config: add include_one directive

Adds include_one <pattern1> <pattern2>, which loads all files
matching pattern1, then loads files from pattern2 only if their
basename was not already loaded from pattern1.

This allows user configs in ~/.config/sway/conf.d/ to shadow
distro-provided defaults in /etc/sway/conf.d/ by filename without
completely overriding the include path — a common pain point for
packagers on NixOS, Fedora, and similar distributions.

Edge cases handled:
- pattern1 matches nothing: all pattern2 files load normally
- Same basename in both: pattern1 file wins, pattern2 skipped
- Neither pattern matches: silently succeeds (matches include behavior)

include/sway/commands.h

@@ -145,6 +145,7 @@ sway_cmd cmd_fullscreen;
 sway_cmd cmd_gaps;
 sway_cmd cmd_hide_edge_borders;
 sway_cmd cmd_include;
+sway_cmd cmd_include_one;
 sway_cmd cmd_inhibit_idle;
 sway_cmd cmd_input;
 sway_cmd cmd_seat;

include/sway/config.h

@@ -621,6 +621,14 @@ bool load_main_config(const char *path, bool is_active, bool validating);
 void load_include_configs(const char *path, struct sway_config *config,
 		struct swaynag_instance *swaynag);
 
+/**
+ * Loads included configs using basename-based shadowing.
+ * Files from pattern1 are always loaded. Files from pattern2 are loaded
+ * only if their basename was not already loaded from pattern1.
+ */
+void load_include_one_configs(const char *pattern1, const char *pattern2,
+        struct sway_config *config, struct swaynag_instance *swaynag);
+
 /**
  * Reads the config from the given FILE.
  */

sway/commands.c

@@ -103,6 +103,7 @@ static const struct cmd_handler handlers[] = {
 static const struct cmd_handler config_handlers[] = {
 	{ "default_orientation", cmd_default_orientation },
 	{ "include", cmd_include },
+	{ "include_one", cmd_include_one },
 	{ "primary_selection", cmd_primary_selection },
 	{ "swaybg_command", cmd_swaybg_command },
 	{ "swaynag_command", cmd_swaynag_command },

sway/commands/include_one.c

@@ -0,0 +1,12 @@
+#include "sway/commands.h"
+#include "sway/config.h"
+
+struct cmd_results *cmd_include_one(int argc, char **argv) {
+	struct cmd_results *error = NULL;
+	if ((error = checkarg(argc, "include_one", EXPECTED_EQUAL_TO, 2))) {
+		return error;
+	}
+	load_include_one_configs(argv[0], argv[1], config,
+			&config->swaynag_config_errors);
+	return cmd_results_new(CMD_SUCCESS, NULL);
+}

sway/config.c

@@ -623,6 +623,72 @@ cleanup:
 	free(wd);
 }
 
+void load_include_one_configs(const char *pattern1, const char *pattern2,
+		struct sway_config *config, struct swaynag_instance *swaynag) {
+	char *wd = getcwd(NULL, 0);
+	if (!wd) {
+		sway_log(SWAY_ERROR, "include_one: failed to get working directory");
+		return;
+	}
+	char *parent_path = strdup(config->current_config_path);
+	const char *parent_dir = dirname(parent_path);
+	if (chdir(parent_dir) < 0) {
+		sway_log(SWAY_ERROR, "include_one: failed to change working directory");
+		goto cleanup;
+	}
+
+	list_t *loaded_basenames = create_list();
+	if (!loaded_basenames) {
+		sway_log(SWAY_ERROR, "include_one: failed to allocate list");
+		goto cleanup;
+	}
+
+	wordexp_t p;
+	if (wordexp(pattern1, &p, 0) == 0) {
+		char **w = p.we_wordv;
+		for (size_t i = 0; i < p.we_wordc; i++) {
+			if (load_include_config(w[i], config, swaynag)) {
+				char *tmp = strdup(w[i]);
+				list_add(loaded_basenames, strdup(basename(tmp)));
+				free(tmp);
+			}
+		}
+		wordfree(&p);
+	}
+
+	if (wordexp(pattern2, &p, 0) == 0) {
+		char **w = p.we_wordv;
+		for (size_t i = 0; i < p.we_wordc; i++) {
+			char *tmp = strdup(w[i]);
+			char *base = basename(tmp);
+			bool already_loaded = false;
+			for (int j = 0; j < loaded_basenames->length; j++) {
+				if (strcmp(loaded_basenames->items[j], base) == 0) {
+					already_loaded = true;
+					break;
+				}
+			}
+			if (!already_loaded) {
+				load_include_config(w[i], config, swaynag);
+			}
+			free(tmp);
+		}
+		wordfree(&p);
+	}
+
+	for (int i = 0; i < loaded_basenames->length; i++) {
+		free(loaded_basenames->items[i]);
+	}
+	list_free(loaded_basenames);
+
+	if (chdir(wd) < 0) {
+		sway_log(SWAY_ERROR, "failed to change working directory");
+	}
+cleanup:
+	free(parent_path);
+	free(wd);
+}
+
 void run_deferred_commands(void) {
 	if (!config->cmd_queue->length) {
 		return;

sway/meson.build

@@ -76,6 +76,7 @@ sway_sources = files(
 	'commands/max_render_time.c',
 	'commands/opacity.c',
 	'commands/include.c',
+	'commands/include_one.c',
 	'commands/input.c',
 	'commands/layout.c',
 	'commands/mode.c',

sway/sway.5.scd

@@ -72,6 +72,13 @@ The following commands may only be used in the configuration file.
 	*wordexp*(3) for details). The same include file can only be included once;
 	subsequent attempts will be ignored.
 
+*include_one* <pattern1> <pattern2>
+	Include files from _pattern1_. Then include files from _pattern2_ only
+	if a file with the same basename was not already included from
+	_pattern1_. Both patterns expand shell syntax (see *wordexp*(3) for
+	details). This allows user configs to shadow distro-provided defaults
+	by filename.
+
 *swaybg_command* <command>
 	Executes custom background _command_. Default is _swaybg_. Refer to
 	*sway-output*(5) for more information.