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Fix Incompatible return value type error message for long tuple with Union and non-Union type mismatch #18881

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Merged
merged 6 commits into from
Apr 6, 2025
Merged

Fix Incompatible return value type error message for long tuple with Union and non-Union type mismatch #18881

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a58a971
fix: check for type strict equality to include union and non-union mi…
Luunynliny Apr 2, 2025
220a2f4
test: union and non-union type mismatch case
Luunynliny Apr 4, 2025
11a6c13
refactor: tuple types subtype check
Luunynliny Apr 4, 2025
9109962
test: wider expected return value
Luunynliny Apr 4, 2025
57177bf
test: better case names
Luunynliny Apr 4, 2025
e36a0c7
refactor: move test
Luunynliny Apr 5, 2025
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6 changes: 5 additions & 1 deletion mypy/messages.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2439,7 +2439,11 @@ def generate_incompatible_tuple_error(
error_cnt = 0
notes: list[str] = []
for i, (lhs_t, rhs_t) in enumerate(zip(lhs_types, rhs_types)):
if not is_subtype(lhs_t, rhs_t):
# If `lhs_t` is a subtype of `rhs_t`, ensure it's not strictly equal
# to capture both union and non-union mismatches.
# Example: is_subtype(str, str | None) -> True, but this should still be an error
# as is_same_type(str, str | None) -> False
if not is_subtype(lhs_t, rhs_t) or not is_same_type(lhs_t, rhs_t):
if error_cnt < 3:
notes.append(
"Expression tuple item {} has type {}; {} expected; ".format(
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39 changes: 39 additions & 0 deletions test-data/unit/check-classes.test
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Expand Up @@ -1665,6 +1665,45 @@ a.f = a.f # E: Property "f" defined in "A" is read-only
a.f.x # E: "int" has no attribute "x"
[builtins fixtures/property.pyi]

[case testPropertyWithTupleUnionAndNonUnionMismatchReturnValueType]
from typing import Tuple, Union
class A:
a: str
b: str
c: str
d: str
e: str
f: str
g: Union[str, int]
h: Union[str, float]
i: Union[str, None]
j: Union[str, None]
k: Union[str, None]
l: Union[str, None]

@property
def x(self) -> Tuple[str, str, str, str, str, str, str, str, str, str, str, str]:
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@sterliakov sterliakov Apr 4, 2025

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Please add a testcase with the opposite direction (annotated with tuple of unions, returns tuple of props)

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@Luunynliny Luunynliny Apr 4, 2025 •
edited
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@sterliakov Just to make sure I understand, you would like me to test this configuration ?
Or something else ?

class A:
    a: str
    b: str
    c: str
    d: str
    e: str
    f: str
    g: str
    h: str
    i: str
    j: str
    k: str
    l: str

    @property
    def x(self) -> Tuple[Union[str, int], Union[str, float], Union[str, None], Union[str, None], Union[str, None], Union[str, None], str, str, str, str, str, str]:
        return (
            self.a,
            self.b,
            self.c,
            self.d,
            self.e,
            self.f,
            self.g,
            self.h,
            self.i,
            self.j,
            self.k,
            self.l,
        )

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@sterliakov sterliakov Apr 4, 2025 •
edited
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I'd love to see a test where the expected return type is wider than the actual return type, but the changed method is still triggered. In your example all items are assignable, so that method won't fire. Something like

class A:
    a: str
    b: str
    c: str
    d: str
    e: str
    f: str
    g: str
    h: str
    i: str
    j: str
    k: str
    l: str

    @property
    def x(self) -> Tuple[Union[str, int], Union[str, float], int, Union[str, None], Union[str, None], Union[str, None], str, str, str, str, str, str]:
        return (
            self.a,
            self.b,
            self.c,
            self.d,
            self.e,
            self.f,
            self.g,
            self.h,
            self.i,
            self.j,
            self.k,
            self.l,
        )

I adjusted the third union item to not be assignable, so that the comparator should be triggered (please check that it actually is). And why is x a property, won't a simpler test without class do (and same question about the test you already added)?

a: str
b: str
c: str
d: str
e: str
f: str
g: str
h: str
i: str
j: str
k: str
l: str

x: Tuple[
    Union[str, int], Union[str, float], int, Union[str, None], Union[str, None],
    Union[str, None], str, str, str, str, 
    str, str,
] = (
    a, b, c, d, e,
    f, g, h, i, j,
    k, l,
)

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@sterliakov sterliakov Apr 4, 2025

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And a nit: please move this to check-tuples.test as the long tuple is the problem here, not the surrounding class.

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@Luunynliny Luunynliny Apr 4, 2025 •
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Thanks for the clarification and the provided example.

I adjusted the third union item to not be assignable, so that the comparator should be triggered (please check that it actually is).

It indeed triggers to relevant error. I also a Union to modified code works as expected.

And why is x a property, won't a simpler test without class do (and same question about the test you already added)?

Beside beging the configuration where I first encountered the error message issue, your suggestion triggers an Incompatible types in assignment (which works correctly) instead of a Incompatible return value type.

return (
self.a,
self.b,
self.c,
self.d,
self.e,
self.f,
self.g,
self.h,
self.i,
self.j,
self.k,
self.l,
)
[out]
main:18: error: Incompatible return value type (6 tuple items are incompatible; 3 items are omitted)
main:18: note: Expression tuple item 6 has type "Union[str, int]"; "str" expected;
main:18: note: Expression tuple item 7 has type "Union[str, float]"; "str" expected;
main:18: note: Expression tuple item 8 has type "Optional[str]"; "str" expected;
[builtins fixtures/property.pyi]

-- Descriptors
-- -----------

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