fix: Only add "member added/removed" messages if they actually do that (#5992)

There were many cases in which "member added/removed" messages were added to chats even if they
actually do nothing because a member is already added or removed. But primarily this fixes a
scenario when Alice has several devices and shares an invite link somewhere, and both their devices
handle the SecureJoin and issue `ChatGroupMemberAdded` messages so all other members see a
duplicated group member addition.

src/chat.rs

@@ -5371,7 +5371,7 @@ mod tests {
 
         // Eventually, first removal message arrives.
         // This has no effect.
-        bob.recv_msg(&remove1).await;
+        bob.recv_msg_trash(&remove1).await;
         assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?.len(), 2);
         Ok(())
     }

src/receive_imf.rs

@@ -1423,7 +1423,11 @@ async fn add_parts(
     if let Some(msg) = group_changes_msgs.1 {
         match &better_msg {
             None => better_msg = Some(msg),
-            Some(_) => group_changes_msgs.0.push(msg),
+            Some(_) => {
+                if !msg.is_empty() {
+                    group_changes_msgs.0.push(msg)
+                }
+            }
         }
     }
 
@@ -1506,6 +1510,9 @@ 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)
@@ -2077,8 +2084,11 @@ async fn create_group(
 
 /// Apply group member list, name, avatar and protection status changes from the MIME message.
 ///
-/// Optionally returns better message to replace the original system message.
-/// is_partial_download: whether the message is not fully downloaded.
+/// Returns `Vec` of group changes messages and, optionally, a better message to replace the
+/// original system message. If the better message is empty, the original system message should be
+/// just omitted.
+///
+/// * `is_partial_download` - whether the message is not fully downloaded.
 #[allow(clippy::too_many_arguments)]
 async fn apply_group_changes(
     context: &Context,
@@ -2180,39 +2190,47 @@ async fn apply_group_changes(
 
     if let Some(removed_addr) = mime_parser.get_header(HeaderDef::ChatGroupMemberRemoved) {
         removed_id = Contact::lookup_id_by_addr(context, removed_addr, Origin::Unknown).await?;
-
-        better_msg = if removed_id == Some(from_id) {
-            Some(stock_str::msg_group_left_local(context, from_id).await)
-        } else {
-            Some(stock_str::msg_del_member_local(context, removed_addr, from_id).await)
-        };
-
-        if removed_id.is_some() {
-            if !allow_member_list_changes {
-                info!(
-                    context,
-                    "Ignoring removal of {removed_addr:?} from {chat_id}."
-                );
+        if let Some(id) = removed_id {
+            if allow_member_list_changes && chat_contacts.contains(&id) {
+                better_msg = if id == from_id {
+                    Some(stock_str::msg_group_left_local(context, from_id).await)
+                } else {
+                    Some(stock_str::msg_del_member_local(context, removed_addr, from_id).await)
+                };
             }
         } else {
             warn!(context, "Removed {removed_addr:?} has no contact id.")
         }
+        better_msg.get_or_insert_with(Default::default);
+        if !allow_member_list_changes {
+            info!(
+                context,
+                "Ignoring removal of {removed_addr:?} from {chat_id}."
+            );
+        }
     } else if let Some(added_addr) = mime_parser.get_header(HeaderDef::ChatGroupMemberAdded) {
-        better_msg = Some(stock_str::msg_add_member_local(context, added_addr, from_id).await);
-
         if allow_member_list_changes {
-            if !recreate_member_list {
-                if let Some(contact_id) =
-                    Contact::lookup_id_by_addr(context, added_addr, Origin::Unknown).await?
-                {
+            let is_new_member;
+            if let Some(contact_id) =
+                Contact::lookup_id_by_addr(context, added_addr, Origin::Unknown).await?
+            {
+                if !recreate_member_list {
                     added_id = Some(contact_id);
-                } else {
-                    warn!(context, "Added {added_addr:?} has no contact id.")
                 }
+                is_new_member = !chat_contacts.contains(&contact_id);
+            } else {
+                warn!(context, "Added {added_addr:?} has no contact id.");
+                is_new_member = false;
+            }
+
+            if is_new_member || self_added {
+                better_msg =
+                    Some(stock_str::msg_add_member_local(context, added_addr, from_id).await);
             }
         } else {
             info!(context, "Ignoring addition of {added_addr:?} to {chat_id}.");
         }
+        better_msg.get_or_insert_with(Default::default);
     } else if let Some(old_name) = mime_parser
         .get_header(HeaderDef::ChatGroupNameChanged)
         .map(|s| s.trim())

src/receive_imf/tests.rs

@@ -4185,9 +4185,8 @@ async fn test_recreate_contact_list_on_missing_message() -> Result<()> {
     // readd fiona
     add_contact_to_chat(&alice, chat_id, alice_fiona).await?;
 
-    alice.recv_msg(&remove_msg).await;
-
     // delayed removal of fiona shouldn't remove her
+    alice.recv_msg_trash(&remove_msg).await;
     assert_eq!(get_chat_contacts(&alice, chat_id).await?.len(), 4);
 
     Ok(())
@@ -4947,6 +4946,32 @@ 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();