godoc: don't drop the query params when redirecting

http://golang.org/issue/new?title=Title was being redirected to
https://github.com/golang/go/issues/new. The CL preserves the
query parameters during direct.

Change-Id: I3057ccd5304b00df53b664b71ea35ea05d313aa4
Reviewed-on: https://go-review.googlesource.com/15431
Reviewed-by: Andrew Gerrand <adg@golang.org>

godoc/redirect/redirect.go

@@ -142,7 +142,11 @@ var prefixHelpers = map[string]string{
 
 func Handler(target string) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		http.Redirect(w, r, target, http.StatusMovedPermanently)
+		url := target
+		if qs := r.URL.RawQuery; qs != "" {
+			url += "?" + qs
+		}
+		http.Redirect(w, r, url, http.StatusMovedPermanently)
 	})
 }
 

godoc/redirect/redirect_test.go

@@ -41,10 +41,12 @@ func TestRedirects(t *testing.T) {
 		"/change/a": {302, "https://go.googlesource.com/go/+/a"},
 
 		"/issue":                    {301, "https://github.com/golang/go/issues"},
-		"/issues":       {301, "https://github.com/golang/go/issues"},
+		"/issue?":                   {301, "https://github.com/golang/go/issues"},
 		"/issue/1":                  {302, "https://github.com/golang/go/issues/1"},
-		"/issues/1":     {302, "https://github.com/golang/go/issues/1"},
 		"/issue/new":                {301, "https://github.com/golang/go/issues/new"},
+		"/issue/new?a=b&c=d%20&e=f": {301, "https://github.com/golang/go/issues/new?a=b&c=d%20&e=f"},
+		"/issues":                   {301, "https://github.com/golang/go/issues"},
+		"/issues/1":                 {302, "https://github.com/golang/go/issues/1"},
 		"/issues/new":               {301, "https://github.com/golang/go/issues/new"},
 		"/issues/1/2/3":             errorResult(404),