In #30614, we started consuming XRefNonLoadedModuleErrors while loading
conformances, since a conformance to a type we cannot load usually
indicates we're trying to load a protocol that was declared in an
@_implementationOnly imported module.
We should also consume TypeErrors that we see where the underlying reason
is an XRefNonLoadedModuleError, since they're likely indicators of the
same thing.
We already ban all structs from declaring storage that comes from implementation-only imports. Until now we missed property wrappers, they were just dropped in deserialization.
Resolves rdar://problem/59403617
Components of a requirement may be hidden behind an implementation-only
import. Attempts at deserializing them would fail on a 'module not
loaded' error. We only see failures in non-compilation paths, either in
indexing or with tools like ide-test as they try to deserialize
things that are private.
Harden more of the serialization functions to propagate errors for
the caller to handle these errors gracefully. This fixes a crash in
finishNormalConformance when indexing a system module with an
implementation-only import.
rdar://problem/52837313
