ast: make ExampleCommentMap a runnable example

Fixes #20450

Change-Id: I2256282a8880e99508e98fefedfb94a7cccacbcf
Reviewed-on: https://go-review.googlesource.com/48969
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

diff --git a/src/go/ast/example_test.go b/src/go/ast/example_test.go
index d2e734f2cbec0974df7ec0c5a1747d7df73dd78b..52a77981b81935532c59c3fb89ca5181a64b4621 100644 (file)
--- a/src/go/ast/example_test.go
+++ b/src/go/ast/example_test.go
@@ -44,7 +44,7 @@ var X = f(3.14)*2 + c
                return true
        })
 
-       // output:
+       // Output:
        // src.go:2:9:  p
        // src.go:3:7:  c
        // src.go:3:11: 1.0
@@ -75,7 +75,7 @@ func main() {
        // Print the AST.
        ast.Print(fset, f)
 
-       // output:
+       // Output:
        //      0  *ast.File {
        //      1  .  Package: 2:1
        //      2  .  Name: *ast.Ident {
@@ -172,7 +172,12 @@ func main() {
        cmap := ast.NewCommentMap(fset, f, f.Comments)
 
        // Remove the first variable declaration from the list of declarations.
-       f.Decls = removeFirstVarDecl(f.Decls)
+       for i, decl := range f.Decls {
+               if gen, ok := decl.(*ast.GenDecl); ok && gen.Tok == token.VAR {
+                       copy(f.Decls[i:], f.Decls[i+1:])
+                       f.Decls = f.Decls[:len(f.Decls)-1]
+               }
+       }
 
        // Use the comment map to filter comments that don't belong anymore
        // (the comments associated with the variable declaration), and create
@@ -186,7 +191,7 @@ func main() {
        }
        fmt.Printf("%s", buf.Bytes())
 
-       // output:
+       // Output:
        // // This is the package comment.
        // package main
        //
@@ -198,13 +203,3 @@ func main() {
        //      fmt.Println(hello) // line comment 3
        // }
 }
-
-func removeFirstVarDecl(list []ast.Decl) []ast.Decl {
-       for i, decl := range list {
-               if gen, ok := decl.(*ast.GenDecl); ok && gen.Tok == token.VAR {
-                       copy(list[i:], list[i+1:])
-                       return list[:len(list)-1]
-               }
-       }
-       panic("variable declaration not found")
-}