Reflection: Fix bug where presence of a no-payload enum resets field offsets back to zero for subsequent fields

The alignment was set to 0, which messed up the record layout
computations. Add an assert to catch this in the future.

Fixes <rdar://problem/29115967>.

Author: slavapestov

include/swift/Reflection/TypeLowering.h

@@ -117,7 +117,9 @@ class TypeInfo {
            unsigned Size, unsigned Alignment,
            unsigned Stride, unsigned NumExtraInhabitants)
     : Kind(Kind), Size(Size), Alignment(Alignment), Stride(Stride),
-      NumExtraInhabitants(NumExtraInhabitants) {}
+      NumExtraInhabitants(NumExtraInhabitants) {
+    assert(Alignment > 0);
+  }
 
   TypeInfoKind getKind() const { return Kind; }
 

stdlib/public/Reflection/TypeLowering.cpp

@@ -378,6 +378,8 @@ class ExistentialTypeInfoBuilder {
 unsigned RecordTypeInfoBuilder::addField(unsigned fieldSize,
                                          unsigned fieldAlignment,
                                          unsigned numExtraInhabitants) {
+  assert(fieldAlignment > 0);
+
   // Align the current size appropriately
   Size = ((Size + fieldAlignment - 1) & ~(fieldAlignment - 1));
 
@@ -873,7 +875,7 @@ class EnumTypeInfoBuilder {
 
 public:
   EnumTypeInfoBuilder(TypeConverter &TC)
-    : TC(TC), Size(0), Alignment(0), NumExtraInhabitants(0),
+    : TC(TC), Size(0), Alignment(1), NumExtraInhabitants(0),
       Kind(RecordKind::Invalid), Invalid(false) {}
 
   const TypeInfo *build(const TypeRef *TR, const FieldDescriptor *FD) {

test/Reflection/typeref_lowering.swift

@@ -913,11 +913,11 @@ V12TypeLowering10EnumStruct
 // CHECK-64: (struct TypeLowering.EnumStruct)
 // CHECK-64-NEXT: (struct size=81 alignment=8 stride=88 num_extra_inhabitants=0
 // CHECK-64-NEXT:   (field name=empty offset=0
-// CHECK-64-NEXT:     (no_payload_enum size=0 alignment=0 stride=1 num_extra_inhabitants=0))
+// CHECK-64-NEXT:     (no_payload_enum size=0 alignment=1 stride=1 num_extra_inhabitants=0))
 // CHECK-64-NEXT:   (field name=noPayload offset=0
-// CHECK-64-NEXT:     (no_payload_enum size=1 alignment=0 stride=1 num_extra_inhabitants=0))
-// CHECK-64-NEXT:   (field name=sillyNoPayload offset=0
-// CHECK-64-NEXT:     (no_payload_enum size=1 alignment=0 stride=1 num_extra_inhabitants=0))
+// CHECK-64-NEXT:     (no_payload_enum size=1 alignment=1 stride=1 num_extra_inhabitants=0))
+// CHECK-64-NEXT:   (field name=sillyNoPayload offset=1
+// CHECK-64-NEXT:     (no_payload_enum size=1 alignment=1 stride=1 num_extra_inhabitants=0))
 // CHECK-64-NEXT:   (field name=singleton offset=8
 // CHECK-64-NEXT:     (reference kind=strong refcounting=native))
 // CHECK-64-NEXT:   (field name=singlePayload offset=16