Re: [PATCH] describe: output tag's ref instead of embedded name

[Jeff King <peff@peff.net>]

On Sat, Feb 15, 2020 at 06:34:13PM -0300, Matheus Tavares wrote:

> If a tag describes a commit, we currently output not the tag's ref but
> its embedded name. This means that when the tag is locally stored under
> a different name, the output given cannot be used to access the tag in
> any way. A warning is also emitted in this case, but the message is not
> very enlightening:
> 
> $ git tag -am "testing tag body" testing-tag
> $ mv .git/refs/tags/testing-tag .git/refs/tags/testing-tag-with-new-name
> $ git describe --tags --abbrev=0
> warning: tag 'testing-tag' is really 'testing-tag-with-new-name' here
> testing-tag
> 
> Let's make git-describe output the tag's local name instead and
> rephrase the warning to reflect the situation a little better.

Thanks. I had this on my "eh, we should probably do it before we forget"
pile, so I was quite happy to see that somebody had already handled it. :)

I think the conversion of the die() to warning() makes sense here. Do we
want to cover that with a test?

> Since the embedded name will no longer be needed for correct output, we
> can convert the die() call in append_name() when a tag doesn't have the
> embedded name to a warning(). Also, this function will now have two
> disconnected responsibilities: verifying if the tag's embedded name
> matches the ref and actually appending the ref to a given buffer (which
> does not depend on the parsed tag object itself). Thus, to increase
> intelligibility, let's make the function specialize in the former and do
> the latter outside it.

Pulling the buffer append out of the function makes a lot of sense as
well. I was puzzled at first that this old code:

> -
> -	if (n->tag) {
> -		if (all)
> -			strbuf_addstr(dst, "tags/");
> -		strbuf_addstr(dst, n->tag->tag);
> -	} else {
> -		strbuf_addstr(dst, n->path);
> -	}
>  }

...used "tags/" for "--all", but the new code doesn't:

> @@ -313,7 +305,8 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
>  		/*
>  		 * Exact match to an existing ref.
>  		 */
> -		append_name(n, dst);
> +		verify_tag_embedded_name(n);
> +		strbuf_addstr(dst, n->path);

But that makes sense. As the else clause in the old code shows, our
n->path is already set up correctly. So not only are we splitting out
the "append" concern, but we're able to make it simpler. Good.

> diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
> index 09c50f3f04..d34c091e0b 100755
> --- a/t/t6120-describe.sh
> +++ b/t/t6120-describe.sh
> @@ -129,9 +129,9 @@ test_expect_success 'rename tag A to Q locally' '
>  	mv .git/refs/tags/A .git/refs/tags/Q
>  '
>  cat - >err.expect <<EOF
> -warning: tag 'A' is really 'Q' here
> +warning: tag 'Q' is externally known as 'A'
>  EOF
> -check_describe A-* HEAD
> +check_describe Q-* HEAD
>  test_expect_success 'warning was displayed for Q' '
>  	test_i18ncmp err.expect err.actual

And this test change makes sense. I had to look up how check_describe
works, but that first argument is the expected output.

So the whole thing looks good to me, with or without the die/warning
test I mentioned above.

-Peff