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>]

>>> The problem is that with Helm completion I have an extra unknown
>>> symbol on top of list when I start typing (this is expected when
>>> require-match is non-nil),
>> Could you characterize this "unknown symbol" a bit more?  I'm having
>> trouble guessing why/how/where `confirm` would have such an effect.
> In Helm, if require-match is 'confirm, when you write in minibuffer something
> that doesn't match one of the candidates this string is appended on top
> of list and is prefixed (with display prop) with [?]. By contrast when
> require-match is nil nothing is appended on top of list and pressing RET
> doesn't exit minibuffer (helm-buffer is empty in such case).
> IOW the behavior of require-match is the same than with vanilla Emacs.

I see.  So IIUC every piece works "correctly", but since it's *very*
rare to want to use this ?-prefixed option in the case of
`describe-function`, it looks/feels like a bug.

The core of the problem is that in the normal UI, `confirm` is very
lightweight (you'll basically only notice it when you do try to enter
the name of a function that's not defined) whereas in the Helm UI it's
harder to hide it.

And I guess for other cases (like `find-file`) the use of the ?-prefixed
option is sufficiently common to deserve being more visible?



        Stefan