bug#66136: 29.1; byte-compiler reports "misplaced interactive spec" with empty fct in lexical environment

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

>> Date: Thu, 21 Sep 2023 23:39:47 +0200
>> From:  Jens Schmidt via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> Found the issue I think:
>> 
>> -------------------- bad case --------------------
>> (macroexp-parse-body '("Allows interactive calls." (interactive "^P")))
>> 
>> =>
>> 
>> (("Allows interactive calls.")
>>  (interactive "^P"))
>> -------------------- bad case --------------------
>> 
>> -------------------- good case --------------------
>> (macroexp-parse-body '("Allows interactive calls." (interactive "^P") nil))
>> 
>> =>
>> 
>> (("Allows interactive calls." (interactive "^P"))
>>  nil)
>> -------------------- good case --------------------
>> 
>> That is, macroexp-parse-body does not consider the case that a body can
>> consist of declarations only and, if this is the case, puts the last
>> declaration into the body forms.
>> 
>> Could provide a patch if somebody confirms that this is really the root
>> cause of this issue.  Yet on the other hand this is pretty deep elisp,
>> so if somebody else steps forward, I'll be glad as well.
>
> Adding Stefan, in case he has comments/suggestions.

I'm in favor of requiring *something* after the declarations.
So yes, the first case above is a bug and should be fixed, but rather
than return

    (("Allows interactive calls." (interactive "^P"))
     nil)

I think it should return something like

    (("Allows interactive calls." (interactive "^P"))
     ,(macroexp-warn-and-return "Missing body" ...))
    

-- Stefan