irc: contribute "light" theme overrides

Add irc-theme.{c,h} with the IRC plugin contribution to the built-in
"light" theme: 9 overrides on irc.color.* options tuned for a
light-background terminal (input_nick, item_lag_finished,
item_tls_version_deprecated, list_buffer_line_selected,
message_chghost, message_setname, nick_prefixes, topic_new, topic_old).

The registration is a small wrapper around weechat_theme_register that
builds a hashtable from a static (option, value) table and frees it
after the call. irc_theme_init() is called from weechat_plugin_init
after irc_config_init/read so the option names are already created
when the theme registry references them.

Default option values are NOT changed.

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-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 ();