Git hook's stderr is being swallowed

[wilbaker]

• I was not able to find an open or closed issue matching what I'm seeing

Setup

• Which version of Git for Windows are you using? Is it 32-bit or 64-bit?

$ git --version --build-options

git version 2.22.0.vfs.1.1
cpu: x86_64
built from commit: 58ad01641f80fac5d3468f2b9edd311bfc07f82e
sizeof-long: 4
sizeof-size_t: 8

• Which version of Windows are you running? Vista, 7, 8, 10? Is it 32-bit or 64-bit?

$ cmd.exe /c ver

Windows 10 Preview, 64bit

• What options did you set as part of the installation? Or did you choose the
  defaults?

# One of the following:
> type "C:\Program Files\Git\etc\install-options.txt"
> type "C:\Program Files (x86)\Git\etc\install-options.txt"
> type "%USERPROFILE%\AppData\Local\Programs\Git\etc\install-options.txt"
$ cat /etc/install-options.txt

Editor Option: VIM
Custom Editor Path:
Path Option: Cmd
SSH Option: OpenSSH
CURL Option: OpenSSL
CRLF Option: CRLFCommitAsIs
Bash Terminal Option: MinTTY
Performance Tweaks FSCache: Enabled
Use Credential Manager: Enabled
Enable Symlinks: Disabled
Enable Builtin Interactive Add: Disabled

• Any other interesting things about your environment that might be related
  to the issue you're seeing?

No

Details

• Which terminal/shell are you running Git from? e.g Bash/CMD/PowerShell/other

CMD

• What commands did you run to trigger this issue? If you can provide a
  Minimal, Complete, and Verifiable example
  this will help us understand the issue.

This issue is reproducible with VFS for Git's (https://github.com/Microsoft/VFSForGit) pre and post command hooks. It happens with any git command.

• What did you expect to occur after running these commands?

I expected that messages written by the hooks to stderr would be visible on the command line.

• What actually happened instead?

The hook's stderr was swallowed.

@dscho mentioned the following as a possible root cause:

When redirecting stdout to stderr in run_command(), we apparently use dup2(2, 1) (but only on Windows), which AFAICT closes 2 (i.e. stderr).

[rimrul]

When redirecting stdout to stderr in run_command(), we apparently use dup2(2, 1) (but only on Windows), which AFAICT closes 2 (i.e. stderr).

That shouldn't happen. The man page says

int dup2(int oldfd, int newfd);

[…]

dup2() makes newfd be the copy of oldfd, closing newfd first if necessary

This should close newfd aka 1 aka stdout.

[dscho]

@wilbaker I lost track: did we determine in an offline chat that this ticket could be closed, or do I misremember?

[wilbaker]

@dscho I'm having trouble remember as well, I can close this for now and re-open if I see this issue again (and determine it's something on the git side).