Subject: Re: [PATCH 2/5] describe: error if blob not found

From: Junio C Hamano <[email-masked]>
Date: Mon, 18 Aug 2025 14:12:15 -0700

Jeff King <[email-masked]> writes:

> If describe_blob() does not find the blob in question, it returns an
> empty strbuf, and we print an empty line. This differs from
> describe_commit(), which always either returns an answer or calls die()
> itself. As the blob function was bolted onto the command afterwards, I
> think its behavior is not intentional, and it is just a bug that it does
> not report an error.

Yes, let's do so.  Silently succeeding without returning anything
useful is not what we usually do in this system.

> This one is perhaps the most controversial, as it is a change in
> behavior. But the current behavior just really seems like a bug to me.
>
> Unlike what René posted earlier, I didn't record the dst strbuf's
> original size and compare against that. This is a static function with
> only one caller that passes in an empty strbuf, so being overly
> defensive didn't seem worth it (arguably these functions should just
> return an allocated buffer anyway).

Sounds sensible.

Thanks.

> diff --git a/builtin/describe.c b/builtin/describe.c
> index 383d3e6b9a..06e413d937 100644
> --- a/builtin/describe.c
> +++ b/builtin/describe.c
> @@ -535,6 +535,9 @@ static void describe_blob(const struct object_id *oid, struct strbuf *dst)
>  	reset_revision_walk();
>  	release_revisions(&revs);
>  	strvec_clear(&args);
> +
> +	if (!dst->len)
> +		die(_("blob '%s' not reachable from HEAD"), oid_to_hex(oid));
>  }
>  
>  static void describe(const char *arg, int last_one)
> diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
> index 256ccaefb7..470631d17d 100755
> --- a/t/t6120-describe.sh
> +++ b/t/t6120-describe.sh
> @@ -409,6 +409,12 @@ test_expect_success 'describe tag object' '
>  	test_grep "fatal: test-blob-1 is neither a commit nor blob" actual
>  '
>  
> +test_expect_success 'describe an unreachable blob' '
> +	blob=$(echo not-found-anywhere | git hash-object -w --stdin) &&
> +	test_must_fail git describe $blob 2>actual &&
> +	test_grep "blob .$blob. not reachable from HEAD" actual
> +'
> +
>  test_expect_success ULIMIT_STACK_SIZE 'name-rev works in a deep repo' '
>  	i=1 &&
>  	while test $i -lt 8000