Generic typeddict may corrupt the cache

[Synss]

Bug Report

Using a generic TypedDict in another module may corrupt the cache. The cache doesn't recover and must be deleted.

To Reproduce

In module a, define a generic TypedDict,

# a.py
from typing import TypedDict, Generic, TypeVar

TValue = TypeVar("TValue")


class Dict(TypedDict, Generic[TValue]):
    value: TValue

in another module (say b) use this definition. The easiest way to trigger the bug is to have at least one typing error in the file (here g()).

# b.py
from a import Dict, TValue

def f(d: Dict[TValue]) -> TValue:
    return d["value"]


def g(d: Dict[TValue]) -> TValue:
    return d["x"]  # error

Now, type check b

$ mypy b.py
b.py:8: error: TypedDict "a.Dict[TValue]" has no key "x"  [typeddict-item]
Found 1 error in 1 file (checked 1 source file)

as expected.

However, running mypy b.py a second time reports an extra [type-arg] and a few more related errors as well,

$ mypy b.py
b.py:3: error: "Dict" expects no type arguments, but 1 given  [type-arg]
b.py:3: error: A function returning TypeVar should receive at least one argument containing the same TypeVar  [type-var]
b.py:4: error: Incompatible return value type (got "TValue", expected "TValue")  [return-value]
b.py:7: error: "Dict" expects no type arguments, but 1 given  [type-arg]
b.py:7: error: A function returning TypeVar should receive at least one argument containing the same TypeVar  [type-var]
b.py:8: error: TypedDict "a.Dict[TValue]" has no key "x"  [typeddict-item]
Found 6 errors in 1 file (checked 1 source file)

from then on, the only way to get rid of the [type-arg] error is to run with --no-increment or delete the cache. Here, I removed g(), leaving

# b.py [edited: deleted definition of g()]
from a import Dict, TValue

def f(d: Dict[TValue]) -> TValue:
    return d["value"]

and

$ mypy b.py
b.py:3: error: "Dict" expects no type arguments, but 1 given  [type-arg]
b.py:3: error: A function returning TypeVar should receive at least one argument containing the same TypeVar  [type-var]
b.py:4: error: Incompatible return value type (got "TValue", expected "TValue")  [return-value]
Found 3 errors in 1 file (checked 1 source file)

but

$ mypy --no-increment b.py
Success: no issues found in 1 source file

Expected Behavior

No difference between mypy, mypy --no-increment and the generic TypedDict do not corrupt the cache.

Actual Behavior

mypy reports false positives

b.py:3: error: "Dict" expects no type arguments, but 1 given  [type-arg]
b.py:3: error: A function returning TypeVar should receive at least one argument containing the same TypeVar  [type-var]
b.py:4: error: Incompatible return value type (got "TValue", expected "TValue")  [return-value]

Your Environment

• Mypy version used: 0.991, 1.0.0, master
• Mypy command-line flags: mypy vs. mypy --no-increment
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11 or importing TypedDict from mypy_extensions on Python 3.10.

I could also reproduce that under Linux (Ubuntu 22.04) and MacOS (M1---Python installed via MacPorts).