Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> 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".

So in which cases does it fails?

>> (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` :-)

Yes I already noticed this ;-)

> 
> [ This is because it adds a `function-documentation` property.  ]

Ok, thanks to explain this.

>> ,----
>> | foo-test is .
>> | 
>> | [Missing arglist.]
>> | 
>> | Not documented.
>> `----
>
> It doesn't signal an error, but the *Help* above is rather poor :-(

Yes it is why now Helm adds a brief description in such case when
completions-detailed is enabled.

-- 
Thierry