Function backend_for

refs/reftable-backend.c:219–285

* Some refs are global to the repository (refs/heads/{*}), while others are * local to the worktree (eg. HEAD, refs/bisect/{*}). We solve this by having * multiple separate databases (ie. multiple reftable/ directories), one for * the shared refs, one for the current worktree refs, and one for each * additional worktree. For reading, we merge the view of both the shared and * the current work

 * those references in their normalized form.
 */
static int backend_for(struct reftable_backend **out,
		       struct reftable_ref_store *store,
		       const char *refname,
		       const char **rewritten_ref,
		       int reload)
{
	const char *wtname;
	int wtname_len;
	int ret;

	if (!refname) {
		*out = &store->main_backend;
		ret = 0;
		goto out;
	}

	switch (parse_worktree_ref(refname, &wtname, &wtname_len, rewritten_ref)) {
	case REF_WORKTREE_OTHER: {
		static struct strbuf wtname_buf = STRBUF_INIT;

		/*
		 * We're using a static buffer here so that we don't need to
		 * allocate the worktree name whenever we look up a reference.
		 * This could be avoided if the strmap interface knew how to
		 * handle keys with a length.
		 */
		strbuf_reset(&wtname_buf);
		strbuf_add(&wtname_buf, wtname, wtname_len);

		/*
		 * There is an edge case here: when the worktree references the
		 * current worktree, then we set up the stack once via
		 * `worktree_backends` and once via `worktree_backend`. This is
		 * wasteful, but in the reading case it shouldn't matter. And
		 * in the writing case we would notice that the stack is locked
		 * already and error out when trying to write a reference via
		 * both stacks.
		 */
		ret = backend_for_worktree(out, store, wtname_buf.buf);

		goto out;
	}
	case REF_WORKTREE_CURRENT:
		/*
		 * If there is no worktree stack then we're currently in the
		 * main worktree. We thus return the main stack in that case.
		 */
		if (!store->worktree_backend.stack)
			*out = &store->main_backend;
		else
			*out = &store->worktree_backend;
		ret = 0;
		goto out;
	case REF_WORKTREE_MAIN:
	case REF_WORKTREE_SHARED:
		*out = &store->main_backend;
		ret = 0;
		goto out;