Re: git fails with a broken pipe when one quits the pager

From: Vincent Lefevre <vincent@vinc17.net>
Date: Feb 1, 2021, 10:34 UTC
Message-ID: <20210201103429.GT623063@zira.vinc17.org>
In-Reply-To: <87o8h4omqa.fsf@evledraar.gmail.com>

On 2021-01-31 21:49:49 +0100, Ævar Arnfjörð Bjarmason wrote:

Show 13 quoted lines

> On Sun, Jan 31 2021, Vincent Lefevre wrote:
> > FYI, I already have the exit status already in my prompt (the above
> > commands were just for the example). Still, the git behavior is
> > disturbing.
> >
> > Moreover, this doesn't solve the issue when doing something like
> >
> >   git log && some_other_command
> 
> What issue? That we're returning an exit code per getting a SIGHUP here
> is a feature. Consider:
> 
>     git -c core.pager=/bin/false log && echo showed you the output

If the pager exists with a non-zero exit status, it is normal to return a non-zero exit status. This was not the bug I reported.

> > No! I want to be warned about real SIGPIPEs.
> 
> Not being able to write "git log" output is a real SIGPIPE.

Which is not the case here, because the full output has never been requested by the user.

Show 9 quoted lines

> Is it because in your mind it's got something to do with the "|" shell
> piping construct? The SIGPIPE is sent by the kernel, so it's no less
> expected in cases like:
> 
>     git log && echo foo
> 
> Than:
> 
>     git log | cat

See the difference (without the patch) between

$ git log && echo foo; echo $? 141

and

$ git log | head; echo $? [...] 0

[...]

> Maybe we have users who'd like to work around zsh's "setopt
> PRINT_EXIT_VALUE" mode (would you want this patch if you could make zsh
> ignore 141?).

zsh is working as expected, and as I've already said, I ***WANT*** SIGPIPE to be reported by the shell, as it may indicate a real failure in a script. BTW, I even have a script using git that relies on that:

{ git rev-list --author "$@[-1]" HEAD &&
  git rev-list --grep   "$@[-1]" HEAD } | \
  git "${@[1,-2]:-lv}" --no-walk --stdin

return $((pipestatus[2] ? pipestatus[2] : pipestatus[1]))

Here it is important not to lose any information. No pager is involved, the full output is needed. If for some reason, the LHS of the pipe fails due to a SIGPIPE but the right hand side succeeds, the error will be reported.

The fact is that with a pager, the SIGPIPE with a pager is normal. Thus with a pager, git is reporting a spurious SIGPIPE, and this is disturbing.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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