Re: [PATCH 1/2] t9832,t2200: avoid using pipes in git commands

>
> On Sat, Oct 17, 2020 at 12:02 PM Amanda Shafack via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> > When the upstream of a pipe throws an error, the downstream still
> > executes normally. This happens because the exit code of the upstream
> > in a pipe is ignored. This behavior can make debugging very hard
> > incase a test fails.
>
> To be more precise, we're not worried about difficulty of debugging
> when a Git command is upstream in a pipe. What we are more concerned
> with is that an unexpected failure of the Git command will go
> unnoticed (unless it also happens to produce wrong output which is
> later caught somewhere downstream). By avoiding placing Git upstream
> in a pipe, we can actively catch a failure of the Git command. The
> commit message should focus on that reason instead.
>
> > Also, pipes are prone to deadlocks. If the
> > upstream gets full, the commands downstream will never start.
>
> I don't think this is ever an issue in Git tests, so talking about it
> here probably only muddies the waters, thus makes the commit message
> less precise and more hand-wavy. Dropping this sentence is
> recommended.
>
> > Commit c6f44e1da5 (t9813: avoid using pipes, 2017-01-04) noticed that
> > the exit code of upstream in the pipe is ignored, thus using pipes
> > should be avoided.
>
> There are a lot of commits in the project history which perform this
> sort of transformation, so it's not clear to the reader why this
> particular commit is called out as being important. If it's not, then
> I'd recommend dropping this sentence, as well.
>
> > diff --git a/t/t2200-add-update.sh b/t/t2200-add-update.sh
> >  test_expect_success '"add -u non-existent" should fail' '
> >         test_must_fail git add -u non-existent &&
> > -       ! (git ls-files | grep "non-existent")
> > +       ! (
> > +               git ls-files >actual &&
> > +               grep "non-existent" actual
> > +       )
> >  '
>
> This transformation appears to be incorrect. See my review of patch
> [2/2] for details.
>
> > diff --git a/t/t9832-unshelve.sh b/t/t9832-unshelve.sh
> > @@ -68,7 +68,8 @@ EOF
> > -               git show refs/remotes/p4-unshelved/$change | grep -q "Further description" &&
> > +               git show refs/remotes/p4-unshelved/$change >actual &&
> > +               grep -q "Further description" actual &&
>
> This transformation looks fine.