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Fix crash with function redefinition #14064

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merged 2 commits into from Nov 11, 2022
Merged

Fix crash with function redefinition #14064

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4c4cf8f
Fix crash with function redefinition
hauntsaninja Nov 11, 2022
c373999
code review
hauntsaninja Nov 11, 2022
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6 changes: 5 additions & 1 deletion mypy/checker.py
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Expand Up @@ -960,7 +960,11 @@ def _visit_func_def(self, defn: FuncDef) -> None:
# Function definition overrides a variable initialized via assignment or a
# decorated function.
orig_type = defn.original_def.type
assert orig_type is not None, f"Error checking function redefinition {defn}"
if orig_type is None:
# I'm not sure why this happens, probably a bug elsewhere
# See testConditionalFunctionDefinitionWithTuple
# Setting orig_type to UninhabitedType ensures an error is reported
orig_type = UninhabitedType()
if isinstance(orig_type, PartialType):
if orig_type.type is None:
# Ah this is a partial type. Give it the type of the function.
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11 changes: 11 additions & 0 deletions test-data/unit/check-functions.test
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Expand Up @@ -1475,6 +1475,17 @@ else:
@dec
def f(): pass

[case testConditionalFunctionDefinitionWithTuple]
def bar() -> None:
# weirdly, needs to be an empty tuple. empty lists and various other special assignments
# don't trigger the bug
cond = ()
if cond:
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A simpler test would be just if False: The problem is that mypy considers if branch unreachable, and therefore doesn't type check it, and therefore the original definition doesn't get its type inferred (and stays None).

I think a better solution is to simply not show any error in this case:

  • It will be more consistent with not showing error in unreachable code
  • Technically, there is no redefinition, only one definition is ever executed.

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Note however, this will be inconsistent with foo: int = 1, where user will get an error, even if the first definition is unreachable, but IMO this is OK.

foo = 1
else:
def foo(obj): ... # E: Incompatible redefinition (redefinition with type "Callable[[Any], Any]", original type <nothing>)
[builtins fixtures/tuple.pyi]

[case testConditionalRedefinitionOfAnUnconditionalFunctionDefinition1]
from typing import Any
def f(x: str) -> None: pass
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