godoc: added -index flag to enable/disable search index

Fixes #1647.

R=adg, rsc1, r2, rsc, r
CC=golang-dev
https://golang.org/cl/4444083

lib/godoc/godoc.html

@@ -33,7 +33,9 @@
         <a href="/pkg/">Packages</a> <span class="sep">|</span>
         <a href="/cmd/">Commands</a> <span class="sep">|</span>
         <a href="/doc/go_spec.html">Specification</a>
+	{.section SearchBox}
         <input id="search" type="search" name="q" value="{.section Query}{Query|html-esc}{.end}" class="{.section Query}{.or}inactive{.end}" placeholder="code search" results="0" />
+	{.end}
         </form>
       </div>
     </div>

src/cmd/godoc/doc.go

@@ -47,6 +47,9 @@ The flags are:
 		width of tabs in units of spaces
 	-timestamps=true
 		show timestamps with directory listings
+	-index
+		enable identifier and full text search index
+		(no search box is shown if -index is not set)
 	-maxresults=10000
 		maximum number of full text search results shown
 		(no full text index is built if maxresults <= 0)

src/cmd/godoc/godoc.go

@@ -64,9 +64,12 @@ var (
 	// layout control
 	tabwidth       = flag.Int("tabwidth", 4, "tab width")
 	showTimestamps = flag.Bool("timestamps", true, "show timestamps with directory listings")
-	maxResults     = flag.Int("maxresults", 10000, "maximum number of full text search results shown")
 	templateDir    = flag.String("templates", "", "directory containing alternate template files")
 
+	// search index
+	indexEnabled = flag.Bool("index", false, "enable search index")
+	maxResults   = flag.Int("maxresults", 10000, "maximum number of full text search results shown")
+
 	// file system mapping
 	fsMap      Mapping // user-defined mapping
 	fsTree     RWValue // *Directory tree of packages, updated with each sync
@@ -690,6 +693,7 @@ func servePage(w http.ResponseWriter, title, subtitle, query string, content []b
 		Title     string
 		Subtitle  string
 		PkgRoots  []string
+		SearchBox bool
 		Query     string
 		Version   string
 		Menu      []byte
@@ -698,6 +702,7 @@ func servePage(w http.ResponseWriter, title, subtitle, query string, content []b
 		title,
 		subtitle,
 		fsMap.PrefixList(),
+		*indexEnabled,
 		query,
 		runtime.Version(),
 		nil,
@@ -1174,12 +1179,16 @@ func lookup(query string) (result SearchResult) {
 	}
 
 	// is the result accurate?
+	if *indexEnabled {
 		if _, ts := fsModified.get(); timestamp < ts {
 			// The index is older than the latest file system change
 			// under godoc's observation. Indexing may be in progress
 			// or start shortly (see indexer()).
 			result.Alert = "Indexing in progress: result may be inaccurate"
 		}
+	} else {
+		result.Alert = "Search index disabled: no results available"
+	}
 
 	return
 }

src/cmd/godoc/main.go

@@ -246,8 +246,13 @@ func main() {
 			log.Printf("address = %s", *httpAddr)
 			log.Printf("goroot = %s", *goroot)
 			log.Printf("tabwidth = %d", *tabwidth)
-			if *maxResults > 0 {
-				log.Printf("maxresults = %d (full text index enabled)", *maxResults)
+			switch {
+			case !*indexEnabled:
+				log.Print("search index disabled")
+			case *maxResults > 0:
+				log.Printf("full text index enabled (maxresults = %d)", *maxResults)
+			default:
+				log.Print("identifier search index enabled")
 			}
 			if !fsMap.IsEmpty() {
 				log.Print("user-defined mapping:")
@@ -284,7 +289,9 @@ func main() {
 		}
 
 		// Start indexing goroutine.
+		if *indexEnabled {
 			go indexer()
+		}
 
 		// Start http server.
 		if err := http.ListenAndServe(*httpAddr, handler); err != nil {