Re: [PATCH v4 3/4] refs: parse and use the reference storage payload

> The previous commit extended the 'extensions.refStorage' config to add
> support for a reference storage payload. The payload provides backend
> specific information on where to store references for a given directory.
> 
> Propagate this information to individual backends when initializing them
> via the 'init()' function. Both the files and reftable backends will
> parse the information to be filesystem paths to store references.
> 
> To enable this, provide a 'refs_compute_filesystem_location()' function
> which will parse the current 'gitdir' and the 'payload' to provide the
> final reference directory and common reference directory (if working in
> a linked worktree).
> 
> Finally, for linked worktrees, traditionally references were stored in
> the '$GIT_DIR/worktrees/<wt_id>' path. But when using an alternate
> reference storage path, it doesn't make sense to store main worktree
> references in the new path, and linked worktree references in the
> $GIT_DIR path. So, let's store linked worktree references in
> '$ALTERNATE_REFERENCE_DIR/worktrees/<wt_id'. To do this, create the

> diff --git a/Documentation/config/extensions.adoc b/Documentation/config/extensions.adoc
> index 532456644b..df86da6aa7 100644
> --- a/Documentation/config/extensions.adoc
> +++ b/Documentation/config/extensions.adoc
> @@ -57,10 +57,24 @@ For historical reasons, this extension is respected regardless of the
>  `core.repositoryFormatVersion` setting.
>  
>  refStorage:::
> -	Specify the ref storage format to use. The acceptable values are:
> +	Specify the ref storage format and location to use. The value can be
> +	either a format name or a URI:
>  +
>  --
> +* A format name alone (e.g., `reftable` or `files`) uses the default
> +  location (the repository's common directory).
> +
> +* A URI format `<format>://<location>` explicitly specifies both the

> diff --git a/builtin/worktree.c b/builtin/worktree.c
> index fbdaf2eb2e..800a376ac5 100644
> --- a/builtin/worktree.c
> +++ b/builtin/worktree.c
> @@ -425,6 +425,40 @@ static int make_worktree_orphan(const char * ref, const struct add_opts *opts,
>  	return run_command(&cp);
>  }
>  
> +/*
> + * References for worktress are generally stored in '$GIT_DIR/worktrees/<wt_id>'.
> + * But when using alternate reference directories, we want to store the worktree
> + * references in '$ALTERNATE_REFERENCE_DIR/worktrees/<wt_id>'.
> + *
> + * Create the necessary folder structure to facilitate the same. But to ensure
> + * that the former path is still considered a Git directory, add stubs (similar
> + *  to how we do in the reftable backend).
> + */

> diff --git a/refs.c b/refs.c
> index 32b4edaf2d..c1d69082a9 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -2224,7 +2225,11 @@ static struct ref_store *ref_store_init(struct repository *repo,
>  	if (!be)
>  		BUG("reference backend is unknown");
>  
> -	refs = be->init(repo, gitdir, flags);
> +	/*
> +	 * TODO Send in a 'struct worktree' instead of a 'gitdir', and
> +	 * allow the backend to handle how it wants to deal with worktrees.
> +	 */

> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index 240d3c3b26..160ecb53b7 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -106,19 +106,24 @@ static void clear_loose_ref_cache(struct files_ref_store *refs)
>   * set of caches.
>   */
>  static struct ref_store *files_ref_store_init(struct repository *repo,
> +					      const char *payload,
>  					      const char *gitdir,
>  					      unsigned int flags)
>  {
>  	struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
>  	struct ref_store *ref_store = (struct ref_store *)refs;
> -	struct strbuf sb = STRBUF_INIT;
> +	struct strbuf ref_common_dir = STRBUF_INIT;
> +	struct strbuf refdir = STRBUF_INIT;
> +	bool is_worktree;
> +
> +	refs_compute_filesystem_location(gitdir, payload, &is_worktree, &refdir,
> +					 &ref_common_dir);
>  
> -	base_ref_store_init(ref_store, repo, gitdir, &refs_be_files);
> +	base_ref_store_init(ref_store, repo, refdir.buf, &refs_be_files);
>  	refs->store_flags = flags;
> -	get_common_dir_noenv(&sb, gitdir);
> -	refs->gitcommondir = strbuf_detach(&sb, NULL);
> +	refs->gitcommondir = xstrdup(ref_common_dir.buf);

>  	refs->packed_ref_store =
> -		packed_ref_store_init(repo, refs->gitcommondir, flags);
> +		packed_ref_store_init(repo, payload, ref_common_dir.buf, flags);
>  	refs->log_all_ref_updates = repo_settings_get_log_all_ref_updates(repo);
>  	repo_config_get_bool(repo, "core.prefersymlinkrefs", &refs->prefer_symlink_refs);