On Thu, Jun 20, 2024 at 07:25:43PM +0200, Rubén Justo wrote:

When trying to execute a non-existent program from GIT_PAGER, we display
an error.  However, we also send the complete text to the terminal
and return a successful exit code.  This can be confusing for the user
and the displayed error could easily become obscured by a lengthy
text.

For example, here the error message would be very far above after
sending 50 MB of text:

    $ GIT_PAGER=non-existent t/test-terminal.perl git log | wc -c
    error: cannot run non-existent: No such file or directory
    50314363

Let's make the error clear by aborting the process and return an error
so that the user can easily correct their mistake.

This will be the result of the change:

    $ GIT_PAGER=non-existent t/test-terminal.perl git log | wc -c
    error: cannot run non-existent: No such file or directory
    fatal: unable to start the pager: 'non-existent'
    0

OK. My initial reaction was "eh, who care? execve() failing is only one
error mode, and we might see all kinds of failure modes from a missing
or broken pager".

But this:

Finally, it's worth noting that we are not changing the behavior if the
command specified in GIT_PAGER is a shell command.  In such cases, it
is:

    $ GIT_PAGER=:\;non-existent t/test-terminal.perl git log
    :;non-existent: 1: non-existent: not found
    died of signal 13 at t/test-terminal.perl line 33.

...shows what happens in those other cases, and you are making things
more consistent. So that seems reasonable to me.

The behavior change we're introducing in this commit affects two tests
in t7006, which is a good sign regarding test coverage and requires us
to address it.

The first test is 'git skips paging non-existing command'.  This test
comes from f7991f01f2 (t7006: clean up SIGPIPE handling in trace2 tests,
2021-11-21,) where a modification was made to a test that was originally
introduced in c24b7f6736 (pager: test for exit code with and without
SIGPIPE, 2021-02-02).  That original test was, IMHO, in the same
direction we're going in this commit.

Yeah, the point of f7991f01f2 was just to clean up the tests. The
modification was only documenting what Git happened to do for that case
now, and not meant as an endorsement of the behavior. ;) So I have no
problem changing it.

The second test being affected is: 'non-existent pager doesnt cause
crash', introduced in f917f57f40 (pager: fix crash when pager program
doesn't exist, 2021-11-24).  As its name states, it has the intention of
checking that we don't introduce a regression that produces a crash when
GIT_PAGER points to a nonexistent program.

This test could be considered redundant nowadays, due to us already
having several tests checking implicitly what a non-existent command in
GIT_PAGER produces.  However, let's maintain a good belt-and-suspenders
strategy; adapt it to the new world.

OK. I would also be happy to see it go. The crash was about reusing the
pager child_process struct, and no we know that cannot happen. Either we
run the pager or we immediately bail. I think that the code change in
that commit could also be reverted (to always re-init the child
process), but it's probably more defensive to keep it.

-Peff