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

From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Anthony Sottile <asottile@umich.edu>,
	Emily Shaffer <emilyshaffer@google.com>,
	Phillip Wood <phillip.wood123@gmail.com>
Subject: Re: [PATCH v4 2/2] hook API: fix v2.36.0 regression: hooks should be connected to a TTY
Date: Wed, 1 Jun 2022 18:50:06 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.2206011827300.349@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <patch-v4-2.2-8ab09f28729-20220531T173005Z-avarab@gmail.com>

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Hi Ævar,

On Tue, 31 May 2022, Ævar Arnfjörð Bjarmason wrote:

> Fix a regression reported[1] in f443246b9f2 (commit: convert

The regression was not reported in f443247b9f2.

> {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:

It is an unwanted distraction to talk about the speed here, when the
entire purpose of the patch series is to fix the regression that stdio are
no longer connected when running hooks.

>
> 	$ 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
> +'

Instead of spreading the regression test out over so many lines, a single
test case that verifies what needs to be verified succinctly should be
plenty sufficient. Something along these lines:

	test_expect_success TTY 'hooks are conencted to stdio' '
		test_when_finished "rm .git/hooks/pre-commit" &&

		write_script .git/hooks/pre-commit <<-EOF
		test -t 1 && echo "stdout is a TTY" >out
		test -t 2 && echo "stderr is a TTY" >>out
		EOF

		test_terminal git commit --allow-empty -m hooks-and-stdio &&
		grep stdout out &&
		grep stderr out
	'

Not only is this much easier to review, not only is it more obvious what
is being tested, it is also much quicker to debug in case it fails.

Ciao,
Johannes

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