Subject: Re: Suggestion: error "tag ... already exists" should distinguish between tagging different or same commit:

From: Junio C Hamano <[email-masked]>
Date: Mon, 07 Jul 2025 15:24:29 -0700

Junio C Hamano <[email-masked]> writes:

> Or simply something like this.  I am not convinced (yet) that this
> is a good idea; I merely is showing that the implementation would
> look like this.
>
> ----- >8 -----
> Subject: tag: allow idempotent "git tag" without "--force"
>
> When "git tag T O" is told to create a tag pointing at an object O
> without the "--force" option, it refuses with "tag T already exists",
> even when T points at O (which makes it a no-op).
>
> Let's allow this "idempotent" case by special casing.
>
> Signed-off-by: Junio C Hamano <[email-masked]>
> ---
>  builtin/tag.c  |  2 +-
>  t/t7004-tag.sh | 12 +++++++++---
>  2 files changed, 10 insertions(+), 4 deletions(-)

As I see nobody biting, I am inclined to say that this is not such a
brilliant idea.  Let's chuck it.

>
> diff --git c/builtin/tag.c w/builtin/tag.c
> index 4742b27d16..5380a46494 100644
> --- c/builtin/tag.c
> +++ w/builtin/tag.c
> @@ -660,7 +660,7 @@ int cmd_tag(int argc,
>  
>  	if (refs_read_ref(get_main_ref_store(the_repository), ref.buf, &prev))
>  		oidclr(&prev, the_repository->hash_algo);
> -	else if (!force)
> +	else if (!force && (create_tag_object || !oideq(&object, &prev)))
>  		die(_("tag '%s' already exists"), tag);
>  
>  	opt.message_given = msg.given || msgfile;
> diff --git c/t/t7004-tag.sh w/t/t7004-tag.sh
> index 10835631ca..9a253a44a8 100755
> --- c/t/t7004-tag.sh
> +++ w/t/t7004-tag.sh
> @@ -126,7 +126,7 @@ test_expect_success 'annotated tag with --create-reflog has correct message' '
>  '
>  
>  test_expect_success '--create-reflog does not create reflog on failure' '
> -	test_must_fail git tag --create-reflog mytag &&
> +	test_must_fail git tag --create-reflog mytag no-such-object &&
>  	test_must_fail git reflog exists refs/tags/mytag
>  '
>  
> @@ -183,8 +183,14 @@ test_expect_success 'listing tags using a non-matching pattern should output not
>  
>  # special cases for creating tags:
>  
> -test_expect_success 'trying to create a tag with the name of one existing should fail' '
> -	test_must_fail git tag mytag
> +test_expect_success 'recreating a tag without --force' '
> +	# light-weight tag pointing at the same thing
> +	# now succeeds
> +	git tag mytag HEAD &&
> +	# light-weight tag pointing at a different thing
> +	test_must_fail git tag mytag HEAD: &&
> +	# creating annotated tag, pointing at the same object.
> +	test_must_fail git tag -a -m anno mytag $taggedobject
>  '
>  
>  test_expect_success 'trying to create a tag with a non-valid name should fail' '