Subject: bug#74420: 31.0.50; PCM completion for ~/src/emacs/trunk/*/minibuf breaks

From: Stefan Monnier <[email-masked]>
Date: Mon, 18 Nov 2024 15:39:17 -0500

> An explicitly typed * has different semantics from automatically
> inserted PCM wildcards, so it should be preserved on
> try-completion.  We already do this in some cases, but now we do
> it more.  Concretely, we do it by optimizing the PCM pattern
> more aggressively to avoid having multiple wildcards in a row:
> after those are removed, the existing code in
> completion-pcm--merge-completions is able to preserve * in more
> cases.

Oh, indeed, thank you.

The patch looks good to me, so if there are no objection, I'll install
it in a few days (feel free to ping me if I forget).
Banter follows.

> * lisp/minibuffer.el (completion-pcm--optimize-pattern): Add
> more optimizations. (bug#74420)

Aha, so that's why you didn't submit the patch together with the initial
bug report!

> -        (`(,(or 'any 'any-delim) ,(or 'any 'point) . ,_)
> -         (setq p (cdr p)))
> +        ;; Remove duplicate `any' and `prefix'
> +        (`(any any . ,rest)
> +         (setq p (cons 'any rest)))
> +        (`(prefix prefix . ,rest)
> +         (setq p (cons 'prefix rest)))
> +        ;; `any' matches anything `any-delim' does, and grows the same way.
> +        (`(any-delim any . ,rest)
> +         (setq p (cons 'any rest)))

AFAICT you can still merge the `any-delim any` and `any any` cases.

> +        ;; Remove other wildcards found around `star' or `point'.
> +        ((or `(,(and keep (or 'star 'point)) ,(or 'any 'any-delim 'prefix) . ,rest)
> +             `(,(or 'any 'any-delim 'prefix) ,(and keep (or 'star 'point)) . ,rest))
> +         (setq p (cons keep rest)))

BTW, maybe we should go with something like

       (`(,(and (pred symbolp) s1) ,(and (pred symbolp) s2) . ,rest)
        (cond ((completion-pcm--<something>-p s1 s2) (setq p (cons s1 rest)))
              ((completion-pcm--<something>-p s2 s1) (setq p (cons s2 rest)))
              (t (push (pop p) n))))

Where `completion-pcm--<something>-p` is some kind of partial ordering?

        Stefan