TypeCheckType: Do not form protocol type with generic parent in resolveTypeInContext

Author: AnthonyLatsis

include/swift/AST/DeclContext.h

@@ -586,6 +586,10 @@ class alignas(1 << DeclContextAlignInBits) DeclContext
   /// context.
   bool isInSpecializeExtensionContext() const;
 
+  /// Returns whether this declaration context is a protocol in an unsupported
+  /// context.
+  bool isUnsupportedNestedProtocol() const;
+
   /// Get the most optimal resilience expansion for code in this context.
   /// If the body is able to be inlined into functions in other resilience
   /// domains, this ensures that only sufficiently-conservative access patterns

lib/AST/Decl.cpp

@@ -5162,10 +5162,8 @@ static Type computeNominalType(NominalTypeDecl *decl, DeclTypeKind kind) {
   // If `decl` is a nested type, find the parent type.
   Type ParentTy;
   DeclContext *dc = decl->getDeclContext();
-  bool isUnsupportedNestedProtocol =
-    isa<ProtocolDecl>(decl) && decl->getParent()->isGenericContext();
 
-  if (!isUnsupportedNestedProtocol && dc->isTypeContext()) {
+  if (!decl->isUnsupportedNestedProtocol() && dc->isTypeContext()) {
     switch (kind) {
     case DeclTypeKind::DeclaredType: {
       if (auto *nominal = dc->getSelfNominalTypeDecl())

lib/AST/DeclContext.cpp

@@ -306,7 +306,7 @@ DeclContext *DeclContext::getParentForLookup() const {
     // outer types.
     return getModuleScopeContext();
   }
-  if (isa<ProtocolDecl>(this) && getParent()->isGenericContext()) {
+  if (isUnsupportedNestedProtocol()) {
     // Protocols in generic contexts must not look in to their parents,
     // as the parents may contain types with inferred implicit
     // generic parameters not present in the protocol's generic signature.
@@ -1532,6 +1532,10 @@ bool DeclContext::isInSpecializeExtensionContext() const {
    return isSpecializeExtensionContext(this);
 }
 
+bool DeclContext::isUnsupportedNestedProtocol() const {
+  return isa<ProtocolDecl>(this) && getParent()->isGenericContext();
+}
+
 bool DeclContext::isAlwaysAvailableConformanceContext() const {
   auto *ext = dyn_cast<ExtensionDecl>(this);
   if (ext == nullptr)

lib/Sema/TypeCheckType.cpp

@@ -531,6 +531,14 @@ Type TypeResolution::resolveTypeInContext(TypeDecl *typeDecl,
 
   assert(foundDC);
 
+  // Protocols cannot be nested in generic contexts. Use the declared interface
+  // type, which won't have a parent.
+  if (auto *proto = dyn_cast<ProtocolDecl>(typeDecl)) {
+    if (proto->isUnsupportedNestedProtocol()) {
+      return typeDecl->getDeclaredInterfaceType();
+    }
+  }
+
   // selfType is the self type of the context, unless the
   // context is a protocol type, in which case we might have
   // to use the existential type or superclass bound as a