Literal pattern matching

[miroslavbel]

I hope I haven't made a mistake by asking here instead of in the mypy repository.

Is there a rationale for the discrepancy in the types in this two cases? In the first case (if_stmt), reveal_type correctly identifies the types, while in the second case (match_stmt), None seemingly appears out of nowhere. As I understand, is the issue related to type narrowing?

Code

gist, mypy-playground

from typing import Literal, TypedDict, Union, reveal_type


IntArrayElements = TypedDict("IntArrayElements", {"elements": list[int]})

IntArrayStruct = TypedDict(
    "IntArrayStruct",
    {"data": IntArrayElements, "type": Literal["INT_ARRAY"]},
)
NoneStruct = TypedDict(
    "NoneStruct",
    {"data": None, "type": Literal["NONE"]},
)


response: list[Union[IntArrayStruct, NoneStruct]] = []



for item in response:
    if item['type'] == 'INT_ARRAY':
        _0_data = item["data"]
        reveal_type(_0_data)

        _0_elements = _0_data['elements']
        reveal_type(_0_elements)

    else:
        pass

for item in response:
    match item['type']:
        case 'INT_ARRAY':
            _1_data = item["data"]
            reveal_type(_1_data)         # Line:35

            _1_elements = _1_data['elements']
            reveal_type(_1_elements)     # Line:38

        case _:
            pass

Expected Behavior

...
main.py:35: note: Revealed type is "TypedDict('__main__.IntArrayElements', {'elements': builtins.list[builtins.int]})"
main.py:38: note: Revealed type is "builtins.list[builtins.int]"
...

Actual Behavior

...
main.py:35: note: Revealed type is "Union[TypedDict('__main__.IntArrayElements', {'elements': builtins.list[builtins.int]}), None]"
...
main.py:38: note: Revealed type is "Union[builtins.list[builtins.int], Any]"
...

[hauntsaninja]

My guess is mypy is missing the tagged union code when handling match statements

[tmke8]

See #15190 and #16286

[hauntsaninja]

Closing as duplicate of #16286