Errors are unhelpful when variable type context disagrees with generic-involved dunder expression result

**Bug Report** In cases where a variable's type context (annotation) disagrees with the type of an expression involving a generic dunder, mypy produces very confusing/unhelpful errors. **To Reproduce** https://mypy-play.net/?mypy=latest&python=3.12&gist=0db2f883b65833b84089938fbcaa74d9 ```python class Parser[T]: def __init__(self, value: T) -> None: self.value: T = value def __or__[V](self, other: Parser[V]) -> Parser[T | V]: raise NotImplementedError def int_parser() -> Parser[int]: raise NotImplementedError def str_parser() -> Parser[str]: raise NotImplementedError # Expected: main.py:16: error: Incompatible types in assignment (expression has type "Parser[int | str]", variable has type "Parser[int]") [assignment] # Actual: main.py:16: error: Unsupported operand types for | ("Parser[int]" and "Parser[str]") [operator] issue1: Parser[int] = int_parser() | str_parser() # Expected: main.py:20: error: Incompatible types in assignment (expression has type "Parser[int | str]", variable has type "Parser[int]") [assignment] # Actual: main.py:20: error: Argument 1 to "Parser" has incompatible type "str"; expected "int" [arg-type] issue2: Parser[int] = Parser(1) | Parser("") # Correct: main.py:23: error: Incompatible types in assignment (expression has type "Parser[str]", variable has type "Parser[int]") [assignment] correct: Parser[int] = str_parser() ``` **Expected Behavior** All three assignment statements should give the `assignment` error, as it is much clearer on the issue in your code. **Actual Behavior** See above code snippet comments This error: `Unsupported operand types for | ("Parser[int]" and "Parser[str]") [operator]` Makes no sense, as `__or__` on `Parser` is defined in such a way that a `__or__` call is always valid This error: `Argument 1 to "Parser" has incompatible type "str"; expected "int" [arg-type]` Makes no sense, as the `Parser` `__init__` accepts any type as an input. It makes more sense in-type-context, but is still a much more confusing error than the expected `assignment` error. **Your Environment** Reproduced on online playground using both latest (2.1.0) and master.