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Fix type inference for index expression with bounded TypeVar #11434

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Merged
JukkaL merged 3 commits into from
Nov 9, 2021
Merged

Fix type inference for index expression with bounded TypeVar #11434

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59db820
Fix type inference for index expression with bounded TypeVar
ilyalabun Nov 2, 2021
8dc3315
Add tests for TypeVar in Union and for TypeVar with values
ilyalabun Nov 3, 2021
d40b2b0
Corner case -- recursive TypeVar `T`
ilyalabun Nov 7, 2021
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3 changes: 3 additions & 0 deletions mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2960,6 +2960,9 @@ def visit_index_with_type(self, left_type: Type, e: IndexExpr,
elif (isinstance(left_type, CallableType)
and left_type.is_type_obj() and left_type.type_object().is_enum):
return self.visit_enum_index_expr(left_type.type_object(), e.index, e)
elif (isinstance(left_type, TypeVarType)
and not self.has_member(left_type.upper_bound, "__getitem__")):
return self.visit_index_with_type(left_type.upper_bound, e, original_type)

@sobolevn sobolevn Nov 3, 2021 •
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What if this type var has .values instead of .upper_bound? Will it still work?

@ilyalabun ilyalabun Nov 3, 2021 •
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surprisingly it works. I'm not sure why, but I suspect it's related to TypeVars expansion in checker.py::check_func_def. Added test for this case as well

else:
result, method_type = self.check_method_call_by_name(
'__getitem__', left_type, [e.index], [ARG_POS], e,
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71 changes: 71 additions & 0 deletions test-data/unit/check-typevar-values.test
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Expand Up @@ -631,3 +631,74 @@ def g(s: S) -> Callable[[S], None]: ...
def f(x: S) -> None:
h = g(x)
h(x)

[case testTypeVarWithTypedDictBoundInIndexExpression]
from typing import TypeVar
from typing_extensions import TypedDict

class Data(TypedDict):
x: int


T = TypeVar("T", bound=Data)

@sobolevn sobolevn Nov 3, 2021

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Will the same work for bound=Union[Data, Other]?

@ilyalabun ilyalabun Nov 3, 2021

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yes, it works because Union is handled in visit_index_with_type by processing Union items recursively. Added test for this case.



def f(data: T) -> None:
reveal_type(data["x"]) # N: Revealed type is "builtins.int"
[builtins fixtures/tuple.pyi]

[case testTypeVarWithUnionTypedDictBoundInIndexExpression]
from typing import TypeVar, Union, Dict
from typing_extensions import TypedDict

class Data(TypedDict):
x: int


T = TypeVar("T", bound=Union[Data, Dict[str, str]])


def f(data: T) -> None:
reveal_type(data["x"]) # N: Revealed type is "Union[builtins.int, builtins.str*]"

[builtins fixtures/tuple.pyi]
[builtins fixtures/dict.pyi]

[case testTypeVarWithTypedDictValueInIndexExpression]
from typing import TypeVar, Union, Dict
from typing_extensions import TypedDict

class Data(TypedDict):
x: int


T = TypeVar("T", Data, Dict[str, str])


def f(data: T) -> None:
_: Union[str, int] = data["x"]
[builtins fixtures/tuple.pyi]
[builtins fixtures/dict.pyi]

[case testSelfTypeVarIndexExpr]
from typing import TypeVar, Union, Type
from typing_extensions import TypedDict

T = TypeVar("T", bound="Indexable")

class Indexable:
def __init__(self, index: str) -> None:
self.index = index

def __getitem__(self: T, index: str) -> T:
return self._new_instance(index)

@classmethod
def _new_instance(cls: Type[T], index: str) -> T:
return cls("foo")

def m(self: T) -> T:
return self["foo"]

[builtins fixtures/tuple.pyi]
[builtins fixtures/classmethod.pyi]