Mypy should raise error on `Type[T]` where `T` is not valid

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers

Research direction

No file or test is named. Start by reproducing the reported Type[Optional[int]] case and locating the Type[...] validation in mypy; then inspect nearby type-checking tests. Done means invalid Type parameters produce an error while proper classes and unions remain accepted.

Written by the indexing model from the issue text.

Description

bug priority-1-normal topic-pep-484

As specified by PEP 484 (at least according to @ilevkivskyi), the only valid parameters for Type[] are proper classes and unions of proper classes.

Something like Type[Optional[int]] should raise an error.

Dominant language
Python
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Avg merge
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Merged PRs (30d)
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