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

On Tue, Dec 22, 2015 at 10:13:03AM -0800, Junio C Hamano wrote:

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.

-- >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(-)