Mentions as links rte (#10422)

* bumps the RTE dependency to introduce user/room mention handling
* adds autocomplete behaviour to allow users to insert user and room mentions as links
* sets up tests for the autocomplete behaviour

package.json

@@ -61,7 +61,7 @@
     "dependencies": {
         "@babel/runtime": "^7.12.5",
         "@matrix-org/analytics-events": "^0.5.0",
-        "@matrix-org/matrix-wysiwyg": "^1.1.1",
+        "@matrix-org/matrix-wysiwyg": "^1.4.0",
         "@matrix-org/react-sdk-module-api": "^0.0.4",
         "@sentry/browser": "^7.0.0",
         "@sentry/tracing": "^7.0.0",

res/css/views/rooms/wysiwyg_composer/_SendWysiwygComposer.pcss

@@ -84,3 +84,10 @@ limitations under the License.
         border-color: $quaternary-content;
     }
 }
+
+.mx_SendWysiwygComposer_AutoCompleteWrapper {
+    position: relative;
+    > .mx_Autocomplete {
+        min-width: 100%;
+    }
+}

res/css/views/rooms/wysiwyg_composer/components/_Editor.pcss

@@ -100,6 +100,11 @@ limitations under the License.
                 padding: unset;
             }
         }
+
+        /* this selector represents what will become a pill */
+        a[data-mention-type] {
+            cursor: text;
+        }
     }
 
     .mx_WysiwygComposer_Editor_content_placeholder::before {

src/components/views/rooms/wysiwyg_composer/components/WysiwygAutocomplete.tsx

@@ -0,0 +1,137 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React, { ForwardedRef, forwardRef } from "react";
+import { MatrixClient, Room } from "matrix-js-sdk/src/matrix";
+import { FormattingFunctions, MappedSuggestion } from "@matrix-org/matrix-wysiwyg";
+
+import { useRoomContext } from "../../../../../contexts/RoomContext";
+import Autocomplete from "../../Autocomplete";
+import { ICompletion } from "../../../../../autocomplete/Autocompleter";
+import { useMatrixClientContext } from "../../../../../contexts/MatrixClientContext";
+
+interface WysiwygAutocompleteProps {
+    /**
+     * The suggestion output from the rust model is used to build the query that is
+     * passed to the `<Autocomplete />` component
+     */
+    suggestion: MappedSuggestion | null;
+
+    /**
+     * This handler will be called with the href and display text for a mention on clicking
+     * a mention in the autocomplete list or pressing enter on a selected item
+     */
+    handleMention: FormattingFunctions["mention"];
+}
+
+/**
+ * Builds the query for the `<Autocomplete />` component from the rust suggestion. This
+ * will change as we implement handling / commands.
+ *
+ * @param suggestion  - represents if the rust model is tracking a potential mention
+ * @returns an empty string if we can not generate a query, otherwise a query beginning
+ * with @ for a user query, # for a room or space query
+ */
+function buildQuery(suggestion: MappedSuggestion | null): string {
+    if (!suggestion || !suggestion.keyChar || suggestion.type === "command") {
+        // if we have an empty key character, we do not build a query
+        // TODO implement the command functionality
+        return "";
+    }
+
+    return `${suggestion.keyChar}${suggestion.text}`;
+}
+
+/**
+ * Given a room type mention, determine the text that should be displayed in the mention
+ * TODO expand this function to more generally handle outputting the display text from a
+ * given completion
+ *
+ * @param completion - the item selected from the autocomplete, currently treated as a room completion
+ * @param client - the MatrixClient is required for us to look up the correct room mention text
+ * @returns the text to display in the mention
+ */
+function getRoomMentionText(completion: ICompletion, client: MatrixClient): string {
+    const roomId = completion.completionId;
+    const alias = completion.completion;
+
+    let roomForAutocomplete: Room | null | undefined;
+
+    // Not quite sure if the logic here makes sense - specifically calling .getRoom with an alias
+    // that doesn't start with #, but keeping the logic the same as in PartCreator.roomPill for now
+    if (roomId) {
+        roomForAutocomplete = client.getRoom(roomId);
+    } else if (!alias.startsWith("#")) {
+        roomForAutocomplete = client.getRoom(alias);
+    } else {
+        roomForAutocomplete = client.getRooms().find((r) => {
+            return r.getCanonicalAlias() === alias || r.getAltAliases().includes(alias);
+        });
+    }
+
+    // if we haven't managed to find the room, use the alias as a fallback
+    return roomForAutocomplete?.name || alias;
+}
+
+/**
+ * Given the current suggestion from the rust model and a handler function, this component
+ * will display the legacy `<Autocomplete />` component (as used in the BasicMessageComposer)
+ * and call the handler function with the required arguments when a mention is selected
+ *
+ * @param props.ref - the ref will be attached to the rendered `<Autocomplete />` component
+ */
+const WysiwygAutocomplete = forwardRef(
+    ({ suggestion, handleMention }: WysiwygAutocompleteProps, ref: ForwardedRef<Autocomplete>): JSX.Element | null => {
+        const { room } = useRoomContext();
+        const client = useMatrixClientContext();
+
+        function handleConfirm(completion: ICompletion): void {
+            if (!completion.href) return;
+
+            switch (completion.type) {
+                case "user":
+                    handleMention(completion.href, completion.completion);
+                    break;
+                case "room": {
+                    handleMention(completion.href, getRoomMentionText(completion, client));
+                    break;
+                }
+                // TODO implement the command functionality
+                // case "command":
+                //     console.log("/command functionality not yet in place");
+                //     break;
+                default:
+                    break;
+            }
+        }
+
+        return room ? (
+            <div className="mx_SendWysiwygComposer_AutoCompleteWrapper" data-testid="autocomplete-wrapper">
+                <Autocomplete
+                    ref={ref}
+                    query={buildQuery(suggestion)}
+                    onConfirm={handleConfirm}
+                    selection={{ start: 0, end: 0 }}
+                    room={room}
+                />
+            </div>
+        ) : null;
+    },
+);
+
+WysiwygAutocomplete.displayName = "WysiwygAutocomplete";
+
+export { WysiwygAutocomplete };

