Re: [PATCH v2 0/3] nd/clear-gitenv-upon-use-of-alias

[Duy Nguyen <pclouds@gmail.com>]

On Wed, Dec 23, 2015 at 4:37 PM, Jeff King <peff@peff.net> wrote:
> On Tue, Dec 22, 2015 at 10:13:03AM -0800, Junio C Hamano wrote:
>
>> > Another by the way, this "forcing aliases as external commands" now
>> > shows something like "error: git-log died of signal 13" when the pager
>> > exits early, for an alias like "l1 = log --oneline".
>>
>> ... and we do not show that when we directly call "git log" is...?
>>
>> We do signal this with non-zero exit status like so:
>>
>>       $ GIT_PAGER=true git log --oneline ; echo $?
>>         141
>>
>> and it is not surprising that the one that is catching the exit
>> status of what was spawned and reporting "signal 13".
>
> This sounded very familiar. Apparently I've been running with the patch
> below for almost 3 years and never got around to re-examining it.
>
> The original discussion is in:
>
>   http://thread.gmane.org/gmane.comp.version-control.git/212630
>
> Having skimmed through the arguments there, and given that we applied
> the patch from the middle of the thread, I think this is a good change.

Yep. The new thing here is the "died of" message now also comes from
execv_dashed_external() for non-external aliases, so it can show up a
lot more often. I wasn't sure if excluding SIGPIPE in wait_and_whine
was safe. But I _guess_ it is, based on your having no problem with
the patch for a long time and the past discussion.

>
> -- >8 --
> Date: Fri, 4 Jan 2013 07:19:35 -0500
> Subject: [PATCH] avoid SIGPIPE warnings for aliases
>
> When git executes an alias that specifies an external
> command, it will complain if the alias dies due to a signal.
> This is usually a good thing, as signal deaths are
> unexpected. However, SIGPIPE is not unexpected for many
> commands which produce a lot of output; it is intended that
> the user closing the pager would kill them them via SIGPIPE.
>
> As a result, the user might see annoying messages in a
> scenario like this:
>
>   $ cat ~/.gitconfig
>   [alias]
>   lgbase = log --some-options
>   lg = !git lgbase --more-options
>   lg2 = !git lgbase --other-options
>
>   $ git lg -p
>   [user hits 'q' to exit pager]
>   error: git lgbase --more-options died of signal 13
>   fatal: While expanding alias 'lg': 'git lgbase --more-options': Success
>
> Many users won't see this, because we execute the external
> command with the shell, and a POSIX shell will silently
> rewrite the signal-death exit code into 128+signal, and we
> will treat it like a normal exit code. However, this does
> not always happen:
>
>   1. If the sub-command does not have shell metacharacters,
>      we will skip the shell and exec it directly, getting
>      the signal code.
>
>   2. Some shells do not do this rewriting; for example,
>      setting SHELL_PATH set to zsh will reveal this problem.
>
> This patch squelches the message, and lets git exit silently
> (with the same exit code that a shell would use in case of a
> signal).
>
> The first line of the message comes from run-command's
> wait_or_whine. To silence that message, we remain quiet
> anytime we see SIGPIPE.
>
> The second line comes from handle_alias itself. It calls
> die_errno whenever run_command returns a negative value.
> However, only -1 indicates a syscall error where errno has
> something useful (note that it says the useless "success"
> above). Instead, we treat negative returns from run_command
> (except for -1) as a normal code to be passed to exit.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  git.c         | 2 +-
>  run-command.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/git.c b/git.c
> index 6ed824c..34a18a3 100644
> --- a/git.c
> +++ b/git.c
> @@ -252,7 +252,7 @@ static int handle_alias(int *argcp, const char ***argv)
>                         alias_argv[argc] = NULL;
>
>                         ret = run_command_v_opt(alias_argv, RUN_USING_SHELL);
> -                       if (ret >= 0)   /* normal exit */
> +                       if (ret != -1)  /* normal exit */
>                                 exit(ret);
>
>                         die_errno("While expanding alias '%s': '%s'",
> diff --git a/run-command.c b/run-command.c
> index 13fa452..694a6ff 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -245,7 +245,7 @@ static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
>                 error("waitpid is confused (%s)", argv0);
>         } else if (WIFSIGNALED(status)) {
>                 code = WTERMSIG(status);
> -               if (code != SIGINT && code != SIGQUIT)
> +               if (code != SIGINT && code != SIGQUIT && code != SIGPIPE)
>                         error("%s died of signal %d", argv0, code);
>                 /*
>                  * This return value is chosen so that code & 0xff
> --
> 2.7.0.rc2.368.g1cbb535
>



-- 
Duy