Reflection: Give up instead of producing an empty field list if a field type does not demangle

Better to fail instead of producing an invalid layout.

Author: slavapestov

include/swift/Reflection/TypeRefBuilder.h

@@ -314,8 +314,8 @@ class TypeRefBuilder {
   const FieldDescriptor *getFieldTypeInfo(const TypeRef *TR);
 
   /// Get the parsed and substituted field types for a nominal type.
-  std::vector<FieldTypeInfo>
-  getFieldTypeRefs(const TypeRef *TR, const FieldDescriptor *FD);
+  bool getFieldTypeRefs(const TypeRef *TR, const FieldDescriptor *FD,
+                        std::vector<FieldTypeInfo> &Fields);
 
   /// Get the primitive type lowering for a builtin type.
   const BuiltinTypeDescriptor *getBuiltinTypeInfo(const TypeRef *TR);

stdlib/public/Reflection/TypeLowering.cpp

@@ -878,7 +878,13 @@ class EnumTypeInfoBuilder {
     unsigned NoPayloadCases = 0;
     std::vector<FieldTypeInfo> PayloadCases;
 
-    for (auto Case : TC.getBuilder().getFieldTypeRefs(TR, FD)) {
+    std::vector<FieldTypeInfo> Fields;
+    if (!TC.getBuilder().getFieldTypeRefs(TR, FD, Fields)) {
+      Invalid = true;
+      return nullptr;
+    }
+
+    for (auto Case : Fields) {
       if (Case.TR == nullptr) {
         NoPayloadCases++;
         continue;
@@ -1024,7 +1030,12 @@ class LowerType
       // Lower the struct's fields using substitutions from the
       // TypeRef to make field types concrete.
       RecordTypeInfoBuilder builder(TC, RecordKind::Struct);
-      for (auto Field : TC.getBuilder().getFieldTypeRefs(TR, FD))
+
+      std::vector<FieldTypeInfo> Fields;
+      if (!TC.getBuilder().getFieldTypeRefs(TR, FD, Fields))
+        return nullptr;
+
+      for (auto Field : Fields)
         builder.addField(Field.Name, Field.TR);
       return builder.build();
     }
@@ -1266,11 +1277,15 @@ const TypeInfo *TypeConverter::getClassInstanceTypeInfo(const TypeRef *TR,
     // TypeRef to make field types concrete.
     RecordTypeInfoBuilder builder(*this, RecordKind::ClassInstance);
 
+    std::vector<FieldTypeInfo> Fields;
+    if (!getBuilder().getFieldTypeRefs(TR, FD, Fields))
+      return nullptr;
+
     // Start layout from the given instance start offset. This should
     // be the superclass instance size.
     builder.addField(start, 1, /*numExtraInhabitants=*/0);
 
-    for (auto Field : getBuilder().getFieldTypeRefs(TR, FD))
+    for (auto Field : Fields)
       builder.addField(Field.Name, Field.TR);
     return builder.build();
   }

stdlib/public/Reflection/TypeRefBuilder.cpp

@@ -124,15 +124,16 @@ TypeRefBuilder::getFieldTypeInfo(const TypeRef *TR) {
   return nullptr;
 }
 
-std::vector<FieldTypeInfo>
-TypeRefBuilder::getFieldTypeRefs(const TypeRef *TR, const FieldDescriptor *FD) {
+
+bool TypeRefBuilder::getFieldTypeRefs(const TypeRef *TR,
+                                      const FieldDescriptor *FD,
+                                      std::vector<FieldTypeInfo> &Fields) {
   if (FD == nullptr)
-    return {};
+    return false;
 
   auto Subs = TR->getSubstMap();
 
   Demangle::Demangler Dem;
-  std::vector<FieldTypeInfo> Fields;
   for (auto &Field : *FD) {
     auto FieldName = Field.getFieldName();
 
@@ -145,7 +146,7 @@ TypeRefBuilder::getFieldTypeRefs(const TypeRef *TR, const FieldDescriptor *FD) {
     auto Demangled = Dem.demangleType(Field.getMangledTypeName());
     auto Unsubstituted = swift::remote::decodeMangledType(*this, Demangled);
     if (!Unsubstituted)
-      return {};
+      return false;
 
     auto Substituted = Unsubstituted->subst(*this, Subs);
 
@@ -156,7 +157,7 @@ TypeRefBuilder::getFieldTypeRefs(const TypeRef *TR, const FieldDescriptor *FD) {
 
     Fields.push_back(FieldTypeInfo::forField(FieldName, Substituted));
   }
-  return Fields;
+  return true;
 }
 
 const BuiltinTypeDescriptor *