src/components/views/rooms/wysiwyg_composer/components/WysiwygComposer.tsx

@@ -14,15 +14,21 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { memo, MutableRefObject, ReactNode, useEffect } from "react";
+import React, { memo, MutableRefObject, ReactNode, useEffect, useRef } from "react";
 import { useWysiwyg, FormattingFunctions } from "@matrix-org/matrix-wysiwyg";
 import classNames from "classnames";
 
+import Autocomplete from "../../Autocomplete";
+import { WysiwygAutocomplete } from "./WysiwygAutocomplete";
 import { FormattingButtons } from "./FormattingButtons";
 import { Editor } from "./Editor";
 import { useInputEventProcessor } from "../hooks/useInputEventProcessor";
 import { useSetCursorPosition } from "../hooks/useSetCursorPosition";
 import { useIsFocused } from "../hooks/useIsFocused";
+import { useRoomContext } from "../../../../../contexts/RoomContext";
+import defaultDispatcher from "../../../../../dispatcher/dispatcher";
+import { Action } from "../../../../../dispatcher/actions";
+import { parsePermalink } from "../../../../../utils/permalinks/Permalinks";
 
 interface WysiwygComposerProps {
     disabled?: boolean;
@@ -47,9 +53,20 @@ export const WysiwygComposer = memo(function WysiwygComposer({
     rightComponent,
     children,
 }: WysiwygComposerProps) {
-    const inputEventProcessor = useInputEventProcessor(onSend, initialContent);
+    const { room } = useRoomContext();
+    const autocompleteRef = useRef<Autocomplete | null>(null);
 
-    const { ref, isWysiwygReady, content, actionStates, wysiwyg } = useWysiwyg({ initialContent, inputEventProcessor });
+    const inputEventProcessor = useInputEventProcessor(onSend, autocompleteRef, initialContent);
+    const { ref, isWysiwygReady, content, actionStates, wysiwyg, suggestion } = useWysiwyg({
+        initialContent,
+        inputEventProcessor,
+    });
+    const { isFocused, onFocus } = useIsFocused();
+
+    const isReady = isWysiwygReady && !disabled;
+    const computedPlaceholder = (!content && placeholder) || undefined;
+
+    useSetCursorPosition(!isReady, ref);
 
     useEffect(() => {
         if (!disabled && content !== null) {
@@ -57,11 +74,32 @@ export const WysiwygComposer = memo(function WysiwygComposer({
         }
     }, [onChange, content, disabled]);
 
