bug#69387: 30.0.50; A string shouldn't be both a docstring and a return value

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

>>> (defun (ARGS) "string") -> (defun (ARGS) "string" "string")
>>> to preserve semantics (and the same for defmacro, cl-defun, etc).
>> I still haven't seen any code that wants this behavior, so that's
>> a definite no for me.
> I presume you mean that `defun`s with a single string always want it to be
> their doc string? That indeed seems to be the dominant use. These are the
> few counter-examples that I could find:

No, I mean that we should not keep the old dual-use semantics, even if
it means some docstrings get temporarily "lost" until the code is fixed.

As for whether (defun (ARGS) "string") should treat the string as
a docstring or a return value, I'd rather keep it as a return value, so
it's the same as for `lambda`.  Another reason is because, the kind of
failures it is likely to introduce is a lot more mild: it's much safer
to remove a docstring than to change the return value.

So far, the harder part of such a change (beside getting it accepted 🙂)
seems to be the font-lock highlighting.


        Stefan