util: change the builddir_lookup() to return a boolean

All but one callers of this function only care about yes/no, so let's
change it to only return the build dir in the one case it's needed.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1175>

src/builddir.h

@@ -30,10 +30,10 @@
 
 /**
  * Try to figure out the directory we're executing from and if it matches
- * the builddir, return that directory. Otherwise, return NULL.
+ * the builddir true and set builddir (if not NULL) to the given builddir.
  */
-static inline char *
-builddir_lookup(void)
+static inline bool
+builddir_lookup(char **builddir)
 {
 	char execdir[PATH_MAX];
 	char *pathsep;
@@ -42,11 +42,11 @@ builddir_lookup(void)
 	/* In the case of release builds, the builddir is
 	   the empty string */
 	if (streq(MESON_BUILD_ROOT, ""))
-		return NULL;
+		return false;
 
 	nread = readlink("/proc/self/exe", execdir, sizeof(execdir) - 1);
 	if (nread <= 0 || nread == sizeof(execdir) - 1)
-		return NULL;
+		return false;
 
 	/* readlink doesn't terminate the string and readlink says
 	   anything past sz is undefined */
@@ -54,11 +54,14 @@ builddir_lookup(void)
 
 	pathsep = strrchr(execdir, '/');
 	if (!pathsep)
-		return NULL;
+		return false;
 
 	*pathsep = '\0';
 	if (!streq(execdir, MESON_BUILD_ROOT))
-		return NULL;
+		return false;
 
-	return safe_strdup(execdir);
+	if (builddir)
+		*builddir = safe_strdup(execdir);
+
+	return true;
 }

test/litest.c

@@ -4961,16 +4961,13 @@ litest_parse_argv(int argc, char **argv, int *njobs_out)
 		JOBS_SINGLE,
 		JOBS_CUSTOM
 	} want_jobs = JOBS_DEFAULT;
-	char *builddir;
 	char *jobs_env;
 	int jobs = 0;
 
 	/* If we are not running from the builddir, we assume we're running
 	 * against the system as installed */
-	builddir = builddir_lookup();
-	if (!builddir)
+	if (!builddir_lookup(NULL))
 		use_system_rules_quirks = true;
-	free(builddir);
 
 	if (in_debugger)
 		want_jobs = JOBS_SINGLE;

test/test-builddir-lookup.c

@@ -28,21 +28,24 @@
 int
 main(int argc, char **argv)
 {
-	char *builddir;
+	char *builddir = NULL;
 	char *mode;
 
 	assert(argc == 2);
 	mode = argv[1];
 
-	builddir = builddir_lookup();
+	bool is_builddir = builddir_lookup(&builddir);
 	if (streq(mode, "--builddir-is-null")) {
+		assert(!is_builddir);
 		assert(builddir == NULL);
 	} else if (streq(mode, "--builddir-is-set")) {
 		/* In the case of release builds, the builddir is
 		   the empty string */
 		if (streq(MESON_BUILD_ROOT, "")) {
+			assert(!is_builddir);
 			assert(builddir == NULL);
 		} else {
+			assert(is_builddir);
 			assert(builddir);
 			assert(streq(MESON_BUILD_ROOT, builddir));
 		}

tools/libinput-quirks.c

@@ -166,10 +166,8 @@ main(int argc, char **argv)
 
 	/* Overriding the data dir means no custom override file */
 	if (!data_path) {
-		char *builddir = builddir_lookup();
-		if (builddir) {
+		if (builddir_lookup(NULL)) {
 			data_path = LIBINPUT_QUIRKS_SRCDIR;
-			free(builddir);
 		} else {
 			data_path = LIBINPUT_QUIRKS_DIR;
 			override_file = LIBINPUT_QUIRKS_OVERRIDE_FILE;

tools/libinput-record.c

@@ -1799,19 +1799,16 @@ print_device_quirks(struct record_device *dev)
 	struct quirks_context *quirks;
 	const char *data_path = LIBINPUT_QUIRKS_DIR;
 	const char *override_file = LIBINPUT_QUIRKS_OVERRIDE_FILE;
-	char *builddir = NULL;
 
 	if (stat(dev->devnode, &st) < 0)
 		return;
 
-	if ((builddir = builddir_lookup())) {
+	if (builddir_lookup(NULL)) {
 		setenv("LIBINPUT_QUIRKS_DIR", LIBINPUT_QUIRKS_SRCDIR, 0);
 		data_path = LIBINPUT_QUIRKS_SRCDIR;
 		override_file = NULL;
 	}
 
-	free(builddir);
-
 	quirks = quirks_init_subsystem(data_path,
 				       override_file,
 				       quirks_log_handler,

tools/shared.c

@@ -538,10 +538,8 @@ tools_open_device(const char **paths, bool verbose, bool *grab)
 static void
 tools_setenv_quirks_dir(void)
 {
-	char *builddir = builddir_lookup();
-	if (builddir) {
+	if (builddir_lookup(NULL)) {
 		setenv("LIBINPUT_QUIRKS_DIR", LIBINPUT_QUIRKS_SRCDIR, 0);
-		free(builddir);
 	}
 }
 
@@ -765,8 +763,9 @@ setup_path(void)
 	const char *path = getenv("PATH");
 	char new_path[PATH_MAX];
 	const char *extra_path = LIBINPUT_TOOL_PATH;
-	char *builddir = builddir_lookup();
+	char *builddir = NULL;
 
+	builddir_lookup(&builddir);
 	snprintf(new_path,
 		 sizeof(new_path),
 		 "%s:%s",