False negative: `typing.Literal[<Union expression>]`

Bug Report, To Reproduce, & Actual Behaviour

See mypy playground

from typing import Literal

a: Literal[1 | None]
reveal_type(a)

note: Revealed type is "Union[Literal[1], None]"
Success: no issues found in 1 source file

For the runtime counterpart, this will result in a TypeError: unsupported operand type(s) for |: 'int' and 'NoneType' if the module doesn't have from __future__ import annotations or invalid results for runtime annotation inspectors (e.g. in the case of typing.Literal[1 | 2]).

Expected Behavior

Maybe:

error: Invalid type: Literal[...] cannot contain arbitrary expressions  [valid-type]
note: Revealed type is "Any"

Your Environment

• Mypy version used: 1.10
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10 & 3.12

Start by reproducing the example in the linked mypy playground with Python 3.10 or 3.12 and the shown Literal[1 | None] annotation. Trace how mypy handles Literal arguments and compare the result with the proposed invalid-type diagnostic and Any reveal; done means arbitrary union expressions are rejected consistently.