config: read global scope via config_sequence

When both `$HOME/.gitconfig` and `$XDG_CONFIG_HOME/git/config` exist,
`git config list --global` and `git config --get --global` read the home
configuration file but ignore the XDG file. Bug reporters expected these
commands to read both files and be consistent with the documentation and
the behaviour of the unscoped `git config list` and `git config --get`
commands [1][2], which read from both files (in addition to
system-wide and repository-specific entries, of course).

We assume each scope corresponds to a single configuration file. So,
during `--global` operations, Git selects a single path and passes it to
`git_config_from_file_with_options(path)`. Since global configuration
comes from two files, we should read the configuration files with
another method.

Running `git config list --show-scope --show-origin` (without
`--global`) reads both the home and XDG files. So there's existing code
that respects both locations, namely `do_git_config_sequence()` which
reads from all scopes. Introduce flags to ignore all but the global
scope (i.e. ignore system, local, worktree, and cmdline). Then, reuse
the function to read only the global scope when `--global` is specified.
This was the suggested solution [3] in the original bug report.

Modify tests to check that both configuration files are respected during
`--global` read operations and add tests to ensure we do not introduce
regressions. Specifically:
  - The home config should take precedence over the XDG config.

  - `git config list` should not fail on non-existent global config.

  - `git config list --global` should fail when both global config files
    are non-existent. It should not fail if at least one of them exists.

Implementation notes:
  - The `ignore_global` flag is not set anywhere, so the
    `if (!opts->ignore_global)` condition is always met. Include the
    flag for completeness.

  - Keep populating `opts->source.file` in `builtin/config.c` because it
    is used as the destination config file for write operations. The
    proposed changes could convolute the code because there is no single
    source of truth for the config file locations in the global scope.
    Add a comment to clarify this.

[1] https://lore.kernel.org/git/CAFA9we-QLQRzJdGMMCPatmfrk1oHeiUu9msMRXXk1MLE5HRxBQ@mail.gmail.com/
[2] https://lore.kernel.org/git/CAAdFe9yhBk-WecVzCTsjQ-4Z3AZAbpP+w+B076ouM3qX6d1WAg@mail.gmail.com/
[3] https://lore.kernel.org/git/kl6ly1oze7wb.fsf@chooglen-macbookpro.roam.corp.google.com

Reported-by: Jade Lovelace <lists@jade.fyi>
Reported-by: Nils Fahldieck <nils@fahldieck.de>
Suggested-by: Glen Choo <glencbz@gmail.com>
Helped-by: Derrick Stolee <stolee@gmail.com>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Delilah Ashley Wu <delilahwu@microsoft.com>

Author: delilahw

builtin/config.c

@@ -957,6 +957,17 @@ static void location_options_init(struct config_location_options *opts,
 	}
 
 	if (opts->use_global_config) {
+		/*
+		 * Since global config is sourced from more than one location,
+		 * read it using `do_git_config_sequence()` with other scopes
+		 * ignored. However, writing global config should point to a
+		 * single destination, set in `opts->source.file`.
+		 */
+		opts->options.ignore_repo = 1;
+		opts->options.ignore_cmdline = 1;
+		opts->options.ignore_worktree = 1;
+		opts->options.ignore_system = 1;
+
 		opts->source.file = opts->file_to_free = git_global_config();
 		if (!opts->source.file)
 			/*

config.c

@@ -1586,26 +1586,31 @@ static int do_git_config_sequence(const struct config_options *opts,
 		worktree_config = NULL;
 	}
 
-	if (git_config_system() && system_config &&
+	if (!opts->ignore_system && git_config_system() && system_config &&
 	    !access_or_die(system_config, R_OK,
 			   opts->system_gently ? ACCESS_EACCES_OK : 0))
 		attempt_git_config_from_file_with_options(fn, system_config, data,
 							  CONFIG_SCOPE_SYSTEM, NULL,
 							  &success_count, &ret);
 
-	git_global_config_paths(&user_config, &xdg_config);
+	if (!opts->ignore_global) {
+		git_global_config_paths(&user_config, &xdg_config);
 
-	if (xdg_config && !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK))
-		attempt_git_config_from_file_with_options(fn, xdg_config,
-							  data,
-							  CONFIG_SCOPE_GLOBAL,
-							  NULL, &success_count, &ret);
+		if (xdg_config && !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK))
+			attempt_git_config_from_file_with_options(fn, xdg_config,
+								  data,
+								  CONFIG_SCOPE_GLOBAL,
+								  NULL, &success_count, &ret);
 
