go/ast: fix walk to handle "for range x"

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/117790043

diff --git a/src/pkg/go/ast/walk.go b/src/pkg/go/ast/walk.go
index fedffb3f22f8d95395cace9b6455832e4d77d0c4..73ac38647a23f2d6b7417428fb61659b2efe512d 100644 (file)
--- a/src/pkg/go/ast/walk.go
+++ b/src/pkg/go/ast/walk.go
@@ -275,7 +275,9 @@ func Walk(v Visitor, node Node) {
                Walk(v, n.Body)
 
        case *RangeStmt:
-               Walk(v, n.Key)
+               if n.Key != nil {
+                       Walk(v, n.Key)
+               }
                if n.Value != nil {
                        Walk(v, n.Value)
                }