go/types: add sizeof test

This is a direct port of CL 310530 to go/types, adjusted only for names
and to account for the smaller size of objects in go/types, due to
(I assume) token.Pos vs syntax.Pos.

Change-Id: I0cc34d56e41c1e66b17edd0ccd3f281d97a6b235
Reviewed-on: https://go-review.googlesource.com/c/go/+/312091
Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/sizeof_test.go

@@ -0,0 +1,63 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"reflect"
+	"testing"
+)
+
+// Signal size changes of important structures.
+func TestSizeof(t *testing.T) {
+	const _64bit = ^uint(0)>>32 != 0
+
+	var tests = []struct {
+		val    interface{} // type as a value
+		_32bit uintptr     // size on 32bit platforms
+		_64bit uintptr     // size on 64bit platforms
+	}{
+		// Types
+		{Basic{}, 16, 32},
+		{Array{}, 16, 24},
+		{Slice{}, 8, 16},
+		{Struct{}, 24, 48},
+		{Pointer{}, 8, 16},
+		{Tuple{}, 12, 24},
+		{Signature{}, 44, 88},
+		{_Sum{}, 12, 24},
+		{Interface{}, 60, 120},
+		{Map{}, 16, 32},
+		{Chan{}, 12, 24},
+		{Named{}, 64, 128},
+		{_TypeParam{}, 28, 48},
+		{instance{}, 44, 88},
+		{bottom{}, 0, 0},
+		{top{}, 0, 0},
+
+		// Objects
+		{PkgName{}, 48, 88},
+		{Const{}, 48, 88},
+		{TypeName{}, 40, 72},
+		{Var{}, 44, 80},
+		{Func{}, 44, 80},
+		{Label{}, 44, 80},
+		{Builtin{}, 44, 80},
+		{Nil{}, 40, 72},
+
+		// Misc
+		{Scope{}, 40, 80},
+		{Package{}, 40, 80},
+	}
+	for _, test := range tests {
+		got := reflect.TypeOf(test.val).Size()
+		want := test._32bit
+		if _64bit {
+			want = test._64bit
+		}
+		if got != want {
+			t.Errorf("unsafe.Sizeof(%T) = %d, want %d", test.val, got, want)
+		}
+	}
+}