Re: [PATCH v4 2/2] hook API: fix v2.36.0 regression: hooks should be connected to a TTY

> {pre-commit,prepare-commit-msg} hook to hook.h, 2021-12-22): Due to
> using the run_process_parallel() API in the earlier 96e7225b310 (hook:
> add 'run' subcommand, 2021-12-22) we'd capture the hook's stderr and
> stdout, and thus lose the connection to the TTY in the case of
> e.g. the "pre-commit" hook.
>
> As a preceding commit notes GNU parallel's similar --ungroup option
> also has it emit output faster. While we're unlikely to have hooks
> that emit truly massive amounts of output (or where the performance
> thereof matters) it's still informative to measure the overhead. In a
> similar "seq" test we're now ~30% faster:

>
> 	$ cat .git/hooks/seq-hook; git hyperfine -L rev origin/master,HEAD~0 -s 'make CFLAGS=-O3' './git hook run seq-hook'
> 	#!/bin/sh
>
> 	seq 100000000
> 	Benchmark 1: ./git hook run seq-hook' in 'origin/master
> 	  Time (mean ± σ):     787.1 ms ±  13.6 ms    [User: 701.6 ms, System: 534.4 ms]
> 	  Range (min … max):   773.2 ms … 806.3 ms    10 runs
>
> 	Benchmark 2: ./git hook run seq-hook' in 'HEAD~0
> 	  Time (mean ± σ):     603.4 ms ±   1.6 ms    [User: 573.1 ms, System: 30.3 ms]
> 	  Range (min … max):   601.0 ms … 606.2 ms    10 runs
>
> 	Summary
> 	  './git hook run seq-hook' in 'HEAD~0' ran
> 	    1.30 ± 0.02 times faster than './git hook run seq-hook' in 'origin/master'
>
> 1. https://lore.kernel.org/git/CA+dzEBn108QoMA28f0nC8K21XT+Afua0V2Qv8XkR8rAeqUCCZw@mail.gmail.com/
>
> Reported-by: Anthony Sottile <asottile@umich.edu>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  hook.c          |  1 +
>  t/t1800-hook.sh | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
>
> diff --git a/hook.c b/hook.c
> index 1d51be3b77a..7451205657a 100644
> --- a/hook.c
> +++ b/hook.c
> @@ -144,6 +144,7 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
>  		cb_data.hook_path = abs_path.buf;
>  	}
>
> +	run_processes_parallel_ungroup = 1;
>  	run_processes_parallel_tr2(jobs,
>  				   pick_next_hook,
>  				   notify_start_failure,
> diff --git a/t/t1800-hook.sh b/t/t1800-hook.sh
> index 26ed5e11bc8..0b8370d1573 100755
> --- a/t/t1800-hook.sh
> +++ b/t/t1800-hook.sh
> @@ -4,6 +4,7 @@ test_description='git-hook command'
>
>  TEST_PASSES_SANITIZE_LEAK=true
>  . ./test-lib.sh
> +. "$TEST_DIRECTORY"/lib-terminal.sh
>
>  test_expect_success 'git hook usage' '
>  	test_expect_code 129 git hook &&
> @@ -120,4 +121,40 @@ test_expect_success 'git -c core.hooksPath=<PATH> hook run' '
>  	test_cmp expect actual
>  '
>
> +test_hook_tty() {
> +	local fd="$1" &&
> +
> +	cat >expect &&
> +
> +	test_when_finished "rm -rf repo" &&
> +	git init repo &&
> +
> +	test_hook -C repo pre-commit <<-EOF &&
> +	{
> +		test -t 1 && echo >&$fd STDOUT TTY || echo >&$fd STDOUT NO TTY &&
> +		test -t 2 && echo >&$fd STDERR TTY || echo >&$fd STDERR NO TTY
> +	} $fd>actual
> +	EOF
> +
> +	test_commit -C repo A &&
> +	test_commit -C repo B &&
> +	git -C repo reset --soft HEAD^ &&
> +	test_terminal git -C repo commit -m"B.new" &&
> +	test_cmp expect repo/actual
> +}
> +
> +test_expect_success TTY 'git hook run: stdout and stderr are connected to a TTY: STDOUT redirect' '
> +	test_hook_tty 1 <<-\EOF
> +	STDOUT NO TTY
> +	STDERR TTY
> +	EOF
> +'
> +
> +test_expect_success TTY 'git hook run: stdout and stderr are connected to a TTY: STDERR redirect' '
> +	test_hook_tty 2 <<-\EOF
> +	STDOUT TTY
> +	STDERR NO TTY
> +	EOF
> +'

> +
>  test_done
> --
> 2.36.1.1103.g036c05811b0
>
>