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

From: Stefan Monnier <[email-masked]>
Date: Tue, 18 Oct 2022 15:19:35 -0400

>> 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.

        Stefan