Sema: handle ~<<error type>> gracefully

Author: kavon

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -113,7 +113,7 @@ class CheckRepressions {
   /// repressed or return the inverted type.
   Type add(Type ty, InverseTypeRepr &repr,
            llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl) {
-    if (!ty)
+    if (!ty || ty->hasError())
       return Type();
     assert(!ty->is<ExistentialMetatypeType>());
     auto kp = ty->getKnownProtocol();

test/Parse/inverses.swift

@@ -4,6 +4,8 @@ protocol U {}
 
 enum Maybe<Thing: ~Copyable> : ~Copyable {}
 
+struct Pluto: ~Planet {} // expected-error {{cannot find type 'Planet' in scope}}
+
 func more() {
   let _: any ~Copyable = 19