeChat is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * WeeChat is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with WeeChat.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef WEECHAT_PLUGIN_TRIGGER_THEME_H
+#define WEECHAT_PLUGIN_TRIGGER_THEME_H
+
+extern void trigger_theme_init (void);
+
+#endif /* WEECHAT_PLUGIN_TRIGGER_THEME_H */

src/plugins/trigger/trigger.c

@@ -34,6 +34,7 @@
 #include "trigger-command.h"
 #include "trigger-completion.h"
 #include "trigger-config.h"
+#include "trigger-theme.h"
 
 
 WEECHAT_PLUGIN_NAME(TRIGGER_PLUGIN_NAME);
@@ -1385,6 +1386,8 @@ weechat_plugin_init (struct t_weechat_plugin *plugin, int argc, char *argv[])
 
     trigger_config_read ();
 
+    trigger_theme_init ();
+
     /* hook some signals */
     weechat_hook_signal ("debug_dump", &trigger_debug_dump_cb, NULL, NULL);
 

src/plugins/weechat-plugin.h

@@ -62,6 +62,7 @@ struct t_hashtable;
 struct t_hdata;
 struct t_infolist;
 struct t_infolist_item;
+struct t_theme;
 struct t_upgrade_file;
 struct t_weelist;
 struct t_weelist_item;
@@ -76,7 +77,7 @@ struct t_weelist_item;
  * please change the date with current one; for a second change at same
  * date, increment the 01, otherwise please keep 01.
  */
-#define WEECHAT_PLUGIN_API_VERSION "20260530-01"
+#define WEECHAT_PLUGIN_API_VERSION "20260531-02"
 
 /* macros for defining plugin infos */
 #define WEECHAT_PLUGIN_NAME(__name)                                     \
@@ -728,6 +729,14 @@ struct t_weechat_plugin
     int (*config_unset_plugin) (struct t_weechat_plugin *plugin,
                                 const char *option_name);
 
+    /* themes */
+    struct t_theme *(*theme_register) (struct t_weechat_plugin *plugin,
+                                       const void *script,
+                                       const char *name,
+                                       struct t_hashtable *overrides);
+    void (*theme_unregister_script) (struct t_weechat_plugin *plugin,
+                                     const void *script);
+
     /* key bindings */
     int (*key_bind) (const char *context, struct t_hashtable *keys);
     int (*key_unbind) (const char *context, const char *key);
@@ -1855,6 +1864,13 @@ extern int weechat_plugin_end (struct t_weechat_plugin *plugin);
 #define weechat_config_unset_plugin(__option)                           \
     (weechat_plugin->config_unset_plugin)(weechat_plugin, __option)
 
+/* themes */
+#define weechat_theme_register(__name, __overrides)                     \
+    (weechat_plugin->theme_register)(weechat_plugin, NULL,              \
+                                     __name, __overrides)
+#define weechat_theme_unregister_script(__script)                       \
+    (weechat_plugin->theme_unregister_script)(weechat_plugin, __script)
+
 /* key bindings */
 #define weechat_key_bind(__context, __keys)                             \
     (weechat_plugin->key_bind)(__context, __keys)

src/plugins/xfer/CMakeLists.txt

@@ -30,6 +30,7 @@ add_library(xfer MODULE
   xfer-file.c xfer-file.h
   xfer-info.c xfer-info.h
   xfer-network.c xfer-network.h
+  xfer-theme.c xfer-theme.h
   xfer-upgrade.c xfer-upgrade.h
 )
 set_target_properties(xfer PROPERTIES PREFIX "")

src/plugins/xfer/xfer-chat.c

@@ -162,7 +162,7 @@ xfer_chat_recv_cb (const void *pointer, void *data, int fd)
             {
                 ctcp_action = 0;
                 length = strlen (ptr_buf);
-                if (ptr_buf[length - 1] == '\r')
+                if ((length > 0) && (ptr_buf[length - 1] == '\r'))
                 {
                     ptr_buf[length - 1] = '\0';
                     length--;