[Reflection] Add support for imported structs with recorded fields

Update IRGen to trigger generation of type metadata for foreign
struct types found in fields. And fix TypeRefBuilder to handle
the case where struct has fields but at the same time has opaque
metadata.

Author: xedin

include/swift/Reflection/Records.h

@@ -186,6 +186,10 @@ class FieldDescriptor {
             Kind == FieldDescriptorKind::ObjCProtocol);
   }
 
+  bool isStruct() const {
+    return Kind == FieldDescriptorKind::Struct;
+  }
+
   const_iterator begin() const {
     auto Begin = getFieldRecordBuffer();
     auto End = Begin + NumFields;

stdlib/public/Reflection/TypeLowering.cpp

@@ -1057,16 +1057,18 @@ class LowerType
 
   const TypeInfo *visitAnyNominalTypeRef(const TypeRef *TR) {
     const auto &FD = TC.getBuilder().getFieldTypeInfo(TR);
-    if (FD.first == nullptr) {
+    if (FD.first == nullptr || FD.first->isStruct()) {
       // Maybe this type is opaque -- look for a builtin
       // descriptor to see if we at least know its size
       // and alignment.
       if (auto ImportedTypeDescriptor = TC.getBuilder().getBuiltinTypeInfo(TR))
         return TC.makeTypeInfo<BuiltinTypeInfo>(ImportedTypeDescriptor);
 
       // Otherwise, we're out of luck.
-      DEBUG(std::cerr << "No TypeInfo for nominal type: "; TR->dump());
-      return nullptr;
+      if (FD.first == nullptr) {
+        DEBUG(std::cerr << "No TypeInfo for nominal type: "; TR->dump());
+        return nullptr;
+      }
     }
 
     switch (FD.first->Kind) {

test/Reflection/typeref_decoding_imported.swift

@@ -20,6 +20,19 @@
 // CHECK-32: mce: __C.MyCEnum
 // CHECK-32: (struct __C.MyCEnum)
 
+// CHECK-32: __C.MyCStruct
+// CHECK-32: -------------
+// CHECK-32: i: Swift.Int32
+// CHECK-32: (struct Swift.Int32)
+
+// CHECK-32: ip: Swift.Optional<Swift.UnsafeMutablePointer<Swift.Int32>>
+// CHECK-32: (bound_generic_enum Swift.Optional
+// CHECK-32:   (bound_generic_struct Swift.UnsafeMutablePointer
+// CHECK-32:     (struct Swift.Int32)))
+
+// CHECK-32: c: Swift.Int8
+// CHECK-32: (struct Swift.Int8)
+
 // CHECK-32: TypesToReflect.AlsoHasCTypes
 // CHECK-32: ----------------------------
 
@@ -82,6 +95,19 @@
 // CHECK-64: mcu: __C.MyCUnion
 // CHECK-64: (struct __C.MyCUnion)
 
+// CHECK-64: __C.MyCStruct
+// CHECK-64: -------------
+// CHECK-64: i: Swift.Int32
+// CHECK-64: (struct Swift.Int32)
+
+// CHECK-64: ip: Swift.Optional<Swift.UnsafeMutablePointer<Swift.Int32>>
+// CHECK-64: (bound_generic_enum Swift.Optional
+// CHECK-64:   (bound_generic_struct Swift.UnsafeMutablePointer
+// CHECK-64:     (struct Swift.Int32)))
+
+// CHECK-64: c: Swift.Int8
+// CHECK-64: (struct Swift.Int8)
+
 // CHECK-64: TypesToReflect.AlsoHasCTypes
 // CHECK-64: ----------------------------