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Use normalized tuples for fallback calculation #19111

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Merged
merged 6 commits into from
Jul 22, 2025
Merged

Use normalized tuples for fallback calculation #19111

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9b6f908
Normalize tuples before calculating the fallback
sterliakov May 19, 2025
3989212
Merge remote-tracking branch 'upstream/master' into bugfix/gh-19105-t…
sterliakov Jul 4, 2025
bebdf28
Maybe this?
sterliakov Jul 4, 2025
0aaa011
Fix selfcheck
sterliakov Jul 4, 2025
8bb25fa
And a test
sterliakov Jul 4, 2025
03a0a5b
Merge branch 'master' into bugfix/gh-19105-trivial-unpack-in-base-cla…
sterliakov Jul 21, 2025
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3 changes: 2 additions & 1 deletion mypy/semanal_shared.py
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@
TypeVarLikeType,
TypeVarTupleType,
UnpackType,
flatten_nested_tuples,
get_proper_type,
)

Expand Down Expand Up @@ -290,7 +291,7 @@ def calculate_tuple_fallback(typ: TupleType) -> None:
fallback = typ.partial_fallback
assert fallback.type.fullname == "builtins.tuple"
items = []
for item in typ.items:
for item in flatten_nested_tuples(typ.items):
# TODO: this duplicates some logic in typeops.tuple_fallback().
if isinstance(item, UnpackType):
unpacked_type = get_proper_type(item.type)
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8 changes: 8 additions & 0 deletions test-data/unit/check-typevar-tuple.test
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Expand Up @@ -2628,3 +2628,11 @@ def fn(f: Callable[[*tuple[T]], int]) -> Callable[[*tuple[T]], int]: ...
def test(*args: Unpack[tuple[T]]) -> int: ...
reveal_type(fn(test)) # N: Revealed type is "def [T] (T`1) -> builtins.int"
[builtins fixtures/tuple.pyi]

[case testNoCrashSubclassingTUpleWithTrivialUnpack]
# https://github.com/python/mypy/issues/19105
from typing import Unpack

class A(tuple[Unpack[tuple[int]]]): ...
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@ilevkivskyi ilevkivskyi May 19, 2025

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Could you please also add a test for

class C(tuple[Unpack[tuple[int, ...]]]): ...

(unless there is already such test case)? I am not sure we properly handle such types. Also maybe test not just class creation, but some tuple ops as well, such as e.g. unpacking etc.

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@sterliakov sterliakov May 19, 2025

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Surprisingly we don't have such a test too, but it was already working before my patch - *tuple[int, ...] is not a trivial unpack. But your feeling is overall correct - I'm able to make it crash with

a: A
tuple(a)

and also get a terrible diagnostic on

b: B
_, = b  # E: Variadic tuple unpacking requires a star target

despite B clearly not being variadic. I'll move this to draft for now, there's little benefit from merging a crash fix that causes a next one immediately...

class B(tuple[Unpack[tuple[()]]]): ...
[builtins fixtures/tuple.pyi]