variance okay for literals, but not expressions ([1, 2] okay for list[int | None] but [1] + [2] is error)

a: list[int | None] = [1] + [2] + [None]
b: list[int | None] = [1] + [2]
c: list[int | None] = [1, 2]

a is okay, b is an error, c is okay

Apologies if this is a repeat / common issue. I couldn't find anything in the docs. This is popping up for me a lot, my interpretation is that mypy allows type invariance on literals that it will not for expressions.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.11&gist=b999a1bd2e975645b868c0b376c910e8

Expected Behavior

Either b and c should both be errors or (preferably) neither.

Actual Behavior

b is an error but c isn't

Your Environment

• Mypy version used: 1.7.1 and master
• Python version used: 3.11

Beginne damit, die verlinkte mypy-play-Reproduktion mit mypy 1.7.1 oder master und Python 3.11 auszuführen, und vergleiche die Diagnosen für die Zuweisungen a, b und c. Fertig ist die Aufgabe, wenn sich das Verhalten für [1] + [2] gemäß dem im Issue angegebenen erwarteten Verhalten mit dem Verhalten für [1, 2] deckt.