Re: Bug or unexpected behaviour in git show <rev>:a\b

["David Burström" <davidburstrom@spotify.com>]

On Sat, 25 Jan 2020 at 01:00, Jeff King <peff@peff.net> wrote:
> > > We _could_ also say "even though this could technically be a pathspec
> > > because of its metacharacter, it looks vaguely enough like a
> > > path-in-tree revision that we shouldn't guess". That I'm less
> > > comfortable with, just because it makes the heuristics even more
> > > magical.
> >
> > Not just it becomes more magical, I am afraid that the code to
> > implement such a heuristics would be fragile and become a source of
> > unnecessary bugs.  Let's not go there.
>
> OK. It does mean that:
>
>   git show HEAD:a*
>
> will still quietly produce no output instead of saying "hey, there is no
> a* in HEAD". But I think given the lack of bug reports over the years
> that this case (and the backslash one I'm fixing) are probably
> relatively rare.  The backslash one seems a lot more likely, just
> because Windows folks may treat it like a path separator (I'm not sure
> if that even works, considering its meaning in a glob, but certainly I
> can imagine somebody doing so as an experiment and getting confused by
> the result).

I'm normally in a Unix environment but needed to address a potential
issue in Windows, which indeed
got me confused about the results.

Upon experimenting in said Unix environment with what you outlined
above on making revision and pathspec explicit,
I figured that it becomes a little odd in the case where one would use
a glob meta character in a filename (why anybody would want
that except for academic reasons is beyond me), but it could still be
a source of bugs in tooling interacting with git:

Given a repository initialized with

$ git init && echo a > a && echo '*' > '*' && git add a '*' && git
commit -m "first" && git rm a '*' && git commit -m "second"

there's a bit of a discrepancy when using git show to dump the
contents per revision. In the beginning, everything is normal for
HEAD^ but for HEAD, it's a requirement to use disambiguation to avoid
believing that '*' was an empty file. At the same time, the
disambiguation causes the error message change its nature, for obvious
reasons:

$ git show 'HEAD^:a'
a
$ git show 'HEAD^:a' --
a
$ git show 'HEAD^:*' # presumably get_oid finds the object
*
$ git show 'HEAD^:*' --
*
$ git show 'HEAD:a'
fatal: Path 'a' does not exist in 'HEAD'
$ git show 'HEAD:a' --
fatal: bad revision 'HEAD:a'
$ git show 'HEAD:*'
$ git show 'HEAD:*' --
fatal: bad revision 'HEAD:*'

Indeed, it seems to be working as designed or at least explainably.
I'll make sure to add '--' in my tool integration to deal with this
corner case.