buflist: contribute "light" theme overrides

Add buflist-theme.{c,h} with the buflist plugin contribution to the
built-in "light" theme: 5 overrides on buflist.format.* options
(buffer_current, hotlist_low, hotlist_message, lag, number) tuned for
a light-background terminal. Each target is a "string|themable" option
holding an evaluated format expression with embedded ${color:...}
references.

Follows the same pattern as the irc and fset contributions: a
NULL-terminated 2D string table consumed by a tiny local register
helper that builds a hashtable and calls weechat_theme_register;
buflist_theme_init() is called once from weechat_plugin_init after
buflist_config_init / buflist_config_read.

Default option values are NOT changed.

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-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;