Strip direction override characters from display names (#1992)

Strip RLO and LRO characters from name and rawDisplayName so they
can safely be embedded into other text without messing up the text
ordering.

Fixes element-hq/element-web#1712

src/models/room-member.ts

@@ -131,7 +131,9 @@ export class RoomMember extends EventEmitter {
             this.disambiguate,
         );
 
-        this.rawDisplayName = event.getDirectionalContent().displayname;
+        // not quite raw: we strip direction override chars so it can safely be inserted into
+        // blocks of text without breaking the text direction
+        this.rawDisplayName = utils.removeDirectionOverrideChars(event.getDirectionalContent().displayname);
         if (!this.rawDisplayName || !utils.removeHiddenChars(this.rawDisplayName)) {
             this.rawDisplayName = this.userId;
         }
@@ -355,15 +357,26 @@ function calculateDisplayName(
     roomState: RoomState,
     disambiguate: boolean,
 ): string {
-    if (disambiguate) return displayName + " (" + selfUserId + ")";
+    if (disambiguate) return utils.removeDirectionOverrideChars(displayName) + " (" + selfUserId + ")";
 
     if (!displayName || displayName === selfUserId) return selfUserId;
 
     // First check if the displayname is something we consider truthy
     // after stripping it of zero width characters and padding spaces
     if (!utils.removeHiddenChars(displayName)) return selfUserId;
 
-    return displayName;
+    // We always strip the direction override characters (LRO and RLO).
+    // These override the text direction for all subsequent characters
+    // in the paragraph so if display names contained these, they'd
+    // need to be wrapped in something to prevent this from leaking out
+    // (which we can do in HTML but not text) or we'd need to add
+    // control characters to the string to reset any overrides (eg.
+    // adding PDF characters at the end). As far as we can see,
+    // there should be no reason these would be necessary - rtl display
+    // names should flip into the correct direction automatically based on
+    // the characters, and you can still embed rtl in ltr or vice versa
+    // with the embed chars or marker chars.
+    return utils.removeDirectionOverrideChars(displayName);
 }
 
 /**

src/utils.ts

@@ -387,6 +387,18 @@ export function removeHiddenChars(str: string): string {
     return "";
 }
 
+/**
+ * Removes the direction override characters from a string
+ * @param {string} input
+ * @returns string with chars removed
+ */
+export function removeDirectionOverrideChars(str: string): string {
+    if (typeof str === "string") {
+        return str.replace(/[\u202d-\u202e]/g, '');
+    }
+    return "";
+}
+
 export function normalize(str: string): string {
     // Note: we have to match the filter with the removeHiddenChars() because the
     // function strips spaces and other characters (M becomes RN for example, in lowercase).