Requirement lowering only expects that it won't see two requirements
of the same kind (except for conformance requirements). So only mark
those as conflicting.
This addresses a crash-on-invalid and improves diagnostics for
move-only generics, because a conflict won't drop the copyability
of a generic parameter and expose a move-only-naive user to
confusing error messages.
Fixes#61031.
Fixes#63997.
Fixes rdar://problem/111991454.
Use the FullyQualified<Type> abstraction from the prior commit plus DescriptiveDeclKind to give a bit more information when issuing a missing member type diagnostic during type resolution.
Name lookup might find an associated type whose protocol is not in our
conforms-to list, if we have a superclass constraint and the superclass
conforms to the associated type's protocol.
We used to return an unresolved type in this case, which would result in
the constraint getting delayed forever and dropped.
While playing wack-a-mole with regressing crashers, I had to do some
refactoring to get all the tests to pass. Unfortuanately these refactorings
don't lend themselves well to being peeled off into their own commits:
- maybeAddSameTypeRequirementForNestedType() was almost identical to
concretizeNestedTypeFromConcreteParent(), except for superclasses
instead of concrete same-type constraints. I merged them together.
- We used to drop same-type constraints where the subject type was an
ErrorType, because maybeResolveEquivalenceClass() would return an
unresolved type in this case.
This violated some invariants around nested types of ArchetypeTypes,
because now it was possible for a nested type of a concrete type to
be non-concrete, if the type witness in the conformance was missing
due to an error.
Fix this by removing the ErrorType hack, and adjusting a couple of
other places to handle ErrorTypes in order to avoid regressing with
invalid code.
Fixes <rdar://problem/45216921>, <https://bugs.swift.org/browse/SR-8945>,
<https://bugs.swift.org/browse/SR-12744>.
We need to make sure they don't end up as "concrete" equivalence
classes, because they behave more like unresolved ones.
Fixes rdar://problem/40009245.
