config: correct file reading order in read_early_config()

Config file reading order is important because each file can override
values in the previous files and this is expected behavior. Normally
we read in this order, all in do_git_config_sequence():

1. $HOME/.gitconfig
2. $GIT_DIR/config
3. config from command line

However in read_early_config() the order may be swapped a bit if
setup_git_directory() has not been called:

1. $HOME/.gitconfig
2. $GIT_DIR/config is NOT read because .git dir is not found _yet_
3. config from command line
4. $GIT_DIR/config is now READ (after discover_git_directory() call)

The reading at step 4 could override config at step 3, which is not
the expectation.

Now that we could pass the .git dir around, we could feed
discover_git_directory() back to step 2, so that it works again, and
remove step 4.

Noticed-by: Jeff King <peff@peff.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -1504,12 +1504,20 @@ int git_config_system(void)
 	return !git_env_bool("GIT_CONFIG_NOSYSTEM", 0);
 }
 
-static int do_git_config_sequence(config_fn_t fn, void *data)
+static int do_git_config_sequence(const struct config_options *opts,
+				  config_fn_t fn, void *data)
 {
 	int ret = 0;
 	char *xdg_config = xdg_config_home("config");
 	char *user_config = expand_user_path("~/.gitconfig");
-	char *repo_config = have_git_dir() ? git_pathdup("config") : NULL;
+	char *repo_config;
+
+	if (opts->git_dir)
+		repo_config = mkpathdup("%s/config", opts->git_dir);
+	else if (have_git_dir())
+		repo_config = git_pathdup("config");
+	else
+		repo_config = NULL;
 
 	current_parsing_scope = CONFIG_SCOPE_SYSTEM;
 	if (git_config_system() && !access_or_die(git_etc_gitconfig(), R_OK, 0))
@@ -1563,7 +1571,7 @@ int git_config_with_options(config_fn_t fn, void *data,
 	else if (config_source && config_source->blob)
 		return git_config_from_blob_ref(fn, config_source->blob, data);
 
-	return do_git_config_sequence(fn, data);
+	return do_git_config_sequence(opts, fn, data);
 }
 
 static void git_config_raw(config_fn_t fn, void *data)
@@ -1613,7 +1621,6 @@ void read_early_config(config_fn_t cb, void *data)
 {
 	struct config_options opts = {0};
 	struct strbuf buf = STRBUF_INIT;
-	char *to_free = NULL;
 
 	opts.respect_includes = 1;
 
@@ -1628,20 +1635,11 @@ void read_early_config(config_fn_t cb, void *data)
 	 * call).
 	 */
 	else if (discover_git_directory(&buf))
-		opts.git_dir = to_free = xstrdup(buf.buf);
+		opts.git_dir = buf.buf;
 
 	git_config_with_options(cb, data, NULL, &opts);
 
-	if (!have_git_dir() && opts.git_dir) {
-		struct git_config_source repo_config;
-
-		memset(&repo_config, 0, sizeof(repo_config));
-		strbuf_addstr(&buf, "/config");
-		repo_config.file = buf.buf;
-		git_config_with_options(cb, data, &repo_config, &opts);
-	}
 	strbuf_release(&buf);
-	free(to_free);
 }
 
 static void git_config_check_init(void);

t/t1309-early-config.sh

@@ -47,6 +47,24 @@ test_expect_success 'ceiling #2' '
 	test xdg = "$(cat output)"
 '
 
+cmdline_config="'test.source=cmdline'"
+test_expect_success 'read config file in right order' '
+	echo "[test]source = home" >>.gitconfig &&
+	git init foo &&
+	(
+		cd foo &&
+		echo "[test]source = repo" >>.git/config &&
+		GIT_CONFIG_PARAMETERS=$cmdline_config test-config \
+			read_early_config test.source >actual &&
+		cat >expected <<-\EOF &&
+		home
+		repo
+		cmdline
+		EOF
+		test_cmp expected actual
+	)
+'
+
 test_with_config () {
 	rm -rf throwaway &&
 	git init throwaway &&