reflect: implement Sizeof and Alignof for func values

This is a small change that appears to be necessary for encoding/json
support. It's simple enough to implement.

compiler/sizes.go

@@ -150,6 +150,9 @@ func (s *stdSizes) Sizeof(T types.Type) int64 {
 		return s.PtrSize * 2
 	case *types.Pointer:
 		return s.PtrSize
+	case *types.Signature:
+		// Func values in TinyGo are two words in size.
+		return s.PtrSize * 2
 	default:
 		panic("unknown type: " + t.String())
 	}

src/reflect/type.go

@@ -533,13 +533,16 @@ func (t rawType) Size() uintptr {
 	case Complex128:
 		return 16
 	case String:
-		return unsafe.Sizeof(StringHeader{})
+		return unsafe.Sizeof("")
 	case UnsafePointer, Chan, Map, Ptr:
 		return unsafe.Sizeof(uintptr(0))
 	case Slice:
-		return unsafe.Sizeof(SliceHeader{})
+		return unsafe.Sizeof([]int{})
 	case Interface:
 		return unsafe.Sizeof(interface{}(nil))
+	case Func:
+		var f func()
+		return unsafe.Sizeof(f)
 	case Array:
 		return t.elem().Size() * uintptr(t.Len())
 	case Struct:
@@ -579,13 +582,16 @@ func (t rawType) Align() int {
 	case Complex128:
 		return int(unsafe.Alignof(complex128(0)))
 	case String:
-		return int(unsafe.Alignof(StringHeader{}))
+		return int(unsafe.Alignof(""))
 	case UnsafePointer, Chan, Map, Ptr:
 		return int(unsafe.Alignof(uintptr(0)))
 	case Slice:
-		return int(unsafe.Alignof(SliceHeader{}))
+		return int(unsafe.Alignof([]int(nil)))
 	case Interface:
 		return int(unsafe.Alignof(interface{}(nil)))
+	case Func:
+		var f func()
+		return int(unsafe.Alignof(f))
 	case Struct:
 		numField := t.NumField()
 		alignment := 1

testdata/reflect.go

@@ -148,6 +148,7 @@ func main() {
 	assertSize(reflect.TypeOf(uintptr(0)).Size() == unsafe.Sizeof(uintptr(0)), "uintptr")
 	assertSize(reflect.TypeOf("").Size() == unsafe.Sizeof(""), "string")
 	assertSize(reflect.TypeOf(new(int)).Size() == unsafe.Sizeof(new(int)), "*int")
+	assertSize(reflect.TypeOf(zeroFunc).Size() == unsafe.Sizeof(zeroFunc), "func()")
 
 	// SetBool
 	rv := reflect.ValueOf(new(bool)).Elem()