bug#59014: 29.0.50; single string in function body should act as doc string

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

>> From: Nicolas Graner <nicolas@graner.name>
>> Date: Fri, 04 Nov 2022 13:26:22 +0100
>> 
>> According to the Emacs lisp manual, node "Documentation Strings of Functions":
>> 
>>     You may wonder how the documentation string could be optional, since
>>     there are required components of the function that follow it (the
>>     body). Since evaluation of a string returns that string, without any
>>     side effects, it has no effect if it is not the last form in the
>>     body. Thus, in practice, there is no confusion between the first
>>     form of the body and the documentation string; if the only body form
>>     is a string then it serves both as the return value and as the
>>     documentation.

Boy, I should (re)read this manual more regularly.  I was convinced the
intended behavior was to treat (defun f () "foo") as a function with no
docstring (as witnessed in the resulting behavior I implemented).

> Stefan, this seems to be due to your changes in commit
> 39e8fd357dd0a1f3776c05eee2cc5be451686712.  Specifically, the new
> function-documentation returns nil in this case.  Could you please
> take a look at this?

Will do,


        Stefan