[FIXED] Expire on recover could not update global per subject map (#4439)

When expiring complete blocks on recover make sure to update global
subject index psim.

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

server/filestore.go

@@ -1315,6 +1315,11 @@ func (fs *fileStore) expireMsgsOnRecover() {
 			fs.psim = make(map[string]*psi)
 			return false
 		}
+		// Make sure we do subject cleanup as well.
+		mb.ensurePerSubjectInfoLoaded()
+		for subj := range mb.fss {
+			fs.removePerSubject(subj)
+		}
 		mb.dirtyCloseWithRemove(true)
 		deleted++
 		return true

server/filestore_test.go

@@ -4662,6 +4662,40 @@ func TestFileStoreFSSCloseAndKeepOnExpireOnRecoverBug(t *testing.T) {
 	})
 }
 
+func TestFileStoreExpireOnRecoverSubjectAccounting(t *testing.T) {
+	const msgLen = 19
+	msg := bytes.Repeat([]byte("A"), msgLen)
+
+	testFileStoreAllPermutations(t, func(t *testing.T, fcfg FileStoreConfig) {
+		fcfg.BlockSize = 100
+		ttl := 200 * time.Millisecond
+		scfg := StreamConfig{Name: "zzz", Subjects: []string{"*"}, Storage: FileStorage, MaxAge: ttl}
+
+		fs, err := newFileStore(fcfg, scfg)
+		require_NoError(t, err)
+		defer fs.Stop()
+
+		// These are in first block.
+		fs.StoreMsg("A", nil, msg)
+		fs.StoreMsg("B", nil, msg)
+		time.Sleep(ttl / 2)
+		// This one in 2nd block.
+		fs.StoreMsg("C", nil, msg)
+		fs.Stop()
+
+		time.Sleep(ttl/2 + 10*time.Millisecond)
+
+		fs, err = newFileStore(fcfg, scfg)
+		require_NoError(t, err)
+		defer fs.Stop()
+
+		// Make sure we take into account PSIM when throwing a whole block away.
+		if state := fs.State(); state.NumSubjects != 1 {
+			t.Fatalf("Expected 1 subject, got %d", state.NumSubjects)
+		}
+	})
+}
+
 func TestFileStoreFSSBadStateBug(t *testing.T) {
 	testFileStoreAllPermutations(t, func(t *testing.T, fcfg FileStoreConfig) {
 		fs, err := newFileStore(