msglist: update message counter upon filter change

Update message counter in msglist when the filter is changed (either set or
cleared in the msgstore).

When we apply a filter, we change the number of uids in the message
store. This can unintentionally trigger the storeUpdate() function of
the msglist which checks the number of uids for new messages and
advances the pointer by the difference in the number of messages. This
can be avoided when we update the message counter upon changing the
filter.

Fixes: https://todo.sr.ht/~rjarry/aerc/23
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

lib/msgstore.go

@@ -43,6 +43,7 @@ type MessageStore struct {
 
 	// Map of uids we've asked the worker to fetch
 	onUpdate       func(store *MessageStore) // TODO: multiple onUpdate handlers
+	onFilterChange func(store *MessageStore)
 	onUpdateDirs   func()
 	pendingBodies  map[uint32]interface{}
 	pendingHeaders map[uint32]interface{}
@@ -323,6 +324,10 @@ func (store *MessageStore) OnUpdate(fn func(store *MessageStore)) {
 	store.onUpdate = fn
 }
 
+func (store *MessageStore) OnFilterChange(fn func(store *MessageStore)) {
+	store.onFilterChange = fn
+}
+
 func (store *MessageStore) OnUpdateDirs(fn func()) {
 	store.onUpdateDirs = fn
 }
@@ -655,6 +660,9 @@ func (store *MessageStore) ApplyFilter(results []uint32) {
 	store.results = nil
 	store.filtered = results
 	store.filter = true
+	if store.onFilterChange != nil {
+		store.onFilterChange(store)
+	}
 	store.update()
 	// any marking is now invalid
 	// TODO: could save that probably
@@ -668,6 +676,9 @@ func (store *MessageStore) ApplyClear() {
 	if store.BuildThreads() {
 		store.runThreadBuilder()
 	}
+	if store.onFilterChange != nil {
+		store.onFilterChange(store)
+	}
 }
 
 func (store *MessageStore) nextPrevResult(delta int) {

widgets/msglist.go

@@ -367,6 +367,12 @@ func (ml *MessageList) SetStore(store *lib.MessageStore) {
 		ml.spinner.Stop()
 		ml.nmsgs = len(store.Uids())
 		store.OnUpdate(ml.storeUpdate)
+		store.OnFilterChange(func(store *lib.MessageStore) {
+			if ml.Store() != store {
+				return
+			}
+			ml.nmsgs = len(store.Uids())
+		})
 	} else {
 		ml.spinner.Start()
 	}