Description

When func.coalesce is used with a hybrid property, the return type inferred is wrong. This can lead to suprising mypy errors, such as this:

class Foo(Base):
    __tablename__ = "foo"

    _bar: Mapped[int | None] = mapped_column("bar")
    
    @hybrid_property
    def bar(self) -> int | None:
        return self._bar
    
    @bar.inplace.expression
    @classmethod
    def _bar_expression(cls) -> ColumnElement[int]:
        return func.coalesce(cls._bar, 42)

Mypy output:

error: Argument 1 to "coalesce" of "_FunctionGenerator" has incompatible type "InstrumentedAttribute[int | None]"; expected "ColumnElement[int] | _HasClauseElement[int] | SQLCoreOperations[int] | ExpressionElementRole[int] | TypedColumnsClauseRole[int] | Callable[[], ColumnElement[int]] | LambdaElement"  [arg-type]

This PR aims to fix this issue.

Checklist

This pull request is:

• A documentation / typographical / small typing error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • please include the issue number, and create an issue if none exists, which
    must include a complete example of the issue. one line code fixes without an
    issue and demonstration will not be accepted.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests. one line code fixes without tests will not be accepted.
• A new feature implementation
  • please include the issue number, and create an issue if none exists, which must
    include a complete example of how the feature would look.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests.

Have a nice day!