For now, hide `override fn`s from name lookup, so that the base class
version is always used, as the derived-class version does not have its
own vptr entry and so would not do the right thing if a further-derived
class adds a new override. This is implemented via a new access kind of
`Hidden`.
When checking the overriding function, pass in the expected `Self` type
and check the `self` parameter against that; the signature that we
generate for the thunk in the derived class is the base class signature
with the `self` parameter's type changed to the derived class.
When we generate a thunk for a virtual function, the thunk is assigned a
`virtual_index`, and the virtual function itself is not. When the thunk
makes a direct call to the virtual function, recognize this situation by
checking for a `virtual_index`, and perform a non-virtual call if there
isn't one.
Assisted-by: Gemini via Antigravity
When an outer type defines an `extend` relationship to an inner type, we
require that inner type to be complete so that we can know that name
lookup can search both scopes as soon as the outer type is complete.
When doing name lookup, we require the type in which we are looking to
be complete. Then, we recursively add extended scopes, but then also
require each of them to be complete again, which inserts
RequireCompleteType instructions into the block doing lookup.
While these new instructions may differ in terms of their specifics,
they are redundant since we already required the type to be complete,
and specifics can not change the completeness of a type. They are also
problematic because a named constraint or interface can extend a scope
with a symbolic specific, by using `Self` as an argument. This inserts a
symbolic instruction into the block doing name lookup, even though that
block may not be generic.
Richard Smith
Dana Jansens