src/Pure/PIDE/prover.scala

--- a/src/Pure/PIDE/prover.scala	Sat Aug 07 19:58:38 2021 +0200
+++ b/src/Pure/PIDE/prover.scala	Sat Aug 07 21:25:47 2021 +0200
@@ -110,7 +110,7 @@
 
   private val process_result: Future[Process_Result] =
     Future.thread("process_result") {
-      val rc = process.join
+      val rc = process.join()
       val timing = process.get_timing
       Process_Result(rc, timing = timing)
     }