Allow filtering room list during treeview navigation

src/accessibility/RovingTabIndex.tsx

@@ -123,9 +123,14 @@ export const reducer = (state: IState, action: IAction) => {
 
             if (state.refs.splice(oldIndex, 1)[0] === state.activeRef) {
                 // we just removed the active ref, need to replace it
-                // pick the ref which is now in the index the old ref was in
-                const len = state.refs.length;
-                state.activeRef = oldIndex >= len ? state.refs[len - 1] : state.refs[oldIndex];
+                // pick the ref closest to the index the old ref was in
+                if (oldIndex >= state.refs.length) {
+                    state.activeRef = findSiblingElement(state.refs, state.refs.length - 1, true);
+                } else {
+                    state.activeRef = findSiblingElement(state.refs, oldIndex)
+                        || findSiblingElement(state.refs, oldIndex, true);
+                }
+                state.activeRef?.current?.focus();
             }
 
             // update the refs list

src/components/structures/LeftPanel.tsx

@@ -42,6 +42,7 @@ import { getKeyBindingsManager, RoomListAction } from "../../KeyBindingsManager"
 import UIStore from "../../stores/UIStore";
 import { findSiblingElement, IState as IRovingTabIndexState } from "../../accessibility/RovingTabIndex";
 import MatrixClientContext from "../../contexts/MatrixClientContext";
+import { Key } from "../../Keyboard";
 
 interface IProps {
     isMinimized: boolean;
@@ -304,6 +305,19 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         }
     };
 
+    private onRoomListKeydown = (ev: React.KeyboardEvent) => {
+        // we cannot handle Space as that is an activation key for all focusable elements in this widget
+        if (ev.key.length === 1) {
+            ev.preventDefault();
+            ev.stopPropagation();
+            this.roomSearchRef.current?.appendChar(ev.key);
+        } else if (ev.key === Key.BACKSPACE) {
+            ev.preventDefault();
+            ev.stopPropagation();
+            this.roomSearchRef.current?.backspace();
+        }
+    };
+
     private selectRoom = () => {
         const firstRoom = this.listContainerRef.current.querySelector<HTMLDivElement>(".mx_RoomTile");
         if (firstRoom) {
@@ -411,6 +425,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                             // Firefox sometimes makes this element focusable due to
                             // overflow:scroll;, so force it out of tab order.
                             tabIndex={-1}
+                            onKeyDown={this.onRoomListKeydown}
                         >
                             { roomList }
                         </div>

src/components/structures/RoomSearch.tsx

@@ -214,4 +214,16 @@ export default class RoomSearch extends React.PureComponent<IProps, IState> {
             </div>
         );
     }
+
+    public appendChar(char: string): void {
+        this.setState({
+            query: this.state.query + char,
+        });
+    }
+
+    public backspace(): void {
+        this.setState({
+            query: this.state.query.substring(0, this.state.query.length - 1),
+        });
+    }
 }

test/accessibility/RovingTabIndex-test.tsx

@@ -45,6 +45,11 @@ const button2 = <Button key={2}>b</Button>;
 const button3 = <Button key={3}>c</Button>;
 const button4 = <Button key={4}>d</Button>;
 
+// mock offsetParent
+Object.defineProperty(HTMLElement.prototype, "offsetParent", {
+    get() { return this.parentNode; },
+});
+
 describe("RovingTabIndex", () => {
     it("RovingTabIndexProvider renders children as expected", () => {
         const wrapper = mount(<RovingTabIndexProvider>