bug#41988: 28.0.50; Edebug unconditionally instruments definitions with &define specs

[Philipp]

> Am 05.04.2021 um 16:32 schrieb Philipp Stephani <p.stephani2@gmail.com>:
> 
>>>>> so I think it would be reasonable to prevent.  We already
>>>>> disable backtracking for literal symbols, and I think forms that require
>>>>> multiple &define forms with backtracking should be exceedingly rare and 
>>>>> can
>>>>> be rewritten as you did with cl-flet.
>>>> Emitting a warning would be much more helpful than just silently
>>>> "cut"ting the backtracking.
>>> A gate isn't silent, it would cause a hard error in this case.
>> 
>> What I meant is that a gate would just make the old cl-flet spec fail in
>> most cases, with no explanation why that spec now fails even though it
>> worked in the past.
> 
> Yes, we'd need to at least announce the change in NEWS as an
> incompatible Lisp change. However, I think overall that's still better
> than the current situation: with your fix to cl-flet the problematic
> constructs shouldn't occur any more in the Emacs codebase, and I
> wouldn't expect such constructs to be very frequent "in the wild", so
> the overall breakage would be very small, and if it can avoid
> similarly subtle bugs then I think it's warranted.

Here's a patch.

0001-Edebug-Disable-backtracking-when-hitting-a-define-ke.patch
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