bug#72511: 30.0.50; prefix-completions is always nil in help--symbol-completion-table

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 72511@debbugs.gnu.org
> Date: Wed, 14 Aug 2024 11:50:47 -0400
> From:  Stefan Monnier via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> > (when help-enable-completion-autoload
> >   (let ((prefixes (radix-tree-prefixes (help-definition-prefixes) string)))
> >     (help--load-prefixes prefixes)))
> > (let ((prefix-completions
> >        (and help-enable-completion-autoload
> >             (mapcar #'intern (all-completions string definition-prefixes)))))
> >
> > By default, `help-enable-completion-autoload' is t, so this code should
> > normally run. The perceived problem here is that the definition of
> > `help-definition-prefixes' function is as follows:
> >
> > (defun help-definition-prefixes ()
> >   "Return the up-to-date radix-tree form of `definition-prefixes'."
> >   (when (> (hash-table-count definition-prefixes) 0)
> >     (maphash (lambda (prefix files)
> >                (let ((old (radix-tree-lookup help-definition-prefixes prefix)))
> >                  (setq help-definition-prefixes
> >                        (radix-tree-insert help-definition-prefixes
> >                                           prefix (append old files)))))
> >              definition-prefixes)
> >     (clrhash definition-prefixes))
> >   help-definition-prefixes)
> >
> > Because of the `clrhash', `definition-prefixes' will always be empty
> > after the function call to `help-definition-prefixes'.
> 
> Duh, indeed.
> IIRC it's a leftover from some older version of the code.
> I think the patch below is in order.

Thanks, please install on the emacs-30 branch.