Dmitry Gutov <dmitry@gutov.dev> writes:
> On 05/10/2023 19:19, Spencer Baugh wrote:
>>> Could you mention which code calls 'registered' on a directory,
>>> though? If it's in-tree, that's probably a bug too.
>> vc-root-diff.  Here's the trace:
>> * vc-hg-registered("~/test-hg-repos/empty/")
>>    apply(vc-hg-registered "~/test-hg-repos/empty/")
>>    vc-call-backend(Hg registered "~/test-hg-repos/empty/")
>>    #f(compiled-function (b) #<bytecode -0x10c889a4506dd5b1>)(Hg)
>>    mapc(#f(compiled-function (b) #<bytecode -0x10c889a4506dd5b1>) (FE RCS CVS SVN SCCS SRC Bzr Git Hg))
>>    vc-registered("~/test-hg-repos/empty/")
>>    vc-backend("~/test-hg-repos/empty/")
>>    vc-working-revision("~/test-hg-repos/empty/")
>>    vc-root-diff(nil t)
>>    funcall-interactively(vc-root-diff nil t)
>>    call-interactively(vc-root-diff nil nil)
>>    command-execute(vc-root-diff)
>
> Huh, it actually looks like that call is unnecessary (the result is
> unused). These lines just come from 2009, mostly unchanged:
>
> diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
> index d3e53858c16..e3b1f7fafda 100644
> --- a/lisp/vc/vc.el
> +++ b/lisp/vc/vc.el
> @@ -2086,7 +2086,7 @@ vc-root-diff
>      (vc-maybe-buffer-sync not-urgent)
>      (let ((backend (vc-deduce-backend))
>  	  (default-directory default-directory)
> -	  rootdir working-revision)
> +	  rootdir)
>        (if backend
>  	  (setq rootdir (vc-call-backend backend 'root default-directory))
>  	(setq rootdir (read-directory-name "Directory for VC root-diff: "))
> @@ -2094,14 +2094,13 @@ vc-root-diff
>  	(if backend
>  	    (setq default-directory rootdir)
>  	  (error "Directory is not version controlled")))
> -      (setq working-revision (vc-working-revision rootdir))
>        ;; relative to it.  Bind default-directory to the root directory
>        ;; here, this way the *vc-diff* buffer is setup correctly, so
>        ;; relative file names work.
>        (let ((default-directory rootdir))
>          (vc-diff-internal
> -         t (list backend (list rootdir) working-revision) nil nil
> +         t (list backend (list rootdir)) nil nil
>           (called-interactively-p 'interactive))))))
>
>  ;;;###autoload

Yes, I would be quite happy with deleting these unused lines.  Although
I expect it's still nice to have the same optimization that vc-git does.

BTW, here's a version of my patch which follows vc-git and just returns
nil for directories.