go.tools/go/types: print interface methods in sorted order

Required for testing code of clients.

R=adonovan
CC=golang-dev
https://golang.org/cl/35940049

go/types/objects.go

@@ -48,7 +48,11 @@ func Id(pkg *Package, name string) string {
 		return name
 	}
 	// unexported names need the package path for differentiation
-	path := ""
+	// (if there's no package, make sure we don't start with '.'
+	// as that may change the order of methods between a setup
+	// inside a package and outside a package - which breaks some
+	// tests)
+	path := "_"
 	// TODO(gri): shouldn't !ast.IsExported(name) => pkg != nil be an precondition?
 	// if pkg == nil {
 	// 	panic("nil package in lookup of unexported name")
@@ -56,7 +60,7 @@ func Id(pkg *Package, name string) string {
 	if pkg != nil {
 		path = pkg.path
 		if path == "" {
-			path = "?"
+			path = "_"
 		}
 	}
 	return path + "." + name

go/types/typestring.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"fmt"
 	"go/ast"
+	"sort"
 )
 
 // TypeString returns the string representation of typ.
@@ -84,7 +85,19 @@ func WriteType(buf *bytes.Buffer, this *Package, typ Type) {
 		//     }
 		//
 		buf.WriteString("interface{")
-		for i, m := range t.methods {
+		// Sort methods instead of printing them in source order.
+		// This is needed at the moment because interfaces are
+		// created by providing the list of source methods and
+		// embedded interfaces, but only have an accessor to the list
+		// of all methods (which is sorted by name). By sorting here
+		// we guarantee that the list is printed the same independent
+		// of how the Interface was created.
+		// TODO(gri) remove this extra step once we have the complete
+		// set of accessors for Interface.
+		var methods []*Func
+		methods = append(methods, t.methods...) // make a copy
+		sort.Sort(byUniqueMethodName(methods))
+		for i, m := range methods {
 			if i > 0 {
 				buf.WriteString("; ")
 			}