Re: [PATCH v2 2/7] branch: add branch_checked_out() helper

[Derrick Stolee <derrickstolee@github.com>]

On 6/7/2022 6:09 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> +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(), instead of
> enumerating the list of worktrees and freeing for each of the
> branches you need to inspect.

Sorry, you had mentioned this in v1 and I just forgot to fix this.

> There also was another topic
> 
> https://lore.kernel.org/git/pull.1266.v2.git.git.1652690501963.gitgitgadget@gmail.com/
> 
> 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 takes a worktree, 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.

Yes, that's a good plan. I'll take a look.

Thanks,
-Stolee