config: keep bailing on unreadable global files

The expected behaviour for `git config list` is:
  A. Without `--global`, it should not bail on unreadable/non-existent
     global config files.

  B. With `--global`, it should bail when both `$HOME/.gitconfig` and
     `$XDG_CONFIG_HOME/git/config` are unreadable. It should not bail
     when one or more of them is readable.

The previous patch introduced a regression in scenario B. Running
`git config list --global` would not fail when both global config files
are unreadable. For example,
`GIT_CONFIG_GLOBAL=does-not-exist git config list --global` exits with
status code 0.

Assuming that `config_source->scope == CONFIG_SCOPE_GLOBAL` iff the
`--global` argument is specified, use this to determine whether to bail.
When reading only the global scope and both config files are unreadable,
then adjust the return code to be non-zero.

Note: When bailing, the exit code is not determined by sum of the return
codes of the underlying operations. Instead, the exit code is modified
via a single decrement. If this is undesirable, we can change it to sum
the return codes of the underlying operations instead.

Lastly, modify the tests to remove the known breakage/regression. The
tests for scenario B will now pass.

Helped-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Delilah Ashley Wu <delilahwu@microsoft.com>

Author: delilahw

config.c

@@ -1500,8 +1500,8 @@ int git_config_system(void)
 }
 
 static int do_git_config_sequence(const struct config_options *opts,
-				  const struct repository *repo,
-				  config_fn_t fn, void *data)
+				  const struct repository *repo, config_fn_t fn,
+				  void *data, enum config_scope scope)
 {
 	int ret = 0;
 	char *system_config = git_system_config();
@@ -1534,15 +1534,34 @@ static int do_git_config_sequence(const struct config_options *opts,
 							 NULL);
 
 	if (!opts->ignore_global) {
+		int global_config_success_count = 0;
+		int nonzero_ret_on_global_config_error = scope == CONFIG_SCOPE_GLOBAL;
+
 		git_global_config_paths(&user_config, &xdg_config);
 
-		if (xdg_config && !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK))
-			ret += git_config_from_file_with_options(fn, xdg_config, data,
-						CONFIG_SCOPE_GLOBAL, NULL);
+		if (xdg_config &&
+		    !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK)) {
+			ret += git_config_from_file_with_options(fn, xdg_config,
+								 data,
+								 CONFIG_SCOPE_GLOBAL,
+								 NULL);
+			if (!ret)
+				global_config_success_count++;
+		}
+
+		if (user_config &&
+		    !access_or_die(user_config, R_OK, ACCESS_EACCES_OK)) {
+			ret += git_config_from_file_with_options(fn, user_config,
+								 data,
+								 CONFIG_SCOPE_GLOBAL,
+								 NULL);
+			if (!ret)
+				global_config_success_count++;
+		}
 
-		if (user_config && !access_or_die(user_config, R_OK, ACCESS_EACCES_OK))
-			ret += git_config_from_file_with_options(fn, user_config, data,
-						CONFIG_SCOPE_GLOBAL, NULL);
+		if (nonzero_ret_on_global_config_error &&
+		    !global_config_success_count)
+			--ret;
 
 		free(xdg_config);
 		free(user_config);
@@ -1603,7 +1622,10 @@ int config_with_options(config_fn_t fn, void *data,
 		ret = git_config_from_blob_ref(fn, repo, config_source->blob,
 					       data, config_source->scope);
 	} else {
-		ret = do_git_config_sequence(opts, repo, fn, data);
+		ret = do_git_config_sequence(opts, repo, fn, data,
+					     config_source ?
+						     config_source->scope :
+						     CONFIG_SCOPE_UNKNOWN);
 	}
 
 	if (inc.remote_urls) {

t/t1300-config.sh

@@ -2372,7 +2372,7 @@ test_expect_success 'list with nonexistent global config' '
 	git config ${mode_prefix}list --show-scope
 '
 
-test_expect_failure 'list --global with nonexistent global config' '
+test_expect_success 'list --global with nonexistent global config' '
 	rm -rf "$HOME"/.gitconfig "$HOME"/.config/git/config &&
 	test_must_fail git config ${mode_prefix}list --global --show-scope
 '
@@ -2483,7 +2483,7 @@ test_expect_success 'override global and system config' '
 	test_cmp expect output
 '
 
-test_expect_failure 'override global and system config with missing file' '
+test_expect_success 'override global and system config with missing file' '
 	test_must_fail env GIT_CONFIG_GLOBAL=does-not-exist GIT_CONFIG_SYSTEM=/dev/null git config ${mode_prefix}list --global &&
 	test_must_fail env GIT_CONFIG_GLOBAL=/dev/null GIT_CONFIG_SYSTEM=does-not-exist git config ${mode_prefix}list --system &&
 	GIT_CONFIG_GLOBAL=does-not-exist GIT_CONFIG_SYSTEM=does-not-exist git version