godoc: Implement Unordered Output.

When an Example's output is listed as being Unordered this will make
godoc display "Unordered output:" rather than the normal "Output:".

For an example of where this is useful, see the recently added example
for math.rand.Perm().

Change-Id: I737c901102dca46434f46a48300445bb43ce34e0
Reviewed-on: https://go-review.googlesource.com/20458
Reviewed-by: Andrew Gerrand <adg@golang.org>

godoc/godoc.go

@@ -491,8 +491,8 @@ func (p *Presentation) example_htmlFunc(info *PageInfo, funcName string) string
 
 		err := p.ExampleHTML.Execute(&buf, struct {
 			Name, Doc, Code, Play, Output string
-			Share                         bool
-		}{eg.Name, eg.Doc, code, play, out, info.Share})
+			Share, Unordered              bool
+		}{eg.Name, eg.Doc, code, play, out, info.Share, eg.Unordered})
 		if err != nil {
 			log.Print(err)
 		}
@@ -587,7 +587,7 @@ func startsWithUppercase(s string) bool {
 	return unicode.IsUpper(r)
 }
 
-var exampleOutputRx = regexp.MustCompile(`(?i)//[[:space:]]*output:`)
+var exampleOutputRx = regexp.MustCompile(`(?i)//([[:space:]]*unordered)?[[:space:]]*output:`)
 
 // stripExampleSuffix strips lowercase braz in Foo_braz or Foo_Bar_braz from name
 // while keeping uppercase Braz in Foo_Braz.

godoc/static/example.html

@@ -22,7 +22,11 @@
 			<p>Code:</p>
 			<pre class="code">{{.Code}}</pre>
 			{{with .Output}}
+			{{if $.Unordered}}
+			<p>Unordered Output:</p>
+			{{else}}
 			<p>Output:</p>
+			{{end}}
 			<pre class="output">{{html .}}</pre>
 			{{end}}
 		{{end}}

godoc/static/static.go

@@ -450,7 +450,11 @@ var Files = map[string]string{
 			<p>Code:</p>
 			<pre class="code">{{.Code}}</pre>
 			{{with .Output}}
+			{{if $.Unordered}}
+			<p>Unordered Output:</p>
+			{{else}}
 			<p>Output:</p>
+			{{end}}
 			<pre class="output">{{html .}}</pre>
 			{{end}}
 		{{end}}