Re: [PATCH v2 4/8] refs: make errno output explicit for refs_resolve_ref_unsafe

> From: Han-Wen Nienhuys <hanwen@google.com>
>
> This introduces refs_resolve_ref_unsafe_with_errno(), which makes the API
> contract for the errno output explicit. The implementation still relies on
> the global errno variable to ensure no side effects of this refactoring.
>
> In a follow-on commits, we will
>
> * migrate callers that need this error information
>
> * clear errno in refs_resolve_ref_unsafe() to make sure these other callers
> aren't using the error output accidentally.
>
> Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
> Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
> ---
>  refs.c               | 12 ++++++++++++
>  refs/refs-internal.h |  8 ++++++++
>  2 files changed, 20 insertions(+)
>
> diff --git a/refs.c b/refs.c
> index bebe3f584da7..64e2d55adcfb 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -1781,6 +1781,18 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
>  	return NULL;
>  }
>  
> +const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
> +					       const char *refname,
> +					       int resolve_flags,
> +					       struct object_id *oid,
> +					       int *flags, int *failure_errno)
> +{
> +	const char *result = refs_resolve_ref_unsafe(refs, refname,
> +						     resolve_flags, oid, flags);
> +	*failure_errno = errno;
> +	return result;
> +}
> +
>  /* backend functions */
>  int refs_init_db(struct strbuf *err)
>  {
> diff --git a/refs/refs-internal.h b/refs/refs-internal.h
> index 904b2a9e51ae..eb97023658f8 100644
> --- a/refs/refs-internal.h
> +++ b/refs/refs-internal.h
> @@ -153,6 +153,14 @@ int refs_read_raw_ref(struct ref_store *ref_store,
>  		      const char *refname, struct object_id *oid,
>  		      struct strbuf *referent, unsigned int *type);
>  
> +/* Like refs_resolve_ref_unsafe, but provide access to errno code that lead to a
> + * failure. */
> +const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
> +					       const char *refname,
> +					       int resolve_flags,
> +					       struct object_id *oid,
> +					       int *flags, int *failure_errno);
> +
>  /*
>   * Write an error to `err` and return a nonzero value iff the same
>   * refname appears multiple times in `refnames`. `refnames` must be