theme: support theme setting override

...by reading <config-dir>/themerc-override where <config-dir> is normally
$HOME/.config/labwc can be other locations as described in labwc-config(5)
and can also be specified by the command line option -C.

The reason for supporting theme override is to give users more fine-
grained control of settings without making local copies and modifying
themes.

README.md

@@ -169,11 +169,12 @@ User config files are located at `${XDG_CONFIG_HOME:-$HOME/.config/labwc/}`
 with the following four files being used:
 
 | file               | man page
-| ------------- | --------
+| ------------------ | --------
 | [rc.xml]           | [labwc-config(5)], [labwc-actions(5)]
 | [menu.xml]         | [labwc-menu(5)]
 | [autostart]        | [labwc(1)]
 | [environment]      | [labwc-config(5)]
+| [themerc-override] | [labwc-theme(5)]
 
 The example [rc.xml] has been kept simple. For all options and default values,
 see [rc.xml.all]
@@ -259,6 +260,7 @@ See [integration] for further details.
 [autostart]: docs/autostart
 [environment]: docs/environment
 [themerc]: docs/themerc
+[themerc-override]: docs/themerc
 
 [labwc(1)]: https://labwc.github.io/labwc.1.html
 [labwc-config(5)]: https://labwc.github.io/labwc-config.5.html

docs/README

@@ -3,5 +3,7 @@ Config layout for ~/.config/labwc/
 - environment
 - menu.xml
 - rc.xml
+- themerc-override
+
+See `man labwc-config and `man labwc-theme` for further details.
 
-See man labwc-config for further details.

docs/labwc-config.5.scd

@@ -18,6 +18,9 @@ searched for in the following order:
 - ${XDG_CONFIG_HOME:-$HOME/.config}/labwc
 - ${XDG_CONFIG_DIRS:-/etc/xdg}/labwc
 
+The configuration directory location can be override with the -C command line
+option.
+
 All configuration and theme files except autostart are re-loaded on receiving
 signal SIGHUP.
 

docs/labwc-theme.5.scd

@@ -20,6 +20,11 @@ the rc.xml configuration file (labwc-config(5)).
 
 A theme consists of a themerc file and optionally some xbm icons.
 
+Theme settings specified in themerc can be overridden by creating a
+'themerc-override' file in the configuration directory, which is normally
+$HOME/.config/labwc/ but can be a few other locations as described in
+labwc-config(5).
+
 # DATA TYPES
 
 *color RGB values*

docs/meson.build

@@ -30,6 +30,7 @@ install_data(
     'environment',
     'menu.xml',
     'README',
+    'themerc',
     'rc.xml',
     'rc.xml.all'
   ],

docs/themerc

@@ -1,3 +1,10 @@
+# This file contains all themerc options with default values
+#
+# System-wide and local themes can be overridden by creating a copy of this
+# file and renaming it to $HOME/.config/labwc/themerc-override. Be careful
+# though - if you only want to override a small number of specific options,
+# make sure all other lines are commented out or deleted.
+
 # general
 border.width: 1
 padding.height: 3

src/theme.c

@@ -372,6 +372,32 @@ theme_read(struct theme *theme, const char *theme_name)
 	fclose(stream);
 }
 
+static void
+theme_read_override(struct theme *theme)
+{
+	char f[4096] = { 0 };
+	snprintf(f, sizeof(f), "%s/themerc-override", rc.config_dir);
+
+	FILE *stream = fopen(f, "r");
+	if (!stream) {
+		wlr_log(WLR_INFO, "no theme override '%s'", f);
+		return;
+	}
+
+	wlr_log(WLR_INFO, "read theme-override %s", f);
+	char *line = NULL;
+	size_t len = 0;
+	while (getline(&line, &len, stream) != -1) {
+		char *p = strrchr(line, '\n');
+		if (p) {
+			*p = '\0';
+		}
+		process_line(theme, line);
+	}
+	free(line);
+	fclose(stream);
+}
+
 struct rounded_corner_ctx {
 	struct wlr_box *box;
 	double radius;
@@ -552,7 +578,12 @@ theme_init(struct theme *theme, const char *theme_name)
 	 */
 	theme_builtin(theme);
 
+	/* Read <data-dir>/share/themes/$theme_name/openbox-3/themerc */
 	theme_read(theme, theme_name);
+
+	/* Read <config-dir>/labwc/themerc-override */
+	theme_read_override(theme);
+
 	post_processing(theme);
 	create_corners(theme);
 	xbm_load(theme);