Fix rebase regression.

This branch did not pickup an important fix in master that assigns the
same timestamp ti all updates made within a transaction.

rust/template/differential_datalog/program.rs

@@ -1426,12 +1426,11 @@ impl Program {
                                             }
                                         }
                                     };
-                                    epoch += 1;
-                                    //print!("epoch: {}\n", epoch);
-                                    Self::advance(&mut sessions, &mut traces, epoch);
                                 },
                                 Ok(Msg::Flush) => {
                                     //println!("flushing");
+                                    epoch += 1;
+                                    Self::advance(&mut sessions, &mut traces, epoch);
                                     Self::flush(&mut sessions, &probe, worker, &peers, &frontier_ts, &progress_barrier);
                                     //println!("flushed");
                                     reply_send.send(Reply::FlushAck).map_err(|e| format!("failed to send ACK: {}", e))?;

test/datalog_tests/simple2.log.expected

@@ -7,18 +7,16 @@
 2: insert: (3.5, 1, 4.5)
 2: insert: (3.5, 2, 5.5)
 2: insert: (3.5, 3.5, 7)
-3: insert: x=1, total=1
-4: delete: x=1, total=1
-4: insert: x=1, total=3
-7: insert: y=2
-8: insert: y=3
-10: insert: y=5
-12: delete: y=2
-16: insert: x=1 y=1
-16: delete: x=1 y=1
-17: insert: x=2 y=2
-17: delete: x=2 y=2
-18: insert: x=3 y=3
-18: delete: x=3 y=3
-19: insert: x=4 y=4
-20: insert: x=2 y=2
+3: insert: x=1, total=3
+4: insert: y=2
+4: insert: y=3
+4: insert: y=5
+5: delete: y=2
+7: insert: x=4 y=4
+7: insert: x=1 y=1
+7: delete: x=1 y=1
+7: insert: x=3 y=3
+7: delete: x=3 y=3
+7: insert: x=2 y=2
+7: delete: x=2 y=2
+8: insert: x=2 y=2