Subject: Re: [PATCH 2/3] refs: do not label special refs as pseudo refs

From: Phillip Wood <[email-masked]>
Date: Mon, 29 Apr 2024 16:12:37 +0100

Hi Patrick

On 29/04/2024 14:41, Patrick Steinhardt wrote:
> diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt
> index d71b199955..4275918fa0 100644
> --- a/Documentation/glossary-content.txt
> +++ b/Documentation/glossary-content.txt
> @@ -497,20 +497,28 @@ exclude;;
>   	unusual refs.
>   
>   [[def_pseudoref]]pseudoref::
> -	Pseudorefs are a class of files under `$GIT_DIR` which behave
> -	like refs for the purposes of rev-parse, but which are treated
> -	specially by git.  Pseudorefs both have names that are all-caps,
> -	and always start with a line consisting of a
> -	<<def_SHA1,SHA-1>> followed by whitespace.  So, HEAD is not a
> -	pseudoref, because it is sometimes a symbolic ref.  They might
> -	optionally contain some additional data.  `MERGE_HEAD` and
> -	`CHERRY_PICK_HEAD` are examples.  Unlike
> -	<<def_per_worktree_ref,per-worktree refs>>, these files cannot
> -	be symbolic refs, and never have reflogs.  They also cannot be
> -	updated through the normal ref update machinery.  Instead,
> -	they are updated by directly writing to the files.  However,
> -	they can be read as if they were refs, so `git rev-parse
> -	MERGE_HEAD` will work.
> +	Pseudorefs are references that live in the root of the reference
> +	hierarchy, outside of the usual "refs/" hierarchy. Pseudorefs have an
> +	all-uppercase name and must end with a "_HEAD" suffix, for example
> +	"`BISECT_HEAD`". Other than that, pseudorefs behave the exact same as
> +	any other reference and can be both read and written via regular Git
> +	tooling.

This changes the definition to allow pseudorefs to by symbolic refs. 
When is_pseudoref() was introduced Junio and I had a brief discussion 
about this restriction and he was not in favor of allowing pseudorefs to 
be symbolic refs [1].

Are there any practical implications of the changes in this patch for 
users running commands like "git log FETCH_HEAD" (I can't think of any 
off the top of my head but it would be good to have some reassurance on 
that point in the commit message)

Best Wishes

Phillip

[1] https://lore.kernel.org/git/[email-masked]/

> +<<def_special_ref>,Special refs>> are not pseudorefs.
> ++
> +Due to historic reasons, Git has several irregular pseudo refs that do not
> +follow above rules. The following list of irregular pseudo refs is exhaustive
> +and shall not be extended in the future:
> +
> + - "`AUTO_MERGE`"
> +
> + - "`BISECT_EXPECTED_REV`"
> +
> + - "`NOTES_MERGE_PARTIAL`"
> +
> + - "`NOTES_MERGE_REF`"
> +
> + - "`MERGE_AUTOSTASH`"
>   
>   [[def_pull]]pull::
>   	Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
> diff --git a/refs.c b/refs.c
> index c64f66bff9..567c6fc6ff 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -905,6 +905,8 @@ int is_pseudoref(struct ref_store *refs, const char *refname)
>   
>   	if (!is_pseudoref_syntax(refname))
>   		return 0;
> +	if (is_special_ref(refname))
> +		return 0;
>   
>   	if (ends_with(refname, "_HEAD")) {
>   		refs_resolve_ref_unsafe(refs, refname,
> diff --git a/t/t6302-for-each-ref-filter.sh b/t/t6302-for-each-ref-filter.sh
> index 948f1bb5f4..8c92fbde79 100755
> --- a/t/t6302-for-each-ref-filter.sh
> +++ b/t/t6302-for-each-ref-filter.sh
> @@ -52,6 +52,23 @@ test_expect_success '--include-root-refs pattern prints pseudorefs' '
>   	test_cmp expect actual
>   '
>   
> +test_expect_success '--include-root-refs pattern does not print special refs' '
> +	test_when_finished "rm -rf repo" &&
> +	git init repo &&
> +	(
> +		cd repo &&
> +		test_commit initial &&
> +		git rev-parse HEAD >.git/MERGE_HEAD &&
> +		git for-each-ref --format="%(refname)" --include-root-refs >actual &&
> +		cat >expect <<-EOF &&
> +		HEAD
> +		$(git symbolic-ref HEAD)
> +		refs/tags/initial
> +		EOF
> +		test_cmp expect actual
> +	)
> +'
> +
>   test_expect_success '--include-root-refs with other patterns' '
>   	cat >expect <<-\EOF &&
>   	HEAD