pre-push hooks and stdout regression

Hello --

   I'm one of the current maintainers of the Git LFS project, and we
happened to notice that a recent change in Git's "master" branch has
introduced a regression in our test suite.

   Specifically, with commit 3e2836a742d8b2b2da25ca06e9d0ac3a539bd966
("transport: convert pre-push to hook API") from the "ar/run-command-hook"
merged last week, it appears that when a pre-push hook such as our
git-lfs-pre-push program runs, messages it writes to its standard output
are now delivered to the user's standard error stream instead of
their standard output stream.

   I suspect this is because the pick_next_hook() function in hook.c
sets the stdout_to_stderr flag for its "cb" child_process argument,
and that function is now used to run the pre-push hook.

   Arguably, the Git LFS pre-push hook program should write its
progress meter messages to stderr, but since at least 2017 it appears
we have used stdout for this purpose:

https://github.com/git-lfs/git-lfs/commit/d665f7d725150761fe3b196da2c2d4448f7d2c61 https://github.com/git-lfs/git-lfs/pull/2732

   We can certainly work around this change in the Git LFS test suite,
since our progress messages are still output by Git, just to stderr
instead of stdout.

   However, I think there remains the larger concern that users who
depend on the existing Git pre-push behaviour in some way may also
encounter regressions, perhaps because they expect (as our test suite
does) to see certain messages either output or not output to stderr
during a Git push operation.

   Please do let me know your thoughts on this subject!  If the
consensus is that the new behaviour is correct, we'll adjust our test
suite to match it, but I'll wait to hear the outcome of any discussion
before making that change.

   Thank you again and all the best,

Chris.