bug#72787: 31.0.50; Invalid describe-function completion candidates

[Pip Cet via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

"Eshel Yaron via \"Bug reports for GNU Emacs, the Swiss army knife of text editors\"" <bug-gnu-emacs@gnu.org> writes:

> I've stumbled upon an issue with C-h f completions, both on the release
> branch and on the master branch:
>
> 1. emacs -Q
> 2. C-h f string-edit- TAB
>
> In Emacs 29, this pops up the *Completions* buffer, with 3 completion
> candidates, string-edit-{abort,done,mode}.  That's the expected
> behavior, because "string-edit-" is not itself a valid candidate.
>
> However, in the release and master branches I get a minibuffer message
> saying "Complete, but not unique".  This is incorrect, because the input
> is not complete.  Another TAB pops up the *Completions* buffer, which is
> now showing 4 candidates: the expected 3 plus "string-edit-" itself.
> Typing RET exits the minibuffer without asking for confirmation, and
> yields an error: "Symbol’s function definition is void: string-edit-".
>
> So it seems like "string-edit-" is being considered as a valid
> completion candidate, while it shouldn't be.

This appears to be caused by commit
45ae4de0e7ce99c88c62f940f605bca693b8e33f:

* lisp/help-fns.el (help-definition-prefixes): Don't delete the hashtable

Pip