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PEP 709: Crash with lambda + nested scope #104602

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JelleZijlstra opened this issue May 18, 2023 · 1 comment · Fixed by #104603
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PEP 709: Crash with lambda + nested scope #104602

JelleZijlstra opened this issue May 18, 2023 · 1 comment · Fixed by #104603
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@carljm
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type-bug An unexpected behavior, bug, or error

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@JelleZijlstra
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JelleZijlstra commented May 18, 2023 •
edited by bedevere-bot

This crashes on main:

def a():
    def a():
        [(lambda : b) for b in [a]]
        print(b)

The original reproducer (found with my fork of https://github.com/carljm/compgenerator) was

class a:
    def a():
        class a:
            [(lambda : (a := a[(a := 2)])[b]) for b in (lambda b, a: 7)[a]]
            [][2] = b
            (1)[lambda a: a] = 4
            (2)[2] = b = a
        (4)[lambda b, a: b] = a = lambda : 1

Found in #104528 (comment) but turned out be unrelated to that PR.

Linked PRs
@JelleZijlstra JelleZijlstra added the type-bug An unexpected behavior, bug, or error label May 18, 2023
carljm added a commit to carljm/cpython that referenced this issue May 18, 2023
@carljm
pythongh-104602: ensure all cellvars are known up front
c1442c5
@bedevere-bot bedevere-bot mentioned this issue May 18, 2023
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@JelleZijlstra JelleZijlstra mentioned this issue May 18, 2023
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@carljm carljm mentioned this issue May 18, 2023
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@carljm carljm linked a pull request May 18, 2023 that will close this issue
gh-104602: ensure all cellvars are known up front #104603
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carljm added a commit that referenced this issue May 19, 2023
@carljm @JelleZijlstra
gh-104602: ensure all cellvars are known up front (#104603)
86e6f16 
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
@JelleZijlstra
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Further fuzzing found this case that was also fixed by #104603:

class __a:
    __a[1] = [(1) for __b in [] for __a in [lambda : __a]]

This one failed as follows:

>>> class __a:
...     __a[1] = [(1) for __b in [] for __a in [lambda : __a]]
... 
SystemError: compiler_lookup_arg(name='_a__a') with reftype=5 failed in __a; freevars of code <lambda>: ('_a__a',)

which is different from the original repro case, which segfaulted. I'll see if I can distill a useful test case out of it.

JelleZijlstra added a commit to JelleZijlstra/cpython that referenced this issue May 19, 2023
@JelleZijlstra
pythongh-104602: Add additional test for listcomp with lambda
e3fa00f 
This threw a SystemError before python#104603. Adding a separate test
because this was a different failure mode than the other two new
tests from python#104603, both of which used to segfault.
@bedevere-bot bedevere-bot mentioned this issue May 19, 2023
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gh-104602: ensure all cellvars are known up front carljm/cpython
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