Make sure we have a correct next first after expiring on startup

Signed-off-by: Derek Collison <derek@nats.io>

server/filestore.go

@@ -1311,6 +1311,7 @@ func (fs *fileStore) expireMsgsOnRecover() {
 		}
 
 		var smv StoreMsg
+		var needNextFirst bool
 
 		// Walk messages and remove if expired.
 		mb.ensurePerSubjectInfoLoaded()
@@ -1325,14 +1326,13 @@ func (fs *fileStore) expireMsgsOnRecover() {
 						mb.dmap = nil
 					}
 				}
-				// Keep this update just in case since we are removing dmap entries.
-				mb.first.seq = seq
+				// Keep this updated just in case since we are removing dmap entries.
+				mb.first.seq, needNextFirst = seq, true
 				continue
 			}
 			// Break on other errors.
 			if err != nil || sm == nil {
-				// Keep this update just in case since we could have removed dmap entries.
-				mb.first.seq = seq
+				mb.first.seq, needNextFirst = seq, true
 				break
 			}
 
@@ -1340,6 +1340,7 @@ func (fs *fileStore) expireMsgsOnRecover() {
 
 			// Check for done.
 			if minAge < sm.ts {
+				mb.first.seq, needNextFirst = sm.seq, false
 				mb.first.seq = sm.seq
 				mb.first.ts = sm.ts
 				nts = sm.ts
@@ -1348,6 +1349,7 @@ func (fs *fileStore) expireMsgsOnRecover() {
 
 			// Delete the message here.
 			if mb.msgs > 0 {
+				mb.first.seq, needNextFirst = seq, true
 				sz := fileStoreMsgSize(sm.subj, sm.hdr, sm.msg)
 				mb.bytes -= sz
 				bytes += sz
@@ -1359,7 +1361,10 @@ func (fs *fileStore) expireMsgsOnRecover() {
 			mb.removeSeqPerSubject(sm.subj, seq, nil)
 			fs.removePerSubject(sm.subj)
 		}
-
+		// Make sure we have a proper next first sequence.
+		if needNextFirst {
+			mb.selectNextFirst()
+		}
 		// Check if empty after processing, could happen if tail of messages are all deleted.
 		needWriteIndex := true
 		if mb.msgs == 0 {
@@ -2365,7 +2370,7 @@ func (fs *fileStore) StoreMsg(subj string, hdr, msg []byte) (uint64, int64, erro
 
 // skipMsg will update this message block for a skipped message.
 // If we do not have any messages, just update the metadata, otherwise
-// we will place and empty record marking the sequence as used. The
+// we will place an empty record marking the sequence as used. The
 // sequence will be marked erased.
 // fs lock should be held.
 func (mb *msgBlock) skipMsg(seq uint64, now time.Time) {