test: Deletion request fails in an unencrypted chat and the message remains

src/chat/chat_tests.rs

@@ -3885,3 +3885,20 @@ async fn test_send_delete_request() -> Result<()> {
 
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_send_delete_request_no_encryption() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_chat = alice.create_email_chat(bob).await;
+
+    // Alice sends a message, then tries to send a deletion request which fails.
+    let sent1 = alice.send_text(alice_chat.id, "wtf").await;
+    assert!(message::delete_msgs_ex(alice, &[sent1.sender_msg_id], true)
+        .await
+        .is_err());
+    sent1.load_from_db().await;
+    assert_eq!(alice_chat.id.get_msg_cnt(alice).await?, 1);
+    Ok(())
+}

src/message.rs

@@ -1760,6 +1760,10 @@ pub async fn delete_msgs_ex(
         );
         if let Some(chat_id) = modified_chat_ids.iter().next() {
             let mut msg = Message::new_text("🚮".to_owned());
+            // We don't want to send deletion requests in chats w/o encryption:
+            // - These are usually chats with non-DC clients who won't respect deletion requests
+            //   anyway and display a weird trash bin message instead.
+            // - Deletion of world-visible unencrypted messages seems not very useful.
             msg.param.set_int(Param::GuaranteeE2ee, 1);
             msg.param
                 .set(Param::DeleteRequestFor, deleted_rfc724_mid.join(" "));

src/receive_imf.rs

@@ -1531,6 +1531,8 @@ async fn add_parts(
     } else if let Some(rfc724_mid_list) = mime_parser.get_header(HeaderDef::ChatDelete) {
         chat_id = DC_CHAT_ID_TRASH;
         if let Some(part) = mime_parser.parts.first() {
+            // See `message::delete_msgs_ex()`, unlike edit requests, DC doesn't send unencrypted
+            // deletion requests, so there's no need to support them.
             if part.param.get_bool(Param::GuaranteeE2ee).unwrap_or(false) {
                 let mut modified_chat_ids = HashSet::new();
                 let mut msg_ids = Vec::new();