config: factor out global config file retrieval

Factor out code that retrieves the global config file so that we can use
it in `gc.c` as well.

Use the old name from the previous commit since this function acts
functionally the same as `git_system_config` but for “global”.

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/config.c

@@ -708,30 +708,11 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 	}
 
 	if (use_global_config) {
-		char *user_config, *xdg_config;
-
-		git_global_config_paths(&user_config, &xdg_config);
-		if (!user_config)
-			/*
-			 * It is unknown if HOME/.gitconfig exists, so
-			 * we do not know if we should write to XDG
-			 * location; error out even if XDG_CONFIG_HOME
-			 * is set and points at a sane location.
-			 */
+		given_config_source.file = git_global_config();
+		if (!given_config_source.file)
 			die(_("$HOME not set"));
-
 		given_config_source.scope = CONFIG_SCOPE_GLOBAL;
-
-		if (access_or_warn(user_config, R_OK, 0) &&
-		    xdg_config && !access_or_warn(xdg_config, R_OK, 0)) {
-			given_config_source.file = xdg_config;
-			free(user_config);
-		} else {
-			given_config_source.file = user_config;
-			free(xdg_config);
-		}
-	}
-	else if (use_system_config) {
+	} else if (use_system_config) {
 		given_config_source.file = git_system_config();
 		given_config_source.scope = CONFIG_SCOPE_SYSTEM;
 	} else if (use_local_config) {

config.c

@@ -1987,6 +1987,26 @@ char *git_system_config(void)
 	return system_config;
 }
 
+char *git_global_config(void)
+{
+	char *user_config, *xdg_config;
+
+	git_global_config_paths(&user_config, &xdg_config);
+	if (!user_config) {
+		free(xdg_config);
+		return NULL;
+	}
+
+	if (access_or_warn(user_config, R_OK, 0) && xdg_config &&
+	    !access_or_warn(xdg_config, R_OK, 0)) {
+		free(user_config);
+		return xdg_config;
+	} else {
+		free(xdg_config);
+		return user_config;
+	}
+}
+
 void git_global_config_paths(char **user_out, char **xdg_out)
 {
 	char *user_config = xstrdup_or_null(getenv("GIT_CONFIG_GLOBAL"));

config.h

@@ -382,6 +382,7 @@ int config_error_nonbool(const char *);
 #endif
 
 char *git_system_config(void);
+char *git_global_config(void);
 void git_global_config_paths(char **user, char **xdg);
 
 int git_config_parse_parameter(const char *, config_fn_t fn, void *data);