Implement reply chain fallback for threads backwards compatibility

src/components/structures/ThreadView.tsx

@@ -55,6 +55,7 @@ interface IProps {
 }
 interface IState {
     thread?: Thread;
+    lastThreadReply?: MatrixEvent;
     layout: Layout;
     editState?: EditorStateTransfer;
     replyToEvent?: MatrixEvent;
@@ -142,14 +143,14 @@ export default class ThreadView extends React.Component<IProps, IState> {
         if (!thread) {
             thread = this.props.room.createThread([mxEv]);
         }
-        thread.on(ThreadEvent.Update, this.updateThread);
+        thread.on(ThreadEvent.Update, this.updateLastThreadReply);
         thread.once(ThreadEvent.Ready, this.updateThread);
         this.updateThread(thread);
     };
 
     private teardownThread = () => {
         if (this.state.thread) {
-            this.state.thread.removeListener(ThreadEvent.Update, this.updateThread);
+            this.state.thread.removeListener(ThreadEvent.Update, this.updateLastThreadReply);
             this.state.thread.removeListener(ThreadEvent.Ready, this.updateThread);
         }
     };
@@ -165,13 +166,22 @@ export default class ThreadView extends React.Component<IProps, IState> {
         if (thread && this.state.thread !== thread) {
             this.setState({
                 thread,
+                lastThreadReply: thread.lastReply,
             }, () => {
                 thread.emit(ThreadEvent.ViewThread);
                 this.timelinePanelRef.current?.refreshTimeline();
             });
         }
     };
 
+    private updateLastThreadReply = () => {
+        if (this.state.thread) {
+            this.setState({
+                lastThreadReply: this.state.thread.lastReply,
+            });
+        }
+    };
+
     private onScroll = (): void => {
         if (this.props.initialEvent && this.props.isInitialEventHighlighted) {
             dis.dispatch({
@@ -199,8 +209,12 @@ export default class ThreadView extends React.Component<IProps, IState> {
             : null;
 
         const threadRelation: IEventRelation = {
-            rel_type: RelationType.Thread,
-            event_id: this.state.thread?.id,
+            "rel_type": RelationType.Thread,
+            "event_id": this.state.thread?.id,
+            "m.in_reply_to": {
+                "event_id": this.state.lastThreadReply?.getId(),
+                "m.render_in": ["m.room"],
+            },
         };
 
         const messagePanelClassNames = classNames(

src/components/views/elements/ReplyChain.tsx

@@ -17,7 +17,7 @@ limitations under the License.
 
 import React from 'react';
 import classNames from 'classnames';
-import { MatrixEvent } from 'matrix-js-sdk/src/models/event';
+import { IEventRelation, MatrixEvent } from 'matrix-js-sdk/src/models/event';
 import escapeHtml from "escape-html";
 import sanitizeHtml from "sanitize-html";
 import { Room } from 'matrix-js-sdk/src/models/room';
@@ -111,10 +111,8 @@ export default class ReplyChain extends React.Component<IProps, IState> {
         // can't just rely on ev.getContent() by itself because historically we
         // still show the reply from the original message even though the edit
         // event does not include the relation reply.
-        const mRelatesTo = ev.getContent()['m.relates_to'] || ev.getWireContent()['m.relates_to'];
-        if (mRelatesTo && mRelatesTo['m.in_reply_to']) {
-            const mInReplyTo = mRelatesTo['m.in_reply_to'];
-            if (mInReplyTo && mInReplyTo['event_id']) return mInReplyTo['event_id'];
+        if (ev.replyEventId) {
+            return ev.replyEventId;
         } else if (!SettingsStore.getValue("feature_thread") && ev.isThreadRelation) {
             return ev.threadRootId;
         }
@@ -232,7 +230,7 @@ export default class ReplyChain extends React.Component<IProps, IState> {
         return { body, html };
     }
 
-    public static makeReplyMixIn(ev: MatrixEvent) {
+    public static makeReplyMixIn(ev: MatrixEvent, renderIn?: string[]) {
         if (!ev) return {};
 
         const mixin: any = {
@@ -243,6 +241,10 @@ export default class ReplyChain extends React.Component<IProps, IState> {
             },
         };
 
