fix: trash no-op addition messages

This partially restores the fix from c9cf2b7f2e
that was removed during the addition of new group consistency at de63527d94
but only for "Member added" messages.

Multiple "Member added" messages happen
when the same QR code is processed multiple times
by multiple devices.

src/chat.rs

@@ -5301,8 +5301,8 @@ mod tests {
         // Bob receives the add and deletion messages out of order
         let bob = TestContext::new_bob().await;
         bob.recv_msg(&add1).await;
-        bob.recv_msg(&add3).await;
-        let bob_chat_id = bob.recv_msg(&add2).await.chat_id;
+        let bob_chat_id = bob.recv_msg(&add3).await.chat_id;
+        bob.recv_msg_trash(&add2).await; // No-op addition message is trashed.
         assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?.len(), 4);
 
         bob.recv_msg(&remove2).await;

src/receive_imf.rs

@@ -1528,6 +1528,9 @@ async fn add_parts(
 
         let mut txt_raw = "".to_string();
         let (msg, typ): (&str, Viewtype) = if let Some(better_msg) = &better_msg {
+            if better_msg.is_empty() && is_partial_download.is_none() {
+                chat_id = DC_CHAT_ID_TRASH;
+            }
             (better_msg, Viewtype::Text)
         } else {
             (&part.msg, part.typ)
@@ -2197,7 +2200,8 @@ async fn update_chats_contacts_timestamps(
 /// Apply group member list, name, avatar and protection status changes from the MIME message.
 ///
 /// Returns `Vec` of group changes messages and, optionally, a better message to replace the
-/// original system message.
+/// original system message. If the better message is empty, the original system message
+/// should be trashed.
 ///
 /// * `to_ids` - contents of the `To` and `Cc` headers.
 /// * `past_ids` - contents of the `Chat-Group-Past-Members` header.
@@ -2394,7 +2398,12 @@ async fn apply_group_changes(
     }
 
     if let Some(added_id) = added_id {
-        added_ids.remove(&added_id);
+        if !added_ids.remove(&added_id) && !self_added {
+            // No-op "Member added" message.
+            //
+            // Trash it.
+            better_msg = Some(String::new());
+        }
     }
     if let Some(removed_id) = removed_id {
         removed_ids.remove(&removed_id);

src/receive_imf/tests.rs

@@ -5049,6 +5049,32 @@ async fn test_unarchive_on_member_removal() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_no_op_member_added_is_trash() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_chat_id = alice
+        .create_group_with_members(ProtectionStatus::Unprotected, "foos", &[bob])
+        .await;
+    send_text_msg(alice, alice_chat_id, "populate".to_string()).await?;
+    let msg = alice.pop_sent_msg().await;
+    bob.recv_msg(&msg).await;
+    let bob_chat_id = bob.get_last_msg().await.chat_id;
+    bob_chat_id.accept(bob).await?;
+
+    let fiona_id = Contact::create(alice, "", "fiona@example.net").await?;
+    add_contact_to_chat(alice, alice_chat_id, fiona_id).await?;
+    let msg = alice.pop_sent_msg().await;
+
+    let fiona_id = Contact::create(bob, "", "fiona@example.net").await?;
+    add_contact_to_chat(bob, bob_chat_id, fiona_id).await?;
+    bob.recv_msg_trash(&msg).await;
+    let contacts = get_chat_contacts(bob, bob_chat_id).await?;
+    assert_eq!(contacts.len(), 3);
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_forged_from() -> Result<()> {
     let mut tcm = TestContextManager::new();