playground: redirect https://play.golang.org/ to https://go.dev/play

The Go web sites are consolidating into go.dev,
including the playground at https://go.dev/play.
Redirect users (but not API requests) to the new URL.

Change-Id: I9bc4338568d1afd5916a84ec4d26cce2133b9ea0
Reviewed-on: https://go-review.googlesource.com/c/playground/+/364816
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

Author: rsc

edit.go

@@ -78,11 +78,17 @@ func (s *server) handleEdit(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 	}
+
+	if r.Host == hostname {
+		// The main playground is now on go.dev/play.
+		http.Redirect(w, r, "https://go.dev/play"+r.URL.Path, http.StatusFound)
+		return
+	}
+
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	data := &editData{
 		Snippet:   snip,
 		Share:     allowShare(r),
-		Analytics: r.Host == hostname,
 		GoVersion: runtime.Version(),
 		Gotip:     s.gotip,
 		Examples:  s.examples.examples,

server_test.go

@@ -72,7 +72,7 @@ func TestEdit(t *testing.T) {
 		{"foo.play.golang.org to play.golang.org", http.MethodGet, "https://foo.play.golang.org", http.StatusFound, map[string]string{"Location": "https://play.golang.org"}, nil},
 		{"Non-existent page", http.MethodGet, "https://play.golang.org/foo", http.StatusNotFound, nil, nil},
 		{"Unknown snippet", http.MethodGet, "https://play.golang.org/p/foo", http.StatusNotFound, nil, nil},
-		{"Existing snippet", http.MethodGet, "https://play.golang.org/p/" + id, http.StatusOK, nil, nil},
+		{"Existing snippet", http.MethodGet, "https://play.golang.org/p/" + id, http.StatusFound, nil, nil},
 		{"Plaintext snippet", http.MethodGet, "https://play.golang.org/p/" + id + ".go", http.StatusOK, nil, barBody},
 		{"Download snippet", http.MethodGet, "https://play.golang.org/p/" + id + ".go?download=true", http.StatusOK, map[string]string{"Content-Disposition": fmt.Sprintf(`attachment; filename="%s.go"`, id)}, barBody},
 	}