Subject: Re: [PATCH] object-name: fix resolution of object names containing curly braces

From: Junio C Hamano <[email-masked]>
Date: Wed, 01 Jan 2025 09:00:59 -0800

"Elijah Newren via GitGitGadget" <[email-masked]> writes:

> From: Elijah Newren <[email-masked]>
>
> Given a branch name of 'foo{bar', commands like
>
>     git cat-file -p foo{bar:README.md
>
> should succeed (assuming that branch had a README.md file, of course).
> However, the change in cce91a2caef9 (Change 'master@noon' syntax to
> 'master@{noon}'., 2006-05-19) presumed that curly braces would always
> come after an '@' and be paired, causing 'foo{bar:README.md' to
> entirely miss the ':' and assume there's no object being referenced.
> In short, git would report:
>
>     fatal: Not a valid object name foo{bar:README.md
>
> Change the parsing to only make the assumption of paired curly braces
> immediately after a '@' character appears.

Interesting.  I wonder if this looseness was to ensure that we won't
mistake a colon inside "master^{/title with : a colon}" as a start
of a subpath, instead of asking for a commit with a title that
happens to have a colon in it?

> Add tests for both this and 'foo@@{...}' cases, which an initial version
> of this patch broke.

Thanks for being extra careful here.

> Reported-by: Gabriel Amaral <[email-masked]>
> Helped-by: Michael Haggerty <[email-masked]>
> Signed-off-by: Elijah Newren <[email-masked]>
> ---
>     object-name: fix resolution of object names containing curly braces
>     
>     Maintainer note: this bug dates back to 2006; it is not a regression in
>     this cycle.
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1844%2Fnewren%2Fobject-name-fix-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1844/newren/object-name-fix-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/1844
>
>  object-name.c       |  8 +++++---
>  t/t1006-cat-file.sh | 17 +++++++++++++++++
>  2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/object-name.c b/object-name.c
> index c892fbe80aa..e92f26b3256 100644
> --- a/object-name.c
> +++ b/object-name.c
> @@ -2087,12 +2087,14 @@ static enum get_oid_result get_oid_with_context_1(struct repository *repo,
>  		return -1;
>  	}
>  	for (cp = name, bracket_depth = 0; *cp; cp++) {
> -		if (*cp == '{')
> +		if (*cp == '@' && *(cp+1) == '{') {
> +			cp++;
>  			bracket_depth++;
> -		else if (bracket_depth && *cp == '}')
> +		} else if (bracket_depth && *cp == '}') {
>  			bracket_depth--;
> -		else if (!bracket_depth && *cp == ':')
> +		} else if (!bracket_depth && *cp == ':') {
>  			break;
> +		}
>  	}
>  	if (*cp == ':') {
>  		struct object_id tree_oid;
> diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh
> index d36cd7c0863..252485dac78 100755
> --- a/t/t1006-cat-file.sh
> +++ b/t/t1006-cat-file.sh
> @@ -603,6 +603,23 @@ test_expect_success FUNNYNAMES '--batch-check, -Z with newline in input' '
>  	test_cmp expect actual
>  '
>  
> +test_expect_success FUNNYNAMES 'setup with curly braches in input' '
> +	git branch "foo{bar" &&
> +	git branch "foo@"
> +'
> +
> +test_expect_success FUNNYNAMES 'object reference with curly brace' '
> +	git cat-file -p "foo{bar:hello" >actual &&
> +	git cat-file -p HEAD:hello >expect &&
> +	test_cmp expect actual
> +'
> +
> +test_expect_success FUNNYNAMES 'object reference with at-sign' '
> +	git cat-file -p "foo@@{0}:hello" >actual &&
> +	git cat-file -p HEAD:hello >expect &&
> +	test_cmp expect actual
> +'
> +
>  test_expect_success 'setup blobs which are likely to delta' '
>  	test-tool genrandom foo 10240 >foo &&
>  	{ cat foo && echo plus; } >foo-plus &&
>
> base-commit: 92999a42db1c5f43f330e4f2bca4026b5b81576f