-    const isReady = isWysiwygReady && !disabled;
+    useEffect(() => {
-    useSetCursorPosition(!isReady, ref);
+        function handleClick(e: Event): void {
+            e.preventDefault();
+            if (
+                e.target &&
+                e.target instanceof HTMLAnchorElement &&
+                e.target.getAttribute("data-mention-type") === "user"
+            ) {
+                const parsedLink = parsePermalink(e.target.href);
+                if (room && parsedLink?.userId)
+                    defaultDispatcher.dispatch({
+                        action: Action.ViewUser,
+                        member: room.getMember(parsedLink.userId),
+                    });
+            }
+        }
 
-    const { isFocused, onFocus } = useIsFocused();
+        const mentions = ref.current?.querySelectorAll("a[data-mention-type]");
-    const computedPlaceholder = (!content && placeholder) || undefined;
+        if (mentions) {
+            mentions.forEach((mention) => mention.addEventListener("click", handleClick));
+        }
+
+        return () => {
+            if (mentions) mentions.forEach((mention) => mention.removeEventListener("click", handleClick));
+        };
+    }, [ref, room, content]);
 
     return (
         <div
@@ -70,6 +108,7 @@ export const WysiwygComposer = memo(function WysiwygComposer({
             onFocus={onFocus}
             onBlur={onFocus}
         >
+            <WysiwygAutocomplete ref={autocompleteRef} suggestion={suggestion} handleMention={wysiwyg.mention} />
             <FormattingButtons composer={wysiwyg} actionStates={actionStates} />
             <Editor
                 ref={ref}

src/components/views/rooms/wysiwyg_composer/hooks/useInputEventProcessor.ts

@@ -32,9 +32,11 @@ import { useMatrixClientContext } from "../../../../../contexts/MatrixClientCont
 import { isCaretAtEnd, isCaretAtStart } from "../utils/selection";
 import { getEventsFromEditorStateTransfer, getEventsFromRoom } from "../utils/event";
 import { endEditing } from "../utils/editing";
+import Autocomplete from "../../Autocomplete";
 
 export function useInputEventProcessor(
     onSend: () => void,
+    autocompleteRef: React.RefObject<Autocomplete>,
     initialContent?: string,
 ): (event: WysiwygEvent, composer: Wysiwyg, editor: HTMLElement) => WysiwygEvent | null {
     const roomContext = useRoomContext();
@@ -51,6 +53,10 @@ export function useInputEventProcessor(
             const send = (): void => {
                 event.stopPropagation?.();
                 event.preventDefault?.();
+                // do not send the message if we have the autocomplete open, regardless of settings
+                if (autocompleteRef?.current && !autocompleteRef.current.state.hide) {
+                    return;
+                }
                 onSend();
             };
 
@@ -65,12 +71,13 @@ export function useInputEventProcessor(
                     roomContext,
                     composerContext,
                     mxClient,
+                    autocompleteRef,
                 );
             } else {
                 return handleInputEvent(event, send, isCtrlEnterToSend);
             }
         },
-        [isCtrlEnterToSend, onSend, initialContent, roomContext, composerContext, mxClient],
+        [isCtrlEnterToSend, onSend, initialContent, roomContext, composerContext, mxClient, autocompleteRef],
     );
 }
 
@@ -85,12 +92,51 @@ function handleKeyboardEvent(
     roomContext: IRoomState,
     composerContext: ComposerContextState,
     mxClient: MatrixClient,
+    autocompleteRef: React.RefObject<Autocomplete>,
 ): KeyboardEvent | null {
     const { editorStateTransfer } = composerContext;
     const isEditing = Boolean(editorStateTransfer);
     const isEditorModified = isEditing ? initialContent !== composer.content() : composer.content().length !== 0;
     const action = getKeyBindingsManager().getMessageComposerAction(event);
 
