events: Improve compatibility of generated and stripped plain reply fallback

crates/ruma-common/CHANGELOG.md

@@ -46,6 +46,8 @@ Improvements:
 - Stabilize support for annotations and reactions (MSC2677 / Matrix 1.7)
 - Add support for intentional mentions push rules (MSC3952 / Matrix 1.7)
 - Stabilize support for VoIP signalling improvements (MSC2746 / Matrix 1.7)
+- Make the generated and stripped plain text reply fallback behavior more compatible with most
+  of the Matrix ecosystem.
 
 # 0.11.3
 

crates/ruma-common/src/events/room/message/reply.rs

@@ -113,7 +113,7 @@ pub fn plain_and_formatted_reply_body(
 ) -> (String, String) {
     let (quoted, quoted_html) = get_message_quote_fallbacks(original_message);
 
-    let plain = format!("{quoted}\n{body}");
+    let plain = format!("{quoted}\n\n{body}");
     let html = match formatted {
         Some(formatted) => format!("{quoted_html}{formatted}"),
         None => format!("{quoted_html}{}", EscapeHtmlEntities(body)),

crates/ruma-common/src/events/room/message/sanitize.rs

@@ -71,6 +71,10 @@ pub fn remove_html_reply_fallback(s: &str) -> String {
 ///
 /// [rich reply fallback]: https://spec.matrix.org/latest/client-server-api/#fallbacks-for-rich-replies
 pub fn remove_plain_reply_fallback(mut s: &str) -> &str {
+    if !s.starts_with("> ") {
+        return s;
+    }
+
     while s.starts_with("> ") {
         if let Some((_line, rest)) = s.split_once('\n') {
             s = rest;
@@ -79,7 +83,12 @@ pub fn remove_plain_reply_fallback(mut s: &str) -> &str {
         }
     }
 
-    s
+    // Strip the first line after the fallback if it is empty.
+    if let Some(rest) = s.strip_prefix('\n') {
+        rest
+    } else {
+        s
+    }
 }
 
 #[cfg(test)]
@@ -194,16 +203,18 @@ mod tests {
             remove_plain_reply_fallback(
                 "> <@user:notareal.hs> Replied to on\n\
                  > two lines\n\
+                 \n\
+                 \n\
                  This is my reply"
             ),
-            "This is my reply"
+            "\nThis is my reply"
         );
 
         assert_eq!(remove_plain_reply_fallback("\n> Not on first line"), "\n> Not on first line");
 
         assert_eq!(
             remove_plain_reply_fallback("> <@user:notareal.hs> Previous message\n\n> New quote"),
-            "\n> New quote"
+            "> New quote"
         );
     }
 }

crates/ruma-common/tests/events/room_message.rs

@@ -282,6 +282,7 @@ fn escape_tags_in_plain_reply_body() {
         body,
         "\
         > <@user:example.org> Usage: cp <source> <destination>\n\
+        \n\
         Usage: rm <path>\
         "
     );
@@ -352,6 +353,7 @@ fn reply_sanitize() {
         body,
         "\
         > <@user:example.org> # This is the first message\n\
+        \n\
         This is the _second_ message\
         "
     );
@@ -379,6 +381,7 @@ fn reply_sanitize() {
         body,
         "\
         > <@user:example.org> This is the _second_ message\n\
+        \n\
         This is **my** reply\
         "
     );
@@ -448,6 +451,7 @@ fn make_replacement_with_reply() {
         body,
         "\
         > <@user:example.org> # This is the first message\n\
+        \n\
         * This is _an edited_ reply.\
         "
     );