List constant expression treated differently to list literal

Bug Report

When assigning a list literal to a variable with a known type, mypy uses that type in inferring the type of the list literal. This gives the appearance that invariance is relaxed e.g.

x: list[int | None] = [0, 1, 2, 10]  # ok

is accepted even though normally a list[int] cannot be assigned to a list[int | None].

However, when the list literal is written as a more complex expression, that stops working:

x: list[int | None] = [0, 1, 2] + [10]  # error

That's obviously a bit contrived. My actual use case is more similar to this:

x: list[int | None] = [i for i in range(3)] + [10]  # error

Maybe this isn't fixable - it's only sound because list.__add__ returns a new list which has no other references, but I don't think there is a way to represent that in typeshed.

To Reproduce

x: list[int | None] = [0, 1, 2] + [10]

Expected Behavior

No error

Actual Behavior

concat2.py:1: error: Incompatible types in assignment (expression has type "list[int]", variable has type "list[int | None]")  [assignment]
concat2.py:1: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
concat2.py:1: note: Consider using "Sequence" instead, which is covariant

Your Environment

• Mypy version used: 2.2.0
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.12.3

En el issue no se indica ningún archivo de implementación ni ninguna prueba. Empieza reproduciendo la asignación indicada con mypy y, después, sigue cómo se infieren los literales de lista, la concatenación de listas y las comprensiones, y cómo se comprueban contra la variable anotada. Se considera terminado cuando los casos de concatenación indicados pasan sin debilitar las comprobaciones habituales de invariancia de las listas.