+    const autocompleteIsOpen = autocompleteRef?.current && !autocompleteRef.current.state.hide;
+
+    // we need autocomplete to take priority when it is open for using enter to select
+    if (autocompleteIsOpen) {
+        let handled = false;
+        const autocompleteAction = getKeyBindingsManager().getAutocompleteAction(event);
+        const component = autocompleteRef.current;
+        if (component && component.countCompletions() > 0) {
+            switch (autocompleteAction) {
+                case KeyBindingAction.ForceCompleteAutocomplete:
+                case KeyBindingAction.CompleteAutocomplete:
+                    autocompleteRef.current.onConfirmCompletion();
+                    handled = true;
+                    break;
+                case KeyBindingAction.PrevSelectionInAutocomplete:
+                    autocompleteRef.current.moveSelection(-1);
+                    handled = true;
+                    break;
+                case KeyBindingAction.NextSelectionInAutocomplete:
+                    autocompleteRef.current.moveSelection(1);
+                    handled = true;
+                    break;
+                case KeyBindingAction.CancelAutocomplete:
+                    autocompleteRef.current.onEscape(event as {} as React.KeyboardEvent);
+                    handled = true;
+                    break;
+                default:
+                    break; // don't return anything, allow event to pass through
+            }
+        }
+
+        if (handled) {
+            event.preventDefault();
+            event.stopPropagation();
+            return event;
+        }
+    }
+
     switch (action) {
         case KeyBindingAction.SendMessage:
             send();

test/components/views/rooms/wysiwyg_composer/SendWysiwygComposer-test.tsx

@@ -93,15 +93,15 @@ describe("SendWysiwygComposer", () => {
         customRender(jest.fn(), jest.fn(), false, true);
 
         // Then
-        await waitFor(() => expect(screen.getByTestId("WysiwygComposer")).toBeTruthy());
+        expect(await screen.findByTestId("WysiwygComposer")).toBeInTheDocument();
     });
 
-    it("Should render PlainTextComposer when isRichTextEnabled is at false", () => {
+    it("Should render PlainTextComposer when isRichTextEnabled is at false", async () => {
         // When
         customRender(jest.fn(), jest.fn(), false, false);
 
         // Then
-        expect(screen.getByTestId("PlainTextComposer")).toBeTruthy();
+        expect(await screen.findByTestId("PlainTextComposer")).toBeInTheDocument();
     });
 
     describe.each([{ isRichTextEnabled: true }, { isRichTextEnabled: false }])(

test/components/views/rooms/wysiwyg_composer/components/WysiwygAutocomplete-test.tsx

