AST: Fix mangling of nominal types with a type alias parent type

The mangling AST cannot represent this, and we were incorrectly
pulling generic arguments from the type alias type. Instead let's
just desugar the parent type when mangling a nominal type.

Fixes <rdar://problem/45900947>.

Author: slavapestov

lib/AST/ASTMangler.cpp

@@ -679,20 +679,10 @@ static bool shouldMangleAsGeneric(Type type) {
   if (!type)
     return false;
 
-  TypeBase *typePtr = type.getPointer();
-  if (auto typeAlias = dyn_cast<NameAliasType>(typePtr))
+  if (auto typeAlias = dyn_cast<NameAliasType>(type.getPointer()))
     return !typeAlias->getSubstitutionMap().empty();
 
-  if (auto bound = dyn_cast<BoundGenericType>(typePtr))
-    return true;
-
-  if (auto nominal = dyn_cast<NominalType>(typePtr))
-    return shouldMangleAsGeneric(nominal->getParent());
-
-  if (auto unbound = dyn_cast<UnboundGenericType>(typePtr))
-    return shouldMangleAsGeneric(unbound->getParent());
-
-  return false;
+  return type->isSpecialized();
 }
 
 /// Mangle a type into the buffer.
@@ -1110,15 +1100,15 @@ void ASTMangler::appendBoundGenericArgs(Type type, bool &isFirstArgList) {
 
   if (auto *unboundType = dyn_cast<UnboundGenericType>(typePtr)) {
     if (Type parent = unboundType->getParent())
-      appendBoundGenericArgs(parent, isFirstArgList);
+      appendBoundGenericArgs(parent->getDesugaredType(), isFirstArgList);
   } else if (auto *nominalType = dyn_cast<NominalType>(typePtr)) {
     if (Type parent = nominalType->getParent())
-      appendBoundGenericArgs(parent, isFirstArgList);
+      appendBoundGenericArgs(parent->getDesugaredType(), isFirstArgList);
   } else {
     auto boundType = cast<BoundGenericType>(typePtr);
     genericArgs = boundType->getGenericArgs();
     if (Type parent = boundType->getParent())
-      appendBoundGenericArgs(parent, isFirstArgList);
+      appendBoundGenericArgs(parent->getDesugaredType(), isFirstArgList);
   }
   if (isFirstArgList) {
     appendOperator("y");

test/DebugInfo/typealias.swift

@@ -19,6 +19,19 @@ struct Generic<T> {
 }
 
 typealias Specific = Generic<Int>
+typealias NotSpecific<T> = Generic<T>.Inner
+
+struct Outer : P {
+  enum Inner {
+    case x
+  }
+}
+
+protocol P {
+  typealias T = Outer
+}
+
+// CHECK-DAG: [[INNER_TYPE:![0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type{{.*}} identifier: "$s9typealias5OuterV5InnerOD"
 
 func main () {
   // CHECK-DAG: !DILocalVariable(name: "a",{{.*}} type: ![[DIEOFFSET]]
@@ -33,9 +46,23 @@ func main () {
   markUsed(c);
 
   // CHECK-DAG: !DILocalVariable(name: "d", {{.*}} type: [[NONGENERIC_TYPE:![0-9]+]])
-  // CHECK: [[NONGENERIC_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type{{.*}} identifier: "$s9typealias7GenericV5InnerOD"
+  // CHECK: [[NONGENERIC_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type{{.*}} identifier: "$s9typealias7GenericV5InnerOySi_GD"
   let d: Specific.Inner = .value
   markUsed(d)
+
+  // CHECK-DAG: !DILocalVariable(name: "e", {{.*}} type: [[INNER_TYPE]])
+  let e: Outer.T.Inner = .x
+  markUsed(e)
+
+  // CHECK-DAG: !DILocalVariable(name: "f", {{.*}} type: [[OUTER_T_TYPE:![0-9]+]])
+  // CHECK: [[OUTER_T_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$s9typealias1PP1TayAA5OuterV_GD"
+  let f: Outer.T = Outer()
+  markUsed(f)
+
+  // CHECK-DAG: !DILocalVariable(name: "g", {{.*}} type: [[GENERIC_TYPE:![0-9]+]])
+  // CHECK: [[GENERIC_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$s9typealias11NotSpecificaySiGD"
+  let g: NotSpecific<Int> = .value
+  markUsed(g)
 }
 
-main();
+main()