Subject: Re: Possible bug: Empty magic word list in pathspec is handled differently in short vs. long form

From: Junio C Hamano <[email-masked]>
Date: Wed, 19 Feb 2025 09:11:50 -0800

Anselm Schüler <[email-masked]> writes:

> If you run git diff for a pathspec with an empty magic word/symbol
> list in short form (prefixed by ::) and in long form (prefixed by
> :():), you get different results.

The short form is prefixed by a ":" and optionally ends by a ":",
but the optional termination may not be required when there is no
ambiguity (e.g. ":/!path" is "from the top, not matching "path", as
"p" cannot be a magic signature; ":/:!path" is "from the top,
matching "!path", as the set of magic signatures ends with the
second disambiguating colon).

The long form is prefixed by a ":(" and ends by a ")".

> Here’s an example use of git that illustrates this:
>
> ~☭ mkdir gittest
> ~☭ y gittest/
> ~/gittest☭ git init
> Initialized empty Git repository in /home/anselmschueler/gittest/.git/
> ~/gittest (b0)☭ uuidgen >file
> ~/gittest (b0)☭ git add file && git commit -m "$(read)"
> read> initial commit
> [b0 (root-commit) cd3bd43] initial commit
>  1 file changed, 1 insertion(+)
>  create mode 100644 file
> ~/gittest (b0)☭ uuidgen >file
> ~/gittest (b0)☭ git diff -- "::file"
>
> file
> ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
>
> ───┐
> 1: │
> ───┘
> 66d18ffa-1128-42a5-8d4e-f9d75eb86b92
> 9acea2b5-50a6-4f87-ae1a-64019a93e55e
> ~/gittest (b0)☭ git diff -- ":():file"
> ~/gittest (b0)☭

Doesn't ":():file" ask for a match for the pattern ":file", with a
leading colon?