Re: rev-parse: -- is sometimes a flag and sometimes an arg?

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 20, 2022, 22:59 UTC
Message-ID: <xmqq8rniikrg.fsf@gitster.g>
In-Reply-To: <CAO_RewbD+BJd1hPKCmCNM8wYBSUmZ2TuOoy6t1up1CT-rbn4DA@mail.gmail.com>

Tim Hockin <thockin@google.com> writes:

Show 33 quoted lines

> ```
> $ git rev-parse unknown-tag
> unknown-tag
> fatal: ambiguous argument 'unknown-tag': unknown revision or path not
> in the working tree.
> Use '--' to separate paths from revisions, like this:
> 'git <command> [<revision>...] -- [<file>...]'
> ```
>
> OK
>
> ```
> $ git rev-parse unknown-tag --
> fatal: bad revision 'unknown-tag'
> ```
>
> Much nicer error.  But:
>
> ```
> $ git rev-parse HEAD --
> 113a928239196d0d9f70671517ce917071ceecf6
> --
> ```
>
> That's not very nice.  Why is "--" treated as an arg?
>
> ```
> $ git rev-parse HEAD
> 113a928239196d0d9f70671517ce917071ceecf6
> ```
>
> Looking at rev-parse code it SEEMS to be intentional, but I can't
> comprehend why.

Because the first function of "rev-parse" (among many others) is to be a helper usable in scripted Porcelains to "parse" command line arguments, shifting them into revs and "files". Without options like --revs-only, --no-revs, --flags etc., it dumps everything, while translating "revs" into raw object names, to its output. "--" is a valid command line option for whatever scripted Porcelain you'd be writing using "rev-parse" to help parsing its command line arguments.

So everything we see above is very much working as designed.