Send MailboxUpdate events when threads are updated

Depending on the insertion order of folders which is non-deterministic
because it relies on the kernel's scheduling of parsing threads, the
listing the user sees might not be up-to-date because later thread
updates are never broadcast. This results in inconsistencies between
threads and mail listings when a thread's root envelope was part of a
not broadcast update leading to `key not found` panics in a listing's
hashmaps.

melib/src/collection.rs

@@ -120,13 +120,15 @@ impl Collection {
         }
     }
 
+    /// Merge new Mailbox to collection and update threads.
+    /// Returns a list of already existing folders whose threads were updated
     pub fn merge(
         &mut self,
         mut envelopes: FnvHashMap<EnvelopeHash, Envelope>,
         folder_hash: FolderHash,
         mailbox: &mut Mailbox,
         sent_folder: Option<FolderHash>,
-    ) {
+    ) -> Option<StackVec<FolderHash>> {
         self.sent_folder = sent_folder;
         envelopes.retain(|&h, e| {
             if self.message_ids.contains_key(e.message_id().raw()) {
@@ -150,6 +152,8 @@ impl Collection {
             ref sent_folder,
             ..
         } = self;
+
+        let mut ret = StackVec::new();
         for (t_fh, t) in threads.iter_mut() {
             if sent_folder.map(|f| f == folder_hash).unwrap_or(false) {
                 let mut ordered_hash_set = new_threads
@@ -163,8 +167,12 @@ impl Collection {
                         .partial_cmp(&envelopes[b].date())
                         .unwrap()
                 });
+                let mut updated = false;
                 for h in ordered_hash_set {
-                    t.insert_reply(envelopes, h);
+                    updated |= t.insert_reply(envelopes, h);
+                }
+                if updated {
+                    ret.push(*t_fh);
                 }
                 continue;
             }
@@ -183,6 +191,11 @@ impl Collection {
             }
         }
         threads.insert(folder_hash, new_threads);
+        if ret.is_empty() {
+            None
+        } else {
+            Some(ret)
+        }
     }
 
     pub fn update(&mut self, old_hash: EnvelopeHash, envelope: Envelope, folder_hash: FolderHash) {

ui/src/conf/accounts.rs

@@ -468,8 +468,14 @@ impl Account {
             return;
         }
         let (envelopes, mut mailbox) = payload.unwrap();
-        self.collection
-            .merge(envelopes, folder_hash, &mut mailbox, self.sent_folder);
+        if let Some(updated_folders) =
+            self.collection
+                .merge(envelopes, folder_hash, &mut mailbox, self.sent_folder)
+        {
+            for f in updated_folders {
+                self.notify_fn.notify(f);
+            }
+        }
         self.folders
             .insert(folder_hash, MailboxEntry::Available(mailbox));
     }