-	if (user_config && !access_or_die(user_config, R_OK, ACCESS_EACCES_OK))
-		attempt_git_config_from_file_with_options(fn, user_config,
-							  data,
-							  CONFIG_SCOPE_GLOBAL,
-							  NULL, &success_count, &ret);
+		if (user_config && !access_or_die(user_config, R_OK, ACCESS_EACCES_OK))
+			attempt_git_config_from_file_with_options(fn, user_config,
+								  data,
+								  CONFIG_SCOPE_GLOBAL,
+								  NULL, &success_count, &ret);
+
+		free(xdg_config);
+		free(user_config);
+	}
 
 	if (!opts->ignore_repo && repo_config &&
 	    !access_or_die(repo_config, R_OK, 0))
@@ -1623,8 +1628,6 @@ static int do_git_config_sequence(const struct config_options *opts,
 		die(_("unable to parse command-line config"));
 
 	free(system_config);
-	free(xdg_config);
-	free(user_config);
 	free(repo_config);
 	free(worktree_config);
 
@@ -1658,7 +1661,8 @@ int config_with_options(config_fn_t fn, void *data,
 	 */
 	if (config_source && config_source->use_stdin) {
 		ret = git_config_from_stdin(fn, data, config_source->scope);
-	} else if (config_source && config_source->file) {
+	} else if (config_source && config_source->file &&
+		   config_source->scope != CONFIG_SCOPE_GLOBAL) {
 		ret = git_config_from_file_with_options(fn, config_source->file,
 							data, config_source->scope,
 							NULL);

config.h

@@ -87,6 +87,8 @@ typedef int (*config_parser_event_fn_t)(enum config_event_t type,
 
 struct config_options {
 	unsigned int respect_includes : 1;
+	unsigned int ignore_system : 1;
+	unsigned int ignore_global : 1;
 	unsigned int ignore_repo : 1;
 	unsigned int ignore_worktree : 1;
 	unsigned int ignore_cmdline : 1;

t/t1300-config.sh

@@ -2437,6 +2437,77 @@ test_expect_success 'list --global with nonexistent global config fails' '
 	test_must_fail git config ${mode_prefix}list --global --show-scope
 '
 
+test_expect_success 'list and get --global with only home' '
+	rm -f "$HOME"/.config/git/config &&
+
+	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	home.config=true
+	EOF
+	git config ${mode_prefix}list --global --show-scope >actual &&
+	test_cmp expect actual &&
+
+	echo true >expect &&
+	git config ${mode_get} --global home.config >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'list and get --global with only xdg' '
+	rm -f "$HOME"/.gitconfig &&
+
+	test_when_finished rm -rf \"\$HOME\"/.config/git &&
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	xdg.config=true
+	EOF
+	git config ${mode_prefix}list --global --show-scope >actual &&
+	test_cmp expect actual &&
+
+	echo true >expect &&
+	git config ${mode_get} --global xdg.config >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'list and get --global with both home and xdg' '
+	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = home
+	EOF
+
+	test_when_finished rm -rf \"\$HOME\"/.config/git &&
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = xdg
+	EOF
+
+	cat >expect <<-EOF &&
+	global	file:$HOME/.config/git/config	xdg.config=xdg
+	global	file:$HOME/.gitconfig	home.config=home
+	EOF
+	git config ${mode_prefix}list --global --show-scope --show-origin >actual &&
+	test_cmp expect actual &&
+
+	echo xdg >expect &&
+	git config ${mode_get} --global xdg.config >actual &&
+	test_cmp expect actual &&
+
+	echo home >expect &&
+	git config ${mode_get} --global home.config >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'override global and system config' '
 	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
 	cat >"$HOME"/.gitconfig <<-EOF &&

t/t1306-xdg-files.sh

@@ -52,6 +52,8 @@ test_expect_success 'read with --get: xdg file exists and ~/.gitconfig exists' '
 	echo "	name = read_gitconfig" >>.gitconfig &&
 	echo read_gitconfig >expected &&
 	git config --get user.name >actual &&
+	test_cmp expected actual &&
+	git config --global --get user.name >actual &&
 	test_cmp expected actual
 '
 
@@ -68,7 +70,8 @@ test_expect_success 'read with --list: xdg file exists and ~/.gitconfig exists'
 	>.gitconfig &&
 	echo "[user]" >.gitconfig &&
 	echo "	name = read_gitconfig" >>.gitconfig &&
-	echo user.name=read_gitconfig >expected &&
+	echo user.name=read_config >expected &&
+	echo user.name=read_gitconfig >>expected &&
 	git config --global --list >actual &&
 	test_cmp expected actual
 '