Subject: Re: bug#58601: 29.0.50; Infinite loop in byte-compile--first-symbol-with-pos

From: "Basil L. Contovounesios" <[email-masked]>
Date: Fri, 21 Oct 2022 13:47:53 +0300

Alan Mackenzie [2022-10-19 08:52 +0000] wrote:

> On Tue, Oct 18, 2022 at 15:19:35 -0400, Stefan Monnier wrote:
>> >> That's not the problem, because it's just for illustrative purposes.
>> >> Instead of 'arg' being passed unchanged as the FORM argument, it could
>> >> just as well have been `(my-frobnicate ,arg).
>
>> > That would not loop, since there is a symbol with position there.
>
>> BTE, the real-world use case is a compiler macro which takes the list of
>> args and tucks the name of another function in front.  So the generated
>> code, passed to `macroexp-warn-and-return` has the shape
>
>>     (somefun somearg1 somearg2)
>
>> where `somefun` does *not* come from the source but from the
>> compiler-macro instead and hence doesn't have any sympos, and then
>> `somearg1` was an expression of the form
>
>>    (quote #1=(1 2 3 . #1#))
>
>> So, there was no cycle in the code part, the cycle is only inside the
>> data embedded in the code.
>
> I think somebody who writes something like that _deserves_ to go into an
> infinite loop.  Have you ever seen anything at all like this in real
> life?

See some of the recent commits listed in my other message.

-- 
Basil