Re: segfault on invalid 'git grep' invocation

On Mon, Jun 28 2021, Matthew Hughes wrote:

Hi all,

It's my first time writing to this mailing list, so apologies in advance
for any mistakes/faux pas.

Thanks a lot for the report, and welcome.

Summary
=======

Segfault seen when running:

    $ ./git grep --and -e 'pattern' -- not_a_path

Expected Behaviour
==================

The above invocation doesn't appear particularly valid to me, I
accidentally ran it while editing a command. Not sure if this needs
addressing, but perhaps the expected behaviour would be an error message
about it not being valid?

Compare with, running without '--':

    $ ./git grep --and -e 'pattern' not_a_path
    fatal: ambiguous argument 'not_a_path': unknown revision or path not in the working tree.
    Use '--' to separate paths from revisions, like this:
    'git <command> [<revision>...] -- [<file>...]'

Running with a valid path:

    $ ./git grep --and -e 'pattern' -- common-main.c
    fatal: Not a valid grep expression

    $ ./git grep --and -e 'pattern' common-main.c
    fatal: Not a valid grep expression

The exact segfault you've found is found at least back to Git version
2.0.0, so it's been with us for a while.

The problem is that you're trying to --and two things, but did not
provide two things. We apparently never checked for this, and then
segfault in the cleanup, thinking an --and must imply that we have two
sides.

I haven't looked deeply, but think that the reason it segfaults just
with not_a_path is that we then proceed to die() in something that
should probably be a BUG() instead as we can't grep in the
expected-but-not-there pattern at runtime.

Giving it a pathspec that doesn't exist means we never run the "real"
grep, but we do run the cleanup, hence the segfault.