erroneous type mismatch with `Union` and `Literal` (false positive)

Bug Report

Mypy does not sufficiently simplify Unions and Literals before some type checks (the reproduction case uses assert_type(), but assignments and calls will also trigger the issue). The result is false positive errors.

To Reproduce

[mypy-play.net]

from __future__ import annotations
from enum import (
        Enum,
        auto,
        )
from typing import (
        Literal,
        Union,
        )
from typing_extensions import (
        assert_type,
        reveal_type,
        )

class Color(Enum):
    RED = auto()
    GREEN = auto()
    BLUE = auto()

RedKwds = Literal['RED', 'R']
GreenKwds = Literal['GREEN', 'G']
BlueKwds = Literal['BLUE', 'B']
ColorKwds = Union[RedKwds, GreenKwds, BlueKwds]

RedSpec = Union[Literal[Color.RED], RedKwds]
GreenSpec = Union[Literal[Color.GREEN], GreenKwds]
BlueSpec = Union[Literal[Color.BLUE], BlueKwds]

ColorSpec = Union[Color, ColorKwds]             # ⎱ these are entirely
RGBSpec = Union[RedSpec, GreenSpec, BlueSpec]   # ⎰ equivalent types


rgb_spec: RGBSpec
assert_type(rgb_spec, ColorSpec)  # fails; should be silent             # L34
        # Expression is of type...
        #   Union[
        #       Union[Literal[Color.RED], Literal['RED', 'R']],
        #       Union[Literal[Color.GREEN], Literal['GREEN', 'G']],
        #       Union[Literal[Color.BLUE], Literal['BLUE', 'B']]
        #       ]
        # ... not ...
        #   Union[
        #       Color,
        #       Union[
        #           Literal['RED', 'R'],
        #           Literal['GREEN', 'G'],
        #           Literal['BLUE', 'B']
        #           ]
        #       ]
reveal_type(rgb_spec)                                                   # L50
        # Union[
        #       Literal[Color.RED], Literal['RED'], Literal['R'],
        #       Literal[Color.GREEN], Literal['GREEN'], Literal['G'],
        #       Literal[Color.BLUE], Literal['BLUE'], Literal['B']
        #       ]


# "shaking" the variable (where "shaking" is clearly a no-op) causes
# things to work as expected:
rgb_spec_shaken = (
        rgb_spec
        if isinstance(rgb_spec, Color) else
        rgb_spec
        )
assert_type(rgb_spec_shaken, ColorSpec)  # passes!
reveal_type(rgb_spec_shaken)                                            # L66
        # Union[
        #       Color,
        #       Literal['RED'], Literal['R'],
        #       Literal['GREEN'], Literal['G'],
        #       Literal['BLUE'], Literal['B']
        #       ]

Expected Behavior

The types are provably equivalent; no error should be raised.

Actual Behavior

Mypy does not sufficiently simplify the types, resulting in an erroneous "mismatch".

Your Environment

• Mypy version used: 1.9.0, master 2024-04-22
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8, 3.12

Commencez par exécuter la reproduction mypy-play de l'issue avec les cas assert_type() et reveal_type() présentés, en particulier les lignes 34 et 50, puis examinez les chemins de simplification et de compatibilité des types impliqués dans ces vérifications. Le travail est terminé lorsque des types Union et Literal équivalents ne produisent plus de discordance et que le type révélé affiché est correctement simplifié.