cmd/gotype: make it compile against Go 1.8 and earlier

types.SizesFor was introduced for Go 1.9. Need to provide
a local implementation to have gotype build against earlier
versions.

Fixes golang/go#19545.

Change-Id: I6fdbe414e6574eda00c01295b666230daff2dfdc
Reviewed-on: https://go-review.googlesource.com/38157
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

cmd/gotype/gotype.go

@@ -2,15 +2,18 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// gotype.go is a 1:1 copy of the original source maintained in
-// $GOROOT/src/go/types/gotype.go.
+// gotype.go is a copy of the original source maintained
+// in $GOROOT/src/go/types/gotype.go, but with the call
+// to types.SizesFor factored out so we can provide a local
+// implementation when compiling against Go 1.8 and earlier.
 //
-// This copy is here for the sole purpose of satisfying existing
+// This code is here for the sole purpose of satisfying historic
 // references to this location, and for making gotype accessible
 // via 'go get'.
 //
 // Do NOT make changes to this version as they will not be maintained
-// (and possibly overwritten). Any changes should be made to the original.
+// (and possibly overwritten). Any changes should be made to the original
+// and then ported to here.
 
 /*
 The gotype command, like the front-end of a Go compiler, parses and
@@ -282,7 +285,7 @@ func checkPkgFiles(files []*ast.File) {
 			report(err)
 		},
 		Importer: importer.For(*compiler, nil),
-		Sizes:    types.SizesFor(build.Default.Compiler, build.Default.GOARCH),
+		Sizes:    SizesFor(build.Default.Compiler, build.Default.GOARCH),
 	}
 
 	defer func() {

cmd/gotype/sizesFor18.go

@@ -0,0 +1,38 @@
+// Copyright 2017 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.
+
+// +build !go1.9
+
+// This file contains a copy of the implementation of types.SizesFor
+// since this function is not available in go/types before Go 1.9.
+
+package main
+
+import "go/types"
+
+var gcArchSizes = map[string]*types.StdSizes{
+	"386":      {4, 4},
+	"arm":      {4, 4},
+	"arm64":    {8, 8},
+	"amd64":    {8, 8},
+	"amd64p32": {4, 8},
+	"mips":     {4, 4},
+	"mipsle":   {4, 4},
+	"mips64":   {8, 8},
+	"mips64le": {8, 8},
+	"ppc64":    {8, 8},
+	"ppc64le":  {8, 8},
+	"s390x":    {8, 8},
+}
+
+func SizesFor(compiler, arch string) types.Sizes {
+	if compiler != "gc" {
+		return nil
+	}
+	s, ok := gcArchSizes[arch]
+	if !ok {
+		return nil
+	}
+	return s
+}

cmd/gotype/sizesFor19.go

@@ -0,0 +1,13 @@
+// Copyright 2017 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.
+
+// +build go1.9
+
+package main
+
+import "go/types"
+
+func SizesFor(compiler, arch string) types.Sizes {
+	return types.SizesFor(compiler, arch)
+}