@@ -0,0 +1,120 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import "@testing-library/jest-dom";
+import React, { createRef } from "react";
+import { render, screen, waitFor } from "@testing-library/react";
+
+import MatrixClientContext from "../../../../../../src/contexts/MatrixClientContext";
+import RoomContext from "../../../../../../src/contexts/RoomContext";
+import { WysiwygAutocomplete } from "../../../../../../src/components/views/rooms/wysiwyg_composer/components/WysiwygAutocomplete";
+import { getRoomContext, mkStubRoom, stubClient } from "../../../../../test-utils";
+import Autocomplete from "../../../../../../src/components/views/rooms/Autocomplete";
+import Autocompleter, { ICompletion } from "../../../../../../src/autocomplete/Autocompleter";
+import AutocompleteProvider from "../../../../../../src/autocomplete/AutocompleteProvider";
+
+const mockCompletion: ICompletion[] = [
+    {
+        type: "user",
+        completion: "user_1",
+        completionId: "@user_1:host.local",
+        range: { start: 1, end: 1 },
+        component: <div>user_1</div>,
+    },
+    {
+        type: "user",
+        completion: "user_2",
+        completionId: "@user_2:host.local",
+        range: { start: 1, end: 1 },
+        component: <div>user_2</div>,
+    },
+];
+
+const constructMockProvider = (data: ICompletion[]) =>
+    ({
+        getCompletions: jest.fn().mockImplementation(async () => data),
+        getName: jest.fn().mockReturnValue("test provider"),
+        renderCompletions: jest.fn().mockImplementation((components) => components),
+    } as unknown as AutocompleteProvider);
+
+describe("WysiwygAutocomplete", () => {
+    beforeAll(() => {
+        // scrollTo not implemented in JSDOM
+        window.HTMLElement.prototype.scrollTo = function () {};
+    });
+
+    afterAll(() => {
+        jest.restoreAllMocks();
+    });
+
+    const autocompleteRef = createRef<Autocomplete>();
+    const getCompletionsSpy = jest.spyOn(Autocompleter.prototype, "getCompletions").mockResolvedValue([
+        {
+            completions: mockCompletion,
+            provider: constructMockProvider(mockCompletion),
+            command: { command: ["truthy"] as RegExpExecArray }, // needed for us to unhide the autocomplete when testing
+        },
+    ]);
+    const mockHandleMention = jest.fn();
+
+    const renderComponent = (props = {}) => {
+        const mockClient = stubClient();
+        const mockRoom = mkStubRoom("test_room", "test_room", mockClient);
+        const mockRoomContext = getRoomContext(mockRoom, {});
+
+        return render(
+            <MatrixClientContext.Provider value={mockClient}>
+                <RoomContext.Provider value={mockRoomContext}>
+                    <WysiwygAutocomplete
+                        ref={autocompleteRef}
+                        suggestion={null}
+                        handleMention={mockHandleMention}
+                        {...props}
+                    />
+                </RoomContext.Provider>
+            </MatrixClientContext.Provider>,
+        );
+    };
+
+    it("does not show the autocomplete when room is undefined", () => {
+        render(<WysiwygAutocomplete ref={autocompleteRef} suggestion={null} handleMention={mockHandleMention} />);
+        expect(screen.queryByTestId("autocomplete-wrapper")).not.toBeInTheDocument();
+    });
+
+    it("does not call for suggestions with a null suggestion prop", async () => {
+        // render the component, the default props have suggestion = null
+        renderComponent();
+
+        // check that getCompletions is not called, and we have no suggestions
+        expect(getCompletionsSpy).not.toHaveBeenCalled();
+        expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+    });
+
+    it("calls getCompletions when given a valid suggestion prop", async () => {
+        renderComponent({ suggestion: { keyChar: "@", text: "abc", type: "mention" } });
+
+        // wait for getCompletions to have been called
+        await waitFor(() => {
+            expect(getCompletionsSpy).toHaveBeenCalled();
+        });
+
+        // check that some suggestions are shown
+        expect(screen.getByRole("presentation")).toBeInTheDocument();
+
+        // and that they are the mock completions
+        mockCompletion.forEach(({ completion }) => expect(screen.getByText(completion)).toBeInTheDocument());
+    });
+});

test/components/views/rooms/wysiwyg_composer/components/WysiwygComposer-test.tsx

@@ -21,7 +21,7 @@ import userEvent from "@testing-library/user-event";
 
 import { WysiwygComposer } from "../../../../../../src/components/views/rooms/wysiwyg_composer/components/WysiwygComposer";
 import SettingsStore from "../../../../../../src/settings/SettingsStore";
-import { createTestClient, flushPromises, mockPlatformPeg } from "../../../../../test-utils";
+import { flushPromises, mockPlatformPeg, stubClient, mkStubRoom } from "../../../../../test-utils";
 import defaultDispatcher from "../../../../../../src/dispatcher/dispatcher";
 import * as EventUtils from "../../../../../../src/utils/EventUtils";
 import { Action } from "../../../../../../src/dispatcher/actions";
@@ -36,11 +36,25 @@ import EditorStateTransfer from "../../../../../../src/utils/EditorStateTransfer
 import { SubSelection } from "../../../../../../src/components/views/rooms/wysiwyg_composer/types";
 import { setSelection } from "../../../../../../src/components/views/rooms/wysiwyg_composer/utils/selection";
 import { parseEditorStateTransfer } from "../../../../../../src/components/views/rooms/wysiwyg_composer/hooks/useInitialContent";
+import Autocompleter, { ICompletion } from "../../../../../../src/autocomplete/Autocompleter";
+import AutocompleteProvider from "../../../../../../src/autocomplete/AutocompleteProvider";
+import * as Permalinks from "../../../../../../src/utils/permalinks/Permalinks";
+import { PermalinkParts } from "../../../../../../src/utils/permalinks/PermalinkConstructor";
 
 describe("WysiwygComposer", () => {
     const customRender = (onChange = jest.fn(), onSend = jest.fn(), disabled = false, initialContent?: string) => {
+        const { mockClient, defaultRoomContext } = createMocks();
         return render(
-            <WysiwygComposer onChange={onChange} onSend={onSend} disabled={disabled} initialContent={initialContent} />,
+            <MatrixClientContext.Provider value={mockClient}>
+                <RoomContext.Provider value={defaultRoomContext}>
+                    <WysiwygComposer
+                        onChange={onChange}
+                        onSend={onSend}
+                        disabled={disabled}
+                        initialContent={initialContent}
+                    />
+                </RoomContext.Provider>
+            </MatrixClientContext.Provider>,
         );
     };
 
