Subject: [PATCH 4/4] hook: allow runtime enabling extensions.hookStdoutToStderr

From: Adrian Ratiu <[email-masked]>
Date: Wed, 4 Feb 2026 19:33:28 +0200

Add a new config `hook.forceStdoutToStderr` which allows enabling
extensions.hookStdoutToStderr by default at runtime, both for new
and existing repositories.

This makes it easier for users to enable hook parallelization for
hooks like pre-push by enforcing output consistency. See previous
commit for a more in-depth explanation & alternatives considered.

Signed-off-by: Adrian Ratiu <[email-masked]>
---
 Documentation/config/extensions.adoc |  3 ++
 Documentation/config/hook.adoc       |  6 +++
 hook.c                               | 10 ++++
 setup.c                              | 10 ++++
 t/t1800-hook.sh                      | 74 ++++++++++++++++++++++++++++
 5 files changed, 103 insertions(+)

diff --git a/Documentation/config/extensions.adoc b/Documentation/config/extensions.adoc
index de47d97f6d..0db485dd54 100644
--- a/Documentation/config/extensions.adoc
+++ b/Documentation/config/extensions.adoc
@@ -84,6 +84,9 @@ in parallel to be grouped (de-interleaved) correctly.
 +
 Defaults to disabled. When disabled, `hook.jobs` has no effect for pre-push
 hooks, which will always be run sequentially.
++
+The extension can also be enabled by setting `hook.forceStdoutToStderr`
+to `true` in the global configuration.
 
 worktreeConfig:::
 	If enabled, then worktrees will load config settings from the
diff --git a/Documentation/config/hook.adoc b/Documentation/config/hook.adoc
index 56e6b4e5c3..a6a79a1670 100644
--- a/Documentation/config/hook.adoc
+++ b/Documentation/config/hook.adoc
@@ -23,3 +23,9 @@ hook.jobs::
 +
 This has no effect for hooks requiring separate output streams (like `pre-push`)
 unless `extensions.hookStdoutToStderr` is enabled.
+
+hook.forceStdoutToStderr::
+	A boolean that enables the `extensions.hookStdoutToStderr` behavior
+	(merging stdout to stderr for all hooks) globally. This effectively
+	forces all hooks to behave as if the extension was enabled, allowing
+	parallel execution for hooks like `pre-push`.
diff --git a/hook.c b/hook.c
index e07e8f4efe..bae6e35943 100644
--- a/hook.c
+++ b/hook.c
@@ -264,6 +264,16 @@ static unsigned int get_hook_jobs(struct repository *r, struct run_hooks_opt *op
 {
 	unsigned int jobs = options->jobs;
 
+	/*
+	 * Allow hook.forceStdoutToStderr to enable extensions.hookStdoutToStderr
+	 * for existing repositories (runtime override).
+	 */
+	if (!options->stdout_to_stderr) {
+		int v = 0;
+		repo_config_get_bool(r, "hook.forceStdoutToStderr", &v);
+		options->stdout_to_stderr = v;
+	}
+
 	/*
 	 * Hooks which configure stdout_to_stderr=0 (like pre-push), expect separate
 	 * output streams. Unless extensions.StdoutToStderr is enabled (which forces
diff --git a/setup.c b/setup.c
index cf4949c086..037ab2e21d 100644
--- a/setup.c
+++ b/setup.c
@@ -2310,6 +2310,7 @@ void initialize_repository_version(int hash_algo,
 {
 	struct strbuf repo_version = STRBUF_INIT;
 	int target_version = GIT_REPO_VERSION;
+	int default_hook_stdout_to_stderr = 0;
 
 	/*
 	 * Note that we initialize the repository version to 1 when the ref
@@ -2348,6 +2349,15 @@ void initialize_repository_version(int hash_algo,
 		clear_repository_format(&repo_fmt);
 	}
 
