Sema: Fix name lookup of nominal types nested inside a class from a protocol

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -274,8 +274,13 @@ Type TypeChecker::resolveTypeInContext(
 
   assert(foundDC);
 
+  // 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
+  // parent type instead.
   Type selfType;
-  if (isa<NominalTypeDecl>(typeDecl)) {
+  if (isa<NominalTypeDecl>(typeDecl) &&
+      typeDecl->getDeclContext()->getAsProtocolOrProtocolExtensionContext()) {
     // When looking up a nominal type declaration inside of a
     // protocol extension, always use the nominal type and
     // not the protocol 'Self' type.
@@ -292,7 +297,8 @@ Type TypeChecker::resolveTypeInContext(
 
     if (selfType->is<GenericTypeParamType>() &&
         typeDecl->getDeclContext()->getAsClassOrClassExtensionContext()) {
-      // We found a member of a class from a protocol extension.
+      // We found a member of a class from a protocol or protocol
+      // extension.
       //
       // Get the superclass of the 'Self' type parameter.
       auto *sig = foundDC->getGenericSignatureOfContext();

test/decl/ext/protocol.swift

@@ -237,6 +237,8 @@ protocol ConformedProtocol {
 class BaseWithAlias<T> : ConformedProtocol {
   typealias ConcreteAlias = T
 
+  struct NestedNominal {}
+
   func baseMethod(_: T) {}
 }
 
@@ -261,6 +263,8 @@ extension ExtendedProtocol where Self : DerivedWithAlias {
   func f3(x: AbstractConformanceAlias) {
     let _: DerivedWithAlias = x
   }
+
+  func f4(x: NestedNominal) {}
 }
 
 // ----------------------------------------------------------------------------

validation-test/compiler_crashers/28825-isa-classdecl-nominaldecl-expected-a-class-here.swift renamed to validation-test/compiler_crashers_fixed/28825-isa-classdecl-nominaldecl-expected-a-class-here.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol b:a{init(t:a}class a{class a