go/ast: print CommentMap contents in source order

Sort the comment map entries before printing.
Makes it easier to use the output for debugging.

For #39753.

Change-Id: Ic8e7d27dd2df59173e2c3a04a6b71ae966703885
Reviewed-on: https://go-review.googlesource.com/c/go/+/315370
Trust: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: griesemer

src/go/ast/commentmap.go

@@ -315,9 +315,17 @@ loop:
 }
 
 func (cmap CommentMap) String() string {
+	// print map entries in sorted order
+	var nodes []Node
+	for node := range cmap {
+		nodes = append(nodes, node)
+	}
+	sort.Sort(byInterval(nodes))
+
 	var buf bytes.Buffer
 	fmt.Fprintln(&buf, "CommentMap {")
-	for node, comment := range cmap {
+	for _, node := range nodes {
+		comment := cmap[node]
 		// print name of identifiers; print node type for other nodes
 		var s string
 		if ident, ok := node.(*Ident); ok {