config: add config_from_gitmodules

Add 'config_from_gitmodules()' function which can be used by 'fetch' and
'update_clone' in order to maintain backwards compatibility with
configuration being stored in .gitmodules' since a future patch will
remove reading these values in the submodule-config.

This function should not be used anywhere other than in 'fetch' and
'update_clone'.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -2053,6 +2053,23 @@ int git_config_get_pathname(const char *key, const char **dest)
 	return repo_config_get_pathname(the_repository, key, dest);
 }
 
+/*
+ * Note: This function exists solely to maintain backward compatibility with
+ * 'fetch' and 'update_clone' storing configuration in '.gitmodules' and should
+ * NOT be used anywhere else.
+ *
+ * Runs the provided config function on the '.gitmodules' file found in the
+ * working directory.
+ */
+void config_from_gitmodules(config_fn_t fn, void *data)
+{
+	if (the_repository->worktree) {
+		char *file = repo_worktree_path(the_repository, GITMODULES_FILE);
+		git_config_from_file(fn, file, data);
+		free(file);
+	}
+}
+
 int git_config_get_expiry(const char *key, const char **output)
 {
 	int ret = git_config_get_string_const(key, output);

config.h

@@ -187,6 +187,16 @@ extern int repo_config_get_maybe_bool(struct repository *repo,
 extern int repo_config_get_pathname(struct repository *repo,
 				    const char *key, const char **dest);
 
+/*
+ * Note: This function exists solely to maintain backward compatibility with
+ * 'fetch' and 'update_clone' storing configuration in '.gitmodules' and should
+ * NOT be used anywhere else.
+ *
+ * Runs the provided config function on the '.gitmodules' file found in the
+ * working directory.
+ */
+extern void config_from_gitmodules(config_fn_t fn, void *data);
+
 extern int git_config_get_value(const char *key, const char **value);
 extern const struct string_list *git_config_get_value_multi(const char *key);
 extern void git_config_clear(void);