+	repo_config_get_bool(the_repository, "hook.forceStdoutToStderr",
+			     &default_hook_stdout_to_stderr);
+	if (default_hook_stdout_to_stderr) {
+		/* extensions.hookstdouttostderr requires at least version 1 */
+		if (target_version == 0)
+			target_version = 1;
+		repo_config_set(the_repository, "extensions.hookstdouttostderr", "true");
+	}
+
 	strbuf_addf(&repo_version, "%d", target_version);
 	repo_config_set(the_repository, "core.repositoryformatversion", repo_version.buf);
 
diff --git a/t/t1800-hook.sh b/t/t1800-hook.sh
index bf19579f3a..db0f96f778 100755
--- a/t/t1800-hook.sh
+++ b/t/t1800-hook.sh
@@ -649,4 +649,78 @@ test_expect_success 'hook.jobs=2 config runs hooks in parallel' '
 	test $duration -lt 4
 '
 
+test_expect_success '`git init` respects hook.forceStdoutToStderr' '
+	test_when_finished "rm -rf repo-init" &&
+	test_config_global hook.forceStdoutToStderr true &&
+	git init repo-init &&
+	git -C repo-init config extensions.hookStdoutToStderr >actual &&
+	echo true >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '`git init` does not set extensions.hookStdoutToStderr by default' '
+	test_when_finished "rm -rf upstream" &&
+	git init upstream &&
+	test_must_fail git -C upstream config extensions.hookStdoutToStderr
+'
+
+test_expect_success '`git clone` does not set extensions.hookStdoutToStderr by default' '
+	test_when_finished "rm -rf upstream repo-clone-no-ext" &&
+	git init upstream &&
+	git clone upstream repo-clone-no-ext &&
+	test_must_fail git -C repo-clone-no-ext config extensions.hookStdoutToStderr
+'
+
+test_expect_success '`git clone` respects hook.forceStdoutToStderr' '
+	test_when_finished "rm -rf upstream repo-clone" &&
+	git init upstream &&
+	test_config_global hook.forceStdoutToStderr true &&
+	git clone upstream repo-clone &&
+	git -C repo-clone config extensions.hookStdoutToStderr >actual &&
+	echo true >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'hook.forceStdoutToStderr enables extension for existing repos' '
+	test_when_finished "rm -rf remote-repo existing-repo" &&
+	git init --bare remote-repo &&
+	git init -b main existing-repo &&
+	# No local extensions.hookStdoutToStderr config set here
+	# so global config should apply
+	test_config_global hook.forceStdoutToStderr true &&
+	cd existing-repo &&
+	test_commit A &&
+	git remote add origin ../remote-repo &&
+	setup_hooks pre-push &&
+	git push origin HEAD >stdout.actual 2>stderr.actual &&
+	check_stdout_merged_to_stderr pre-push &&
+	cd ..
+'
+
+test_expect_success 'hook.forceStdoutToStderr enables pre-push parallel runs' '
+	test_when_finished "rm -rf repo-parallel" &&
+	git init --bare remote-parallel &&
+	git init repo-parallel &&
+	git -C repo-parallel remote add origin ../remote-parallel &&
+	test_commit -C repo-parallel A &&
+
+	write_script repo-parallel/.git/hooks/pre-push <<-EOF &&
+	sleep 2
+	echo "Hook 1" >&2
+	EOF
+	git -C repo-parallel config hook.hook-2.event pre-push &&
+	git -C repo-parallel config hook.hook-2.command "sleep 2; echo Hook 2 >&2" &&
+
+	git -C repo-parallel config hook.jobs 2 &&
+	git -C repo-parallel config hook.forceStdoutToStderr true &&
+
+	start=$(date +%s) &&
+	git -C repo-parallel push origin HEAD >out 2>err &&
+	end=$(date +%s) &&
+
+	duration=$((end - start)) &&
+	# Serial >= 4s, parallel < 4s.
+	test $duration -lt 4
+'
+
 test_done
-- 
2.52.0.732.gb351b5166d.dirty