Change how array regions are serialized

proto/coroutine/v1/coroutine.proto

@@ -42,16 +42,15 @@ message Build {
 
 // Region is an encoded region of memory.
 message Region {
-  // Type is the type of the region.
+  // Type is the type of the region, shifted left by one.
+  //
+  // The least significant bit indicates that this region represents
+  // an array, and that the type is the array element type rather
+  // than the object that's encoded in this region.
   uint32 type = 1;
 
-  // Array length, when >= 0, indicates that this region is an
-  // array of the specified length (in terms of number of
-  // elements, not in terms of bytes) and that the region type
-  // is the type of the array element. If the array length is < 0
-  // then this region does not represent an array, and the region
-  // type describes the object that is encoded.
-  int32 array_length = 2;
+  // Array length, for regions that are arrays.
+  uint32 array_length = 2;
 
   // Data is the encoded contents of the memory region.
   bytes data = 3;

types/inspect.go

@@ -598,8 +598,8 @@ func (t *Region) Index() int {
 
 // Type is the type of the region.
 func (r *Region) Type() *Type {
-	t := r.state.Type(int(r.region.Type - 1))
-	if r.region.ArrayLength >= 0 {
+	t := r.state.Type(int((r.region.Type >> 1) - 1))
+	if r.region.Type&1 == 1 {
 		t = newArrayType(r.state, int64(r.region.ArrayLength), t)
 	}
 	return t

types/reflect.go

@@ -415,8 +415,11 @@ func serializePointedAt(s *Serializer, et reflect.Type, length int, p unsafe.Poi
 	}
 
 	region := &coroutinev1.Region{
-		Type:        s.types.ToType(r.typ),
-		ArrayLength: int32(r.len),
+		Type: s.types.ToType(r.typ) << 1,
+	}
+	if r.len >= 0 {
+		region.Type |= 1
+		region.ArrayLength = uint32(r.len)
 	}
 	s.regions = append(s.regions, region)
 
@@ -473,9 +476,9 @@ func deserializePointedAt(d *Deserializer, t reflect.Type, length int) unsafe.Po
 		}
 		region := d.regions[id-1]
 
-		regionType := d.types.ToReflect(typeid(region.Type))
+		regionType := d.types.ToReflect(typeid(region.Type >> 1))
 
-		if region.ArrayLength >= 0 {
+		if region.Type&1 == 1 {
 			elemSize := int(regionType.Size())
 			length := int(region.ArrayLength)
 			data := make([]byte, elemSize*length)
@@ -531,8 +534,7 @@ func serializeMapReflect(s *Serializer, t reflect.Type, r reflect.Value) {
 	size := r.Len()
 
 	region := &coroutinev1.Region{
-		Type:        s.types.ToType(t),
-		ArrayLength: -1, // not an array
+		Type: s.types.ToType(t) << 1,
 	}
 	s.regions = append(s.regions, region)
 

types/serde.go

@@ -58,9 +58,8 @@ func Serialize(x any) ([]byte, error) {
 		Strings:   s.strings.strings,
 		Regions:   s.regions,
 		Root: &coroutinev1.Region{
-			Type:        s.types.ToType(t),
-			ArrayLength: -1, // not an array
-			Data:        s.b,
+			Type: s.types.ToType(t) << 1,
+			Data: s.b,
 		},
 	}
 	return state.MarshalVT()