Trash messages more thoroughly (#2273)

Esp. remove some information for newly-arriving messages

src/dc_receive_imf.rs

@@ -954,26 +954,34 @@ async fn add_parts(
                     }
                 };
 
+                // If you change which information is skipped if the message is trashed,
+                // also change `MsgId::trash()` and `delete_expired_messages()`
+                let trash = chat_id.is_trash();
+
                 stmt.execute(paramsv![
                     rfc724_mid,
                     server_folder,
                     server_uid as i32,
                     chat_id,
-                    from_id as i32,
+                    if trash { 0 } else { from_id as i32 },
-                    to_id as i32,
+                    if trash { 0 } else { to_id as i32 },
                     sort_timestamp,
                     sent_timestamp,
                     rcvd_timestamp,
                     part.typ,
                     state,
                     is_dc_message,
-                    part.msg,
+                    if trash { "" } else { &part.msg },
                     // txt_raw might contain invalid utf8
-                    txt_raw,
+                    if trash { "" } else { &txt_raw },
-                    part.param.to_string(),
+                    if trash {
+                        "".to_string()
+                    } else {
+                        part.param.to_string()
+                    },
                     part.bytes as isize,
                     is_hidden,
-                    if save_mime_headers || mime_modified {
+                    if (save_mime_headers || mime_modified) && !trash {
                         mime_headers.clone()
                     } else {
                         None

src/ephemeral.rs

@@ -308,8 +308,10 @@ pub(crate) async fn delete_expired_messages(context: &Context) -> Result<bool, E
     let mut updated = context
         .sql
         .execute(
+            // If you change which information is removed here, also change MsgId::trash() and
+            // which information dc_receive_imf::add_parts() still adds to the db if the chat_id is TRASH
             "UPDATE msgs \
-             SET chat_id=?, txt='', txt_raw='', from_id=0, to_id=0, param='' \
+             SET chat_id=?, txt='', txt_raw='', mime_headers='', from_id=0, to_id=0, param='' \
              WHERE \
              ephemeral_timestamp != 0 \
              AND ephemeral_timestamp <= ? \

src/message.rs

@@ -147,13 +147,17 @@ impl MsgId {
 
     /// Put message into trash chat and delete message text.
     ///
-    /// It means the message is deleted locally, but not on the server
+    /// It means the message is deleted locally, but not on the server.
-    /// yet.
+    /// We keep some infos to
+    /// 1. not download the same message again
+    /// 2. be able to delete the message on the server if we want to
     pub async fn trash(self, context: &Context) -> crate::sql::Result<()> {
         let chat_id = ChatId::new(DC_CHAT_ID_TRASH);
         context
             .sql
             .execute(
+                // If you change which information is removed here, also change delete_expired_messages() and
+                // which information dc_receive_imf::add_parts() still adds to the db if the chat_id is TRASH
                 "UPDATE msgs SET chat_id=?, txt='', txt_raw='', mime_headers='', from_id=0, to_id=0, param='' WHERE id=?",
                 paramsv![chat_id, self],
             )