[PATCH] config: Introduce GIT_CONFIG_NOGLOBAL

[Patrick Steinhardt <ps@pks.im>]

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While it's already possible to stop git from reading the system config
via GIT_CONFIG_NOSYSTEM, doing the same for global config files requires
the user to unset both HOME and XDG_CONFIG_HOME. This is an awkward
interface and may even pose a problem e.g. when git hooks rely on these
variables to be present.

Introduce a new GIT_CONFIG_NOGLOBAL envvar, which is the simple
equivalent to GIT_CONFIG_NOSYSTEM. If set to true, git will skip reading
both `~/.gitconfig` and `$XDG_CONFIG_HOME/git/config`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-config.txt |  4 ++++
 Documentation/git.txt        | 16 ++++++++++++----
 config.c                     |  9 +++++++--
 t/t1300-config.sh            | 31 +++++++++++++++++++++++++++++++
 4 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 4b4cc5c5e8..88cd064abb 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -340,6 +340,10 @@ GIT_CONFIG::
 	Using the "--global" option forces this to ~/.gitconfig. Using the
 	"--system" option forces this to $(prefix)/etc/gitconfig.
 
+GIT_CONFIG_NOGLOBAL::
+	Whether to skip reading settings from the global ~/.gitconfig and
+	$XDG_CONFIG_HOME/git/config files. See linkgit:git[1] for details.
+
 GIT_CONFIG_NOSYSTEM::
 	Whether to skip reading settings from the system-wide
 	$(prefix)/etc/gitconfig file. See linkgit:git[1] for details.
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 3a9c44987f..4462bd2da9 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -670,13 +670,21 @@ for further details.
 	If this environment variable is set to `0`, git will not prompt
 	on the terminal (e.g., when asking for HTTP authentication).
 
+`GIT_CONFIG_NOGLOBAL`::
+	Whether to skip reading settings from the system-wide `~/.gitconfig`
+	and `$XDG_CONFIG_HOME/git/config` files.  This environment variable can
+	be used along with `$GIT_CONFIG_NOSYSTEM` to create a predictable
+	environment for a picky script, or you can set it temporarily to avoid
+	using a buggy global config file while waiting for someone with
+	sufficient permissions to fix it.
+
 `GIT_CONFIG_NOSYSTEM`::
 	Whether to skip reading settings from the system-wide
 	`$(prefix)/etc/gitconfig` file.  This environment variable can
-	be used along with `$HOME` and `$XDG_CONFIG_HOME` to create a
-	predictable environment for a picky script, or you can set it
-	temporarily to avoid using a buggy `/etc/gitconfig` file while
-	waiting for someone with sufficient permissions to fix it.
+	be used along with `$GIT_CONFIG_NOGLOBAL` to create a predictable
+	environment for a picky script, or you can set it temporarily to avoid
+	using a buggy `/etc/gitconfig` file while waiting for someone with
+	sufficient permissions to fix it.
 
 `GIT_FLUSH`::
 	If this environment variable is set to "1", then commands such
diff --git a/config.c b/config.c
index 6428393a41..19c1b31c75 100644
--- a/config.c
+++ b/config.c
@@ -1879,6 +1879,11 @@ int git_config_system(void)
 	return !git_env_bool("GIT_CONFIG_NOSYSTEM", 0);
 }
 
+static int git_config_global(void)
+{
+	return !git_env_bool("GIT_CONFIG_NOGLOBAL", 0);
+}
+
 static int do_git_config_sequence(const struct config_options *opts,
 				  config_fn_t fn, void *data)
 {
@@ -1903,10 +1908,10 @@ static int do_git_config_sequence(const struct config_options *opts,
 					    data);
 
 	current_parsing_scope = CONFIG_SCOPE_GLOBAL;
-	if (xdg_config && !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK))
+	if (git_config_global() && xdg_config && !access_or_die(xdg_config, R_OK, ACCESS_EACCES_OK))
 		ret += git_config_from_file(fn, xdg_config, data);
 
-	if (user_config && !access_or_die(user_config, R_OK, ACCESS_EACCES_OK))
+	if (git_config_global() && user_config && !access_or_die(user_config, R_OK, ACCESS_EACCES_OK))
 		ret += git_config_from_file(fn, user_config, data);
 
 	current_parsing_scope = CONFIG_SCOPE_LOCAL;
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index e0dd5d65ce..0754189974 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -2059,6 +2059,37 @@ test_expect_success '--show-scope with --show-origin' '
 	test_cmp expect output
 '
 
+test_expect_success 'GIT_CONFIG_NOGLOBAL' '
+	test_when_finished rm -f "$HOME"/.config/git &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = true
+	EOF
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = true
+	EOF
+	cat >.git/config <<-EOF &&
+	[local]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	xdg.config=true
+	global	home.config=true
+	local	local.config=true
+	EOF
+	git config --show-scope --list >output &&
+	test_cmp expect output &&
+
+	cat >expect <<-EOF &&
+	local	local.config=true
+	EOF
+	GIT_CONFIG_NOGLOBAL=true git config --show-scope --list >output &&
+	test_cmp expect output
+'
+
 for opt in --local --worktree
 do
 	test_expect_success "$opt requires a repo" '
-- 
2.31.1


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