Summary

Fixes #11835

Since #9102 (1.1.383), specializing a generic type alias infers its variance. When a property getter's return annotation specializes an alias that refers back to a class with inferred variance, pyright reports the setter's decorator as an unknown attribute of a function and the getter as obscured.

Root cause

Inferring the class's variance evaluates the declared type of each member. For a property, that is the setter, whose decorator refers to the getter while the getter is still being decorated, so the decorator's base type is an incomplete function.

• getTypeOfMemberAccessWithBaseType looks up an attribute of a function on the function or MethodType class, but passes that lookup a base type without isIncomplete, so it reports the missing attribute.
• getTypeOfFunction caches the decorated type as final even when a decorator's type was incomplete. The setter's decorated type stays Any after the getter is complete, and the redeclaration check reports the getter as obscured.

Fix

The function member lookup keeps the base type's incompleteness, and a decorated type built from an incomplete decorator is cached as incomplete, so it is evaluated again once the getter is complete.

Test

diagnostics.propertySetterVarianceInference.fourslash.ts, a fourslash test because the sample-file harness evaluates the getter before the checker reaches the annotation:

• test1.py: a getter and setter whose return annotation specializes an alias referring to the class. Must stay clean.
• test2.py: the same with a misspelled setter attribute. Must still flag it as an unknown attribute of property, and the getter as obscured.