bug#62693: 28.2; VC: CVS: Fix lost file reporting and enable reverting it

[Eli Zaretskii <eliz@gnu.org>]

> From: Olivier Certner <ocert.dev@free.fr>
> Cc: 62693@debbugs.gnu.org
> Date: Mon, 17 Apr 2023 11:24:26 +0200
> 
> > The patch is AFAICS basically a complete rewrite of an important
> > function, so I don't see how I could agree applying this to the
> > release branch.  Sorry.  (Was the introduction of so many CL-isms
> > really necessary, btw?)
> 
> This paragraph leaves me astonished.
> 
> First, because it is wrong: `vs-cvs-parse-root' is not a major function, it is 
> a very minor one.

I should have said "non-trivial".  Sorry for potentially confusing
selection of words.

> Second, because "Was the introduction of so many CL-isms really necessary, 
> btw?" is both unproductive and rude, and as such doubly inappropriate.

Dmitry asked whether it was okay to install this on the release
branch, which is currently undergoing pretest.  So I looked at the
changes from the POV of the potential for unintended consequences and
regressions.  This job is much harder when the code is thoroughly
rewritten, let alone uses a different macro system and style.  That is
why I asked the question: I presume that if the changes were less
radical, they could perhaps have been deemed appropriate for the
release branch, or at least the chances for that were higher.

> If 
> there is a policy of banishing CL forms, then say so, and even better, write 
> it in the documentation. If there is already one (I'm not aware of any), then 
> point me to it. You even didn't bother naming the constructs you're 
> questioning. So let me review all candidates for you. The "so many" (!) CL-
> isms are of 3 kinds only: `cl-defun', `cl-labels' and `cl-ecase'. The first is 
> used to bail out early from the function without complicating code. It is much 
> more appropriate from a language point of view than the `throw'/`catch' it 
> expands to (to readers, and implementors as well if at some point Emacs gains 
> true lexical non-local exits). The second fills an Emacs Lisp gap (definition 
> of internal recursive functions), so is necessary (unless you want me to 
> define these functions with `defun' whereas they are only internal and not 
> meant to be called standalone, or use `let' with `lambda` forms and 
> funcalls?). The third is the most concise way to express the intent, even 
> before `pcase'. Sure, I could use the latter and define a catch-all case with 
> an internal error, but then I'll have to do that the 4 times `cl-ecase' is 
> used: 4 additional lines with no added value. Does using `cl-ecase' really 
> change the face of Emacs world?
> 
> To be frank, I'm quite worried that I have to explain all that to an Emacs 
> maintainer.

You didn't have to.  That's not why I asked the question.

> I find "file name" or "directory name" even worse because they are ambiguous. 
> So I've settled on using "pathname" instead (the (UNIX/Windows) "path" to some 
> file, not just the filename (i.e., no slashes)). Is that OK for you?

Not really, but that's a minor point.  We can always fix the
terminology later.

Thanks.