diff -r 449ed1afa056 -r ab0b8e388967 src/Pure/General/http.scala
--- a/src/Pure/General/http.scala	Thu Mar 15 11:27:32 2018 +0100
+++ b/src/Pure/General/http.scala	Thu Mar 15 11:44:07 2018 +0100
@@ -141,11 +141,7 @@
   val welcome: Handler =
     get("/", arg =>
       if (arg.uri.toString == "/") {
-        val id =
-          Isabelle_System.getenv("ISABELLE_ID") match {
-            case "" => Mercurial.repository(Path.explode("~~")).id()
-            case id => id
-          }
+        val id = Isabelle_System.isabelle_id()
         Some(Response.text("Welcome to Isabelle/" + id + ": " + Distribution.version))
       }
       else None)