+        if (renderIn) {
+            mixin['m.relates_to']['m.in_reply_to']['m.render_in'] = renderIn;
+        }
+
         /**
          * If the event replied is part of a thread
          * Add the `m.thread` relation so that clients
@@ -260,8 +262,25 @@ export default class ReplyChain extends React.Component<IProps, IState> {
         return mixin;
     }
 
-    public static hasReply(event: MatrixEvent) {
-        return Boolean(ReplyChain.getParentEventId(event));
+    private static DEFAULT_RENDER_TARGET = "m.room";
+
+    public static shouldDisplayReply(event: MatrixEvent, renderTarget = ReplyChain.DEFAULT_RENDER_TARGET): boolean {
+        const parentExist = Boolean(ReplyChain.getParentEventId(event));
+
+        const relations = event.getWireContent()["m.relates_to"];
+        const renderIn = relations?.["m.in_reply_to"]?.["m.render_in"];
+
+        const shouldRenderInTarget = !renderIn || renderIn.includes(renderTarget);
+
+        return parentExist && shouldRenderInTarget;
+    }
+
+    public static getRenderInMixin(relation?: IEventRelation): string[] {
+        const renderIn = ["m.room"];
+        if (relation?.rel_type === RelationType.Thread) {
+            renderIn.push(RelationType.Thread);
+        }
+        return renderIn;
     }
 
     componentDidMount() {

src/components/views/messages/MessageActionBar.tsx

@@ -382,7 +382,7 @@ export default class MessageActionBar extends React.PureComponent<IMessageAction
                 toolbarOpts.push(cancelSendingButton);
             }
 
-            if (this.props.isQuoteExpanded !== undefined && ReplyChain.hasReply(this.props.mxEvent)) {
+            if (this.props.isQuoteExpanded !== undefined && ReplyChain.shouldDisplayReply(this.props.mxEvent)) {
                 const expandClassName = classNames({
                     'mx_MessageActionBar_maskButton': true,
                     'mx_MessageActionBar_expandMessageButton': !this.props.isQuoteExpanded,

src/components/views/rooms/EventTile.tsx

@@ -17,7 +17,7 @@ limitations under the License.
 
 import React, { createRef } from 'react';
 import classNames from "classnames";
-import { EventType, MsgType } from "matrix-js-sdk/src/@types/event";
+import { EventType, MsgType, RelationType } from "matrix-js-sdk/src/@types/event";
 import { EventStatus, MatrixEvent } from "matrix-js-sdk/src/models/event";
 import { Relations } from "matrix-js-sdk/src/models/relations";
 import { RoomMember } from "matrix-js-sdk/src/models/room-member";
@@ -1330,7 +1330,12 @@ export default class EventTile extends React.Component<IProps, IState> {
             msgOption = readAvatars;
         }
 
-        const replyChain = haveTileForEvent(this.props.mxEvent) && ReplyChain.hasReply(this.props.mxEvent)
+        const renderTarget = this.props.tileShape === TileShape.Thread
+            ? RelationType.Thread
+            : "m.room";
+
+        const replyChain = haveTileForEvent(this.props.mxEvent)
+            && ReplyChain.shouldDisplayReply(this.props.mxEvent, renderTarget)
             ? <ReplyChain
                 parentEv={this.props.mxEvent}
                 onHeightChanged={this.props.onHeightChanged}

src/components/views/rooms/SendMessageComposer.tsx

@@ -57,22 +57,32 @@ import DocumentPosition from "../../../editor/position";
 import { ComposerType } from "../../../dispatcher/payloads/ComposerInsertPayload";
 import { getSlashCommand, isSlashCommand, runSlashCommand, shouldSendAnyway } from "../../../editor/commands";
 
