GNU bug report logs -
#58601
29.0.50; Infinite loop in byte-compile--first-symbol-with-pos
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Reported by: "Basil L. Contovounesios" <contovob <at> tcd.ie>
Date: Mon, 17 Oct 2022 23:25:01 UTC
Severity: normal
Found in version 29.0.50
Done: Stefan Monnier <monnier <at> iro.umontreal.ca>
Bug is archived. No further changes may be made.
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Message #40 received at 58601 <at> debbugs.gnu.org (full text, mbox):
>> 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.
Circular data is not very frequent, but it's not rare either (as you
found out during the development of sympos, as evidenced by
`byte-run--ssp-seen`).
`byte-compile--first-symbol-with-pos` didn't bump into it until now
simply because it usually gets "lucky" and finds a sympos before getting
to a cyclic embedded data.
> Have you ever seen anything at all like this in real life?
Of course, and so have you :-)
> You have fixed this "problem" by arbitrarily limiting the size of
> valid form stacks that can be searched, and the depth to which they
> can be searched. This limit, 10, seems too small. There can easily
> be form stacks with more than 10 elements. Do you have any objection
> if I change that 10 to something closer to infinity?
Be my guest.
> Something which will encompass any form stack likely to be
> encountered in practice? I would suggest the number 300.
Fine by me. Tho once we get into this range, 666 sounds a lot
more enticing. :-)
Stefan
This bug report was last modified 2 years and 300 days ago.
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