analysis: add readme text on empty search

Change-Id: I1d0d574a78559f08125d8aa03ea4f6ab7912e28c
Reviewed-on: https://go-review.googlesource.com/36028Reviewed-by: Russ Cox <rsc@golang.org>

analysis/app/app.go

@@ -20,6 +20,7 @@ type App struct {
 
 // RegisterOnMux registers the app's URLs on mux.
 func (a *App) RegisterOnMux(mux *http.ServeMux) {
+	mux.HandleFunc("/", a.index)
 	mux.HandleFunc("/search", a.search)
 	mux.HandleFunc("/compare", a.compare)
 }
@@ -37,3 +38,8 @@ func (a *App) search(w http.ResponseWriter, r *http.Request) {
 	//q := r.Form.Get("q")
 	a.compare(w, r)
 }
+
+// index redirects / to /search.
+func (a *App) index(w http.ResponseWriter, r *http.Request) {
+	http.Redirect(w, r, "/search", http.StatusSeeOther)
+}

analysis/app/compare.go

@@ -222,6 +222,10 @@ func elideKeyValues(content string, keys map[string]bool) string {
 }
 
 func (a *App) compareQuery(q string) *compareData {
+	if len(q) == 0 {
+		return &compareData{}
+	}
+
 	// Parse query
 	prefix, queries := parseQueryString(q)
 

analysis/appengine/template/compare.html

@@ -89,6 +89,16 @@ td.count {
       </form>
     </div>
     <div id="results">
+      {{if not .Q}}
+        <p>The Go Performance Dashboard provides a centralized
+          resource for sharing and analyzing benchmark results. To get
+          started, upload benchmark results using
+          <code>go get -u golang.org/x/perf/cmd/benchsave</code>
+          and
+          <code>benchsave old.txt new.txt</code>
+          or upload via the web at
+          <a href="https://perfdata-dot-golang-org.appspot.com/upload">https://perfdata-dot-golang-org.appspot.com/upload</a>.</p>
+      {{else}}
         {{with .Error}}
         <p>{{.}}</p>
         {{else}}
@@ -148,6 +158,7 @@ td.count {
             {{.Benchstat}}
           </div>
         {{end}}
+      {{end}}
     </div>
   </body>
 </html>