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dmypy suggest crashes on __new__ with IndexError #18964

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asottile-sentry opened this issue Apr 24, 2025 · 0 comments · May be fixed by #18966
Open

dmypy suggest crashes on __new__ with IndexError #18964

asottile-sentry opened this issue Apr 24, 2025 · 0 comments · May be fixed by #18966
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crash topic-daemon dmypy

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@asottile-sentry
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Bug Report

a crash occurs when requesting suggestions for __new__ with no args and a caller

just a guess at the line since I haven't poked it yet -- I think the problem is here:

mypy/mypy/suggestions.py

Line 350 in 1ea9373

for typ in call.arg_types[i - is_method]:
(and that __new__ is not considered is_method = True)

To Reproduce

class C:
    def __new__(cls):
        return cls()

c = C()

Expected Behavior

probably () -> C or () -> Self ?

Actual Behavior

$ dmypy run t.py
Daemon started
Success: no issues found in 1 source file
$ dmypy suggest t.C.__new__
Daemon crashed!
Traceback (most recent call last):
  File "mypy/dmypy_server.py", line 237, in serve
  File "mypy/dmypy_server.py", line 286, in run_command
  File "mypy/dmypy_server.py", line 983, in cmd_suggest
  File "mypy/suggestions.py", line 267, in suggest
  File "mypy/suggestions.py", line 480, in get_suggestion
  File "mypy/suggestions.py", line 404, in get_guesses
  File "mypy/suggestions.py", line 350, in get_args
IndexError: list index out of range

Your Environment

  • Mypy version used: 1.15.0
  • Mypy command-line flags: see above
  • Mypy configuration options from mypy.ini (and other config files): n/a
  • Python version used: 3.13.1
@asottile-sentry asottile-sentry added the bug mypy got something wrong label Apr 24, 2025
@sterliakov sterliakov added crash topic-daemon dmypy and removed bug mypy got something wrong labels Apr 24, 2025
@asottile-sentry asottile-sentry mentioned this issue Apr 24, 2025
Merged
asottile-sentry added a commit to getsentry/sentry that referenced this issue Apr 24, 2025
@asottile-sentry
ref: use a more typing-friendly singleton for backup ScrubbedData (#9…
32e83e3 
…0297)

avoids this crash in mypy: python/mypy#18964

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@sterliakov sterliakov linked a pull request Apr 25, 2025 that will close this issue
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Fix dmypy suggest interaction with __new__ sterliakov/mypy
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@sterliakov @asottile-sentry