Re: Why does git-grep appear to treat exclude pathspecs differently?

From: Jeff King <peff@peff.net>
Date: Aug 2, 2025, 09:46 UTC
Message-ID: <20250802094657.GG3711639@coredump.intra.peff.net>
In-Reply-To: <CALnO6CDNDfx6L7CmPwE0eBZFkd_JkZf6hDwrADccAb14QhJGDg@mail.gmail.com>

On Wed, Jul 30, 2025 at 05:49:29PM -0400, D. Ben Knoble wrote:

Show 19 quoted lines

> which eventually dies as noted. However:
> 
> - looks_like_pathspec() only checks for long magic, as you noted
> - setup.c:check_filename() looks for short-magic, too, but only
> considers ":^" to work like a pathname if we're excluding everything?
> 
> I think what I find confusing is that, while this is definitely a DWIM
> case for git-grep, it doesn't seem to do DWIM :) We are verifying that
> the remaining arguments are filenames, but couldn't they really be
> full pathspecs, as long as they aren't revisions?
> 
> The difference for "^:<path>" from ":^:<path>", just to complete the
> story, is that in setup.c:check_filename() we try to stat whatever
> comes after ":^":
> - for the former, that's <path> and we are ok
> - for the latter, that's :<path>, fail.
> 
> So it seems like the places that check for short-magic should also
> consider the optional trailing colon?

Yeah, I'd think so. But it's worse than that, even. According to the glossary definition you showed:

  In the short form, the leading colon `:` is followed by zero or more
  "magic signature" letters (which optionally is terminated by another
  colon `:`)

we allow multiple bits of magic. So the code in check_filename() that looks for ":/", ":^", etc would be fooled when seeing more than one character, like: ":/^exclude-from-root". AFAICT there are only two short magic types, so I guess nobody has really run into this before.

Also, I guess this function ought to be respecting the literal_pathspecs global? The actual pathspec parser does.

If we can, we probably ought to be feeding the paths to a function like pathspec.c:parse_element_magic() and then checking the resulting flags (and skipping past the prefix as it indicates).

-Peff

PS I didn't even know that we allowed multiple short items or a trailing
   colon until your email! Hidden corners of Git.