feat: Set mime_modified for the last message part, not the first (#4462)

Otherwise the "Show Full Message..." button appears somewhere in the middle of the multipart
message, e.g. after a text in the first message bubble, but before a text in the second
bubble. Moreover, if the second/n-th bubble's text is shortened (ends with "[...]"), the user should
scroll up to click on "Show Full Message..." which doesn't look reasonable. Scrolling down looks
more acceptable (e.g. if the first bubble's text is shortened in a multipart message).

I'd even suggest to show somehow that message bubbles belong to the same multipart message, e.g. add
"[↵]" to the text of all bubbles except the last one, but let's discuss this first.

Author: iequidoo

src/mimeparser.rs

@@ -105,14 +105,12 @@ pub(crate) struct MimeMessage {
     /// received.
     pub(crate) footer: Option<String>,
 
-    // if this flag is set, the parts/text/etc. are just close to the original mime-message;
-    // clients should offer a way to view the original message in this case
+    /// If set, this is a modified MIME message; clients should offer a way to view the original
+    /// MIME message in this case.
     pub is_mime_modified: bool,
 
-    /// The decrypted, raw mime structure.
-    ///
-    /// This is non-empty iff `is_mime_modified` and the message was actually encrypted. It is used
-    /// for e.g. late-parsing HTML.
+    /// Decrypted, raw MIME structure. Nonempty iff `is_mime_modified` and the message was actually
+    /// encrypted.
     pub decoded_data: Vec<u8>,
 
     /// Hop info for debugging.

src/receive_imf.rs

@@ -1406,10 +1406,11 @@ async fn add_parts(
     // we save the full mime-message and add a flag
     // that the ui should show button to display the full message.
 
-    // a flag used to avoid adding "show full message" button to multiple parts of the message.
-    let mut save_mime_modified = mime_parser.is_mime_modified;
+    // We add "Show Full Message" button to the last message bubble (part) if this flag evaluates to
+    // `true` finally.
+    let mut save_mime_modified = false;
 
-    let mime_headers = if save_mime_headers || save_mime_modified {
+    let mime_headers = if save_mime_headers || mime_parser.is_mime_modified {
         let headers = if !mime_parser.decoded_data.is_empty() {
             mime_parser.decoded_data.clone()
         } else {
@@ -1475,7 +1476,8 @@ async fn add_parts(
         }
     }
 
-    for part in &mime_parser.parts {
+    let mut parts = mime_parser.parts.iter().peekable();
+    while let Some(part) = parts.next() {
         if part.is_reaction {
             let reaction_str = simplify::remove_footers(part.msg.as_str());
             let is_incoming_fresh = mime_parser.incoming && !seen && !fetching_existing_messages;
@@ -1519,14 +1521,11 @@ async fn add_parts(
         } else {
             (&part.msg, part.typ)
         };
-
         let part_is_empty =
             typ == Viewtype::Text && msg.is_empty() && part.param.get(Param::Quote).is_none();
-        let mime_modified = save_mime_modified && !part_is_empty;
-        if mime_modified {
-            // Avoid setting mime_modified for more than one part.
-            save_mime_modified = false;
-        }
+
+        save_mime_modified |= mime_parser.is_mime_modified && !part_is_empty && !hidden;
+        let save_mime_modified = save_mime_modified && parts.peek().is_none();
 
         if part.typ == Viewtype::Text {
             let msg_raw = part.msg_raw.as_ref().cloned().unwrap_or_default();
@@ -1546,8 +1545,7 @@ 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() || (is_location_kml && msg.is_empty() && typ == Viewtype::Text);
+        let trash = chat_id.is_trash() || (is_location_kml && part_is_empty && !save_mime_modified);
 
         let row_id = context
             .sql
@@ -1610,14 +1608,14 @@ RETURNING id
                     },
                     hidden,
                     part.bytes as isize,
-                    if (save_mime_headers || mime_modified) && !trash {
+                    if (save_mime_headers || save_mime_modified) && !trash {
                         mime_headers.clone()
                     } else {
                         Vec::new()
                     },
                     mime_in_reply_to,
                     mime_references,
-                    mime_modified,
+                    save_mime_modified,
                     part.error.as_deref().unwrap_or_default(),
                     ephemeral_timer,
                     ephemeral_timestamp,