bug#64902: 30.0.50; REQUIRE-MATCH completing-read arg in describe-* commands

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

>> Having tried now I see that the command signals an error when
>> symbol-function is void.
>
> Assuming that "the command" is `describe-function` and you mean the
> argument SYMBOL of `symbol-function` is void (I hardly see why
> `symbol-function` would be void), I can't reproduce your
> error, here a small recipe:

Yes, in some cases it does "work".

> (defun advice-foo-test ()
>   (message "Hello"))
>
> (advice-add 'foo-test :override 'advice-foo-test)

Notice that even after reverting my commit, `describe-function` still
accepts (and completes) `foo-test` :-)
[ This is because it adds a `function-documentation` property.  ]

> ,----
> | foo-test is .
> | 
> | [Missing arglist.]
> | 
> | Not documented.
> `----

It doesn't signal an error, but the *Help* above is rather poor :-(


        Stefan