10000 Fix `[func-returns-value]` not being trigged when calling decorated functions by brianschubert · Pull Request #18015 · python/mypy · GitHub
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Fix [func-returns-value] not being trigged when calling decorated functions #18015

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Fix [func-returns-value] not being trigged when calling decorated functions #18015

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ab766cc
Fix detection of decorated function always returning None
brianschubert Sep 26, 2024
db07091
Add test case for decorated functions that always return none
brianschubert Oct 22, 2024
21d8078
Fix handling of decorators that modify the function signature
brianschubert Oct 22, 2024
5cc0f23
Update test with changed behavior
brianschubert Oct 22, 2024
fe52ee1
Preserve original behavior for testLambdaReturningNone
brianschubert Oct 22, 2024
bdde260
Merge branch 'master' into gh-14179-decorated-func-returns-value
brianschubert Jul 13, 2025
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Fix handling of decorators that modify the function signature
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@brianschubert
brianschubert committed Oct 22, 2024
commit 21d8078c7fb1baf6f7fa6667c19c783ec577605e
8 changes: 3 additions & 5 deletions mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -717,7 +717,7 @@ def always_returns_none(self, node: Expression) -> bool:
def defn_returns_none(self, defn: SymbolNode | None) -> bool:
"""Check if `defn` can _only_ return None."""
if isinstance(defn, Decorator):
defn = defn.func
defn = defn.var
if isinstance(defn, FuncDef):
return isinstance(defn.type, CallableType) and isinstance(
get_proper_type(defn.type.ret_type), NoneType
Expand All @@ -726,10 +726,8 @@ def defn_returns_none(self, defn: SymbolNode | None) -> bool:
return all(self.defn_returns_none(item) for item in defn.items)
if isinstance(defn, Var):
typ = get_proper_type(defn.type)
if (
not defn.is_inferred
and isinstance(typ, CallableType)
and isinstance(get_proper_type(typ.ret_type), NoneType)
if isinstance(typ, CallableType) and isinstance(
get_proper_type(typ.ret_type), NoneType
):
return True
if isinstance(typ, Instance):
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24 changes: 22 additions & 2 deletions test-data/unit/check-expressions.test
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Original file line numberDiff line number Diff line change
Expand Up @@ -1152,9 +1152,25 @@ F = TypeVar('F', bound=Callable[..., Any])
def deco(f: F) -> F:
pass

def deco_return_none(f: object) -> Callable[..., None]:
pass

def deco_return_not_none(f: object) -> Callable[..., int]:
pass

@deco
@deco
def f() -> None:
def f1() -> None:
pass

@deco
@deco_return_none
def f2() -> int:
pass

@deco
@deco_return_not_none
def f3() -> None:
pass

class A:
Expand All @@ -1163,7 +1179,11 @@ class A:
pass

if int():
x = f() # E: "f" does not return a value (it only ever returns None)
x = f1() # E: "f1" does not return a value (it only ever returns None)
if int():
x = f2() # E: "f2" does not return a value (it only ever returns None)
if int():
x = f3()
if int():
x = A.s() # E: "s" of "A" does not return a value (it only ever returns None)
if int():
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