- don't call String method of AST nodes when converting them to text

- make token.Position.String more robust

TBR=rsc
DELTA=20  (10 added, 6 deleted, 4 changed)
OCL=32564
CL=32564

src/cmd/godoc/godoc.go

@@ -213,19 +213,21 @@ func nodeText(node interface{}) []byte {
 
 // Convert x, whatever it is, to text form.
 func toText(x interface{}) []byte {
-	type String interface { String() string }
+	type Stringer interface { String() string }
 
 	switch v := x.(type) {
 	case []byte:
 		return v;
 	case string:
 		return strings.Bytes(v);
-	case String:
-		return strings.Bytes(v.String());
 	case ast.Decl:
 		return nodeText(v);
 	case ast.Expr:
 		return nodeText(v);
+	case Stringer:
+		// last resort (AST nodes get a String method
+		// from token.Position - don't call that one)
+		return strings.Bytes(v.String());
 	}
 	var buf bytes.Buffer;
 	fmt.Fprint(&buf, x);

src/pkg/go/token/token.go

@@ -353,6 +353,7 @@ func (pos *Position) IsValid() bool {
 
 
 func (pos *Position) String() string {
+	if pos != nil {
 		s := pos.Filename;
 		if pos.IsValid() {
 			if s != "" {
@@ -363,5 +364,6 @@ func (pos *Position) String() string {
 		if s != "" {
 			return s;
 		}
+	}
 	return "<unknown position>";
 }