+interface IAddReplyOpts {
+    permalinkCreator?: RoomPermalinkCreator;
+    includeLegacyFallback?: boolean;
+    renderIn?: string[];
+}
+
 function addReplyToMessageContent(
     content: IContent,
     replyToEvent: MatrixEvent,
-    permalinkCreator: RoomPermalinkCreator,
+    opts: IAddReplyOpts = {
+        includeLegacyFallback: true,
+    },
 ): void {
-    const replyContent = ReplyChain.makeReplyMixIn(replyToEvent);
+    const replyContent = ReplyChain.makeReplyMixIn(replyToEvent, opts.renderIn);
     Object.assign(content, replyContent);
 
-    // Part of Replies fallback support - prepend the text we're sending
-    // with the text we're replying to
-    const nestedReply = ReplyChain.getNestedReplyText(replyToEvent, permalinkCreator);
-    if (nestedReply) {
-        if (content.formatted_body) {
-            content.formatted_body = nestedReply.html + content.formatted_body;
+    if (opts.includeLegacyFallback) {
+        // Part of Replies fallback support - prepend the text we're sending
+        // with the text we're replying to
+        const nestedReply = ReplyChain.getNestedReplyText(replyToEvent, opts.permalinkCreator);
+        if (nestedReply) {
+            if (content.formatted_body) {
+                content.formatted_body = nestedReply.html + content.formatted_body;
+            }
+            content.body = nestedReply.body + content.body;
         }
-        content.body = nestedReply.body + content.body;
     }
 }
 
@@ -94,6 +104,7 @@ export function createMessageContent(
     replyToEvent: MatrixEvent,
     relation: IEventRelation,
     permalinkCreator: RoomPermalinkCreator,
+    includeReplyLegacyFallback = true,
 ): IContent {
     const isEmote = containsEmote(model);
     if (isEmote) {
@@ -116,7 +127,11 @@ export function createMessageContent(
     }
 
     if (replyToEvent) {
-        addReplyToMessageContent(content, replyToEvent, permalinkCreator);
+        addReplyToMessageContent(content, replyToEvent, {
+            permalinkCreator,
+            includeLegacyFallback: true,
+            renderIn: ReplyChain.getRenderInMixin(relation),
+        });
     }
 
     if (relation) {
@@ -155,6 +170,7 @@ interface ISendMessageComposerProps extends MatrixClientProps {
     replyToEvent?: MatrixEvent;
     disabled?: boolean;
     onChange?(model: EditorModel): void;
+    includeReplyLegacyFallback: boolean;
 }
 
 @replaceableComponent("views.rooms.SendMessageComposer")
@@ -169,6 +185,10 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
     private dispatcherRef: string;
     private sendHistoryManager: SendHistoryManager;
 
+    static defaultProps = {
+        includeReplyLegacyFallback: true,
+    };
+
     constructor(props: ISendMessageComposerProps, context: React.ContextType<typeof RoomContext>) {
         super(props);
         if (this.props.mxClient.isCryptoEnabled() && this.props.mxClient.isRoomEncrypted(this.props.room.roomId)) {
@@ -350,10 +370,14 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
                         return; // errored
                     }
 
+                    attachRelation(content, this.props.relation);
                     if (replyToEvent) {
-                        addReplyToMessageContent(content, replyToEvent, this.props.permalinkCreator);
+                        addReplyToMessageContent(content, replyToEvent, {
+                            permalinkCreator: this.props.permalinkCreator,
+                            includeLegacyFallback: true,
+                            renderIn: ReplyChain.getRenderInMixin(this.props.relation),
+                        });
                     }
-                    attachRelation(content, this.props.relation);
                 } else {
                     runSlashCommand(cmd, args, this.props.room.roomId, threadId);
                     shouldSend = false;
@@ -378,6 +402,7 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
                     replyToEvent,
                     this.props.relation,
                     this.props.permalinkCreator,
+                    this.props.includeReplyLegacyFallback,
                 );
             }
             // don't bother sending an empty message

test/components/views/rooms/SendMessageComposer-test.tsx

@@ -302,6 +302,7 @@ describe('<SendMessageComposer/>', () => {
                             rel_type: RelationType.Thread,
                             event_id: "myFakeThreadId",
                         }}
+                        includeReplyLegacyFallback={false}
                     />
                 </RoomContext.Provider>
             </MatrixClientContext.Provider>);