Fix garbled replies to replies due to invalid reply formatting

src/domain/session/room/timeline/tiles/BaseMessageTile.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2020 Bruno Windels <bruno@windels.cloud>
+Copyright 2024 Mirian Margiani <mixosaurus+ichthyo@pm.me>
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -147,7 +148,7 @@ export class BaseMessageTile extends SimpleTile {
     }
 
     createReplyContent(msgtype, body) {
-        return this._entry.createReplyContent(msgtype, body);
+        return this._entry.createReplyContent(msgtype, body, this.permaLink);
     }
 
     redact(reason, log) {

src/matrix/room/timeline/entries/BaseEventEntry.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2021 The Matrix.org Foundation C.I.C.
+Copyright 2024 Mirian Margiani <mixosaurus+ichthyo@pm.me>
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -185,8 +186,8 @@ export class BaseEventEntry extends BaseEntry {
         return createAnnotation(this.id, key);
     }
 
-    createReplyContent(msgtype, body) {
-        return createReplyContent(this, msgtype, body);
+    createReplyContent(msgtype, body, permaLink) {
+        return createReplyContent(this, msgtype, body, permaLink);
     }
 
     /** takes both remote event id and local txn id into account, see overriding in PendingEventEntry */

src/matrix/room/timeline/entries/reply.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2021 The Matrix.org Foundation C.I.C.
+Copyright 2024 Mirian Margiani <mixosaurus+ichthyo@pm.me>
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -36,7 +37,42 @@ function fallbackPrefix(msgtype) {
     return msgtype === "m.emote" ? "* " : "";
 }
 
-function _createReplyContent(targetId, msgtype, body, formattedBody) {
+function _parsePlainBody(plainBody) {
+    // Strip any existing reply fallback and return an array of lines.
+
+    const bodyLines = plainBody.trim().split("\n");
+
+    return bodyLines
+        .map((elem, index, array) => {
+            if (index > 0 && array[index-1][0] !== '>') {
+                // stop stripping the fallback at the first line of non-fallback text
+                return elem;
+            } else if (elem[0] === '>' && elem[1] === ' ') {
+                return null;
+            } else {
+                return elem;
+            }
+        })
+        .filter((elem) => elem !== null)
+        // Join, trim, and split to remove any line breaks that were left between the
+        // fallback and the actual message body. Don't use trim() because that would
+        // also remove any other whitespace at the beginning of the message that the
+        // user added intentionally.
+        .join('\n')
+        .replace(/^\n+|\n+$/g, '')
+        .split('\n')
+}
+
+function _parseFormattedBody(formattedBody) {
+    // Strip any existing reply fallback and return a HTML string again.
+
+    // This is greedy and definitely not the most efficient way to do it.
+    // However, this function is only called when sending a reply (so: not too
+    // often) and it should make sure that all instances of <mx-reply> are gone.
+    return formattedBody.replace(/<mx-reply>[\s\S]*<\/mx-reply>/gi, '');
+}
+
+function _createReplyContent(targetId, targetSenderId, msgtype, body, formattedBody) {
     return {
         msgtype,
         body,
@@ -46,29 +82,54 @@ function _createReplyContent(targetId, msgtype, body, formattedBody) {
             "m.in_reply_to": {
                 "event_id": targetId
             }
+        },
+        "m.mentions": {
+            "user_ids": [
+                targetSenderId,
+            ]
         }
     };
 }
 
-export function createReplyContent(entry, msgtype, body) {
-    // TODO check for absense of sender / body / msgtype / etc?
+export function createReplyContent(entry, msgtype, body, permaLink) {
+    // NOTE We assume sender, body, and msgtype are never invalid because they
+    //      are required fields.
     const nonTextual = fallbackForNonTextualMessage(entry.content.msgtype);
     const prefix = fallbackPrefix(entry.content.msgtype);
     const sender = entry.sender;
-    const name = entry.displayName || sender;
+    const repliedToId = entry.id;
 
-    const formattedBody = nonTextual || entry.content.formatted_body ||
-        (entry.content.body && htmlEscape(entry.content.body)) || "";
-    const formattedFallback = `<mx-reply><blockquote>In reply to ${prefix}` +
-        `<a href="https://matrix.to/#/${sender}">${name}</a><br />` +
-        `${formattedBody}</blockquote></mx-reply>`;
+    // TODO collect user mentions (sender and any previous mentions)
+    // Considerations:
+    // - Who should be included in the mentions? In a reply chain, should all
+    //   previous mentions be carried over indefinitely? How to decide when to
+    //   stop carrying mentions?
+    // - Don't add a mentions section when replying to own messages without
+    //   any other mentions. As per https://spec.matrix.org/v1.12/client-server-api/#user-and-room-mentions
+    //       "Users should not add their own Matrix ID to the m.mentions property
+    //        as outgoing messages cannot self-notify."
 
+    // Generate new plain body with plain reply fallback
     const plainBody = nonTextual || entry.content.body || "";
-    const bodyLines = plainBody.split("\n");
+    const bodyLines = _parsePlainBody(plainBody);
     bodyLines[0] = `> ${prefix}<${sender}> ${bodyLines[0]}`
     const plainFallback = bodyLines.join("\n> ");
-
     const newBody = plainFallback + '\n\n' + body;
-    const newFormattedBody = formattedFallback + htmlEscape(body);
-    return _createReplyContent(entry.id, msgtype, newBody, newFormattedBody);
+
+    // Generate new formatted body with formatted reply fallback
+    const formattedBody = nonTextual || entry.content.formatted_body ||
+        (entry.content.body && htmlEscape(entry.content.body)) || "";
+    const cleanedFormattedBody = _parseFormattedBody(formattedBody);
+    const formattedFallback =
+        `<mx-reply>` +
+            `<blockquote>` +
+                `<a href="${permaLink}">In reply to</a>` +
+                `${prefix}<a href="https://matrix.to/#/${sender}">${sender}</a>` +
+                `<br />` +
+                `${cleanedFormattedBody}` +
+            `</blockquote>` +
+        `</mx-reply>`;
+    const newFormattedBody = formattedFallback + htmlEscape(body).replaceAll('\n', '<br/>');
+
+    return _createReplyContent(repliedToId, sender, msgtype, newBody, newFormattedBody);
 }