Re: [PATCH 2/4] branch: add branch_checked_out() helper

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 3, 2022, 18:31 UTC
Message-ID: <xmqqzgitfvjs.fsf@gitster.g>
In-Reply-To: <5f54766e1032ebf3a331516a6dd696b997bdfdd8.1654263472.git.gitgitgadget@gmail.com>

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

Show 12 quoted lines

> +int branch_checked_out(const char *refname, char **path)
> +{
> +	struct worktree **worktrees = get_worktrees();
> +	const struct worktree *wt = find_shared_symref(worktrees, "HEAD", refname);
> +	int result = wt && !wt->is_bare;
> +
> +	if (result && path)
> +		*path = xstrdup(wt->path);
> +
> +	free_worktrees(worktrees);
> +	return result;
> +}

Don't you plan to call this repeatedly from the for_each_deco iteration? I am wondering if it should take the result of get_worktrees() and reuse the result of get_worktrees().

There also was another topic that was triggered by find_shared_symref() being relatively heavy-weight, which suggests a more involved refactoring.

I wonder if we rather want to rewrite find_shared_symref() *not* to take the target parameter at all, and instead introduce a new function that iterates over worktrees and report the branch that is checked out (or being operated on via rebase or bisect). Then we can

 - create a strset out of its result, i.e. set of branches that
   should not be touched;

 - iterate over refs that point into the history being rebased
   (using for_each_decoration()), and consult that strset to see if
   any of them is being rewritten.

With the API of find_shared_symref(), we'd need to iterate over all worktrees for each decoration. With such a restructuring, we can iterate over all worktrees just once, and match the result with decoration, so the problem becomes O(N)+O(M) and not O(N*M) for number of worktrees N and number of decorations M.