Sema: Fix type resolution with invalid nested protocol

If you have a class with an (invalid) protocol nested inside:

    class OuterGenericClass<T, U> {
      protocol InnerProtocol : OuterGenericClass {}
    }

The reference to 'OuterGenericClass' in the protocol's inheritance
clause is not "in context", and should not have inferred generic
arguments <T, U>, because the protocol does not inherit the generic
arguments of the outer scope.

Previously, this would trigger an assertion in the requirement
machine, because the generic parameter τ_0_1 is not a valid generic
parameter in the protocol's generic signature.

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -401,7 +401,7 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
     // type within the context.
     if (auto *nominalType = dyn_cast<NominalTypeDecl>(typeDecl)) {
       for (auto *parentDC = fromDC; !parentDC->isModuleScopeContext();
-           parentDC = parentDC->getParent()) {
+           parentDC = parentDC->getParentForLookup()) {
         auto *parentNominal = parentDC->getSelfNominalTypeDecl();
         if (parentNominal == nominalType)
           return mapTypeIntoContext(parentDC->getDeclaredInterfaceType());
@@ -421,7 +421,7 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
     // referenced without generic arguments as well.
     if (auto *aliasDecl = dyn_cast<TypeAliasDecl>(typeDecl)) {
       for (auto *parentDC = fromDC; !parentDC->isModuleScopeContext();
-           parentDC = parentDC->getParent()) {
+           parentDC = parentDC->getParentForLookup()) {
         if (auto *ext = dyn_cast<ExtensionDecl>(parentDC)) {
           auto extendedType = ext->getExtendedType();
           if (auto *unboundGeneric =

test/decl/nested/protocol.swift

@@ -68,10 +68,14 @@ class OuterClass {
   // expected-error@-1{{protocol 'InnerProtocol' cannot be nested inside another declaration}}
 }
 
-class OtherGenericClass<T> {
+// 'InnerProtocol' does not inherit the generic parameters of
+// 'OtherGenericClass', so the occurrence of 'OtherGenericClass'
+// in 'InnerProtocol' is not "in context" with implicitly
+// inferred generic arguments <T, U>.
+class OtherGenericClass<T, U> { // expected-note {{generic type 'OtherGenericClass' declared here}}
   protocol InnerProtocol : OtherGenericClass { }
   // expected-error@-1{{protocol 'InnerProtocol' cannot be nested inside another declaration}}
-  // expected-error@-2{{superclass constraint 'Self' : 'OtherGenericClass<Self>' is recursive}}
+  // expected-error@-2{{reference to generic type 'OtherGenericClass' requires arguments in <...>}}
 }
 
 protocol SelfDotTest {