Allow a nil Ident to print without crashing.

Allow Walk of []Decl

R=gri
CC=golang-dev, rsc
https://golang.org/cl/183112

src/pkg/go/ast/ast.go

@@ -357,7 +357,12 @@ func IsExported(name string) bool {
 // (i.e., whether it begins with an uppercase letter).
 func (name *Ident) IsExported() bool { return IsExported(name.Value) }
 
-func (name *Ident) String() string { return name.Value }
+func (name *Ident) String() string {
+	if name != nil {
+		return name.Value
+	}
+	return "<nil>"
+}
 
 
 // ----------------------------------------------------------------------------
@@ -598,7 +603,7 @@ type (
 	TypeSpec struct {
 		Doc     *CommentGroup // associated documentation; or nil
 		Name    *Ident        // type name
-		Type    Expr
+		Type    Expr          // *ArrayType, *StructType, *FuncType, *InterfaceType, *MapType, *ChanType or *Ident
 		Comment *CommentGroup // line comments; or nil
 	}
 )

src/pkg/go/ast/walk.go

@@ -41,7 +41,7 @@ func walkBlockStmt(v Visitor, b *BlockStmt) {
 // followed by a call of w.Visit(nil).
 //
 // Walk may be called with any of the named ast node types. It also
-// accepts arguments of type []*Field, []*Ident, []Expr and []Stmt;
+// accepts arguments of type []*Field, []*Ident, []Expr, []Stmt and []Decl;
 // the respective children are the slice elements.
 //
 func Walk(v Visitor, node interface{}) {
@@ -291,9 +291,7 @@ func Walk(v Visitor, node interface{}) {
 	case *File:
 		walkCommentGroup(v, n.Doc)
 		walkIdent(v, n.Name)
-		for _, d := range n.Decls {
-			Walk(v, d)
-		}
+		Walk(v, n.Decls)
 		walkCommentGroup(v, n.Comments)
 
 	case *Package:
@@ -321,6 +319,11 @@ func Walk(v Visitor, node interface{}) {
 			Walk(v, x)
 		}
 
+	case []Decl:
+		for _, x := range n {
+			Walk(v, x)
+		}
+
 	default:
 		fmt.Printf("ast.Walk: unexpected type %T", n)
 		panic()