@@ -48,12 +62,12 @@ describe("WysiwygComposer", () => {
         jest.resetAllMocks();
     });
 
-    it("Should have contentEditable at false when disabled", () => {
+    it("Should have contentEditable at false when disabled", async () => {
         // When
         customRender(jest.fn(), jest.fn(), true);
 
         // Then
-        expect(screen.getByRole("textbox")).toHaveAttribute("contentEditable", "false");
+        await waitFor(() => expect(screen.getByRole("textbox")).toHaveAttribute("contentEditable", "false"));
     });
 
     describe("Standard behavior", () => {
@@ -144,6 +158,199 @@ describe("WysiwygComposer", () => {
         });
     });
 
+    describe("Mentions", () => {
+        const dispatchSpy = jest.spyOn(defaultDispatcher, "dispatch");
+
+        const mockCompletions: ICompletion[] = [
+            {
+                type: "user",
+                href: "www.user1.com",
+                completion: "user_1",
+                completionId: "@user_1:host.local",
+                range: { start: 1, end: 1 },
+                component: <div>user_1</div>,
+            },
+            {
+                type: "user",
+                href: "www.user2.com",
+                completion: "user_2",
+                completionId: "@user_2:host.local",
+                range: { start: 1, end: 1 },
+                component: <div>user_2</div>,
+            },
+            {
+                // no href user
+                type: "user",
+                completion: "user_without_href",
+                completionId: "@user_3:host.local",
+                range: { start: 1, end: 1 },
+                component: <div>user_without_href</div>,
+            },
+            {
+                type: "room",
+                href: "www.room1.com",
+                completion: "#room_with_completion_id",
+                completionId: "@room_1:host.local",
+                range: { start: 1, end: 1 },
+                component: <div>room_with_completion_id</div>,
+            },
+            {
+                type: "room",
+                href: "www.room2.com",
+                completion: "#room_without_completion_id",
+                range: { start: 1, end: 1 },
+                component: <div>room_without_completion_id</div>,
+            },
+        ];
+
+        const constructMockProvider = (data: ICompletion[]) =>
+            ({
+                getCompletions: jest.fn().mockImplementation(async () => data),
+                getName: jest.fn().mockReturnValue("test provider"),
+                renderCompletions: jest.fn().mockImplementation((components) => components),
+            } as unknown as AutocompleteProvider);
+
+        // for each test we will insert input simulating a user mention
+        const insertMentionInput = async () => {
+            fireEvent.input(screen.getByRole("textbox"), {
+                data: "@abc",
+                inputType: "insertText",
+            });
+
+            // the autocomplete suggestions container has the presentation role, wait for it to be present
+            expect(await screen.findByRole("presentation")).toBeInTheDocument();
+        };
+
+        beforeEach(async () => {
+            // setup the required spies
+            jest.spyOn(Autocompleter.prototype, "getCompletions").mockResolvedValue([
+                {
+                    completions: mockCompletions,
+                    provider: constructMockProvider(mockCompletions),
+                    command: { command: ["truthy"] as RegExpExecArray }, // needed for us to unhide the autocomplete when testing
+                },
+            ]);
+            jest.spyOn(Permalinks, "parsePermalink").mockReturnValue({
+                userId: "mockParsedUserId",
+            } as unknown as PermalinkParts);
+
+            // then render the component and wait for the composer to be ready
+            customRender();
+            await waitFor(() => expect(screen.getByRole("textbox")).toHaveAttribute("contentEditable", "true"));
+        });
+
+        afterEach(() => {
+            jest.clearAllMocks();
+        });
+
+        it("shows the autocomplete when text has @ prefix and autoselects the first item", async () => {
+            await insertMentionInput();
+            expect(screen.getByText(mockCompletions[0].completion)).toHaveAttribute("aria-selected", "true");
+        });
+
+        it("pressing up and down arrows allows us to change the autocomplete selection", async () => {
+            await insertMentionInput();
+
+            // press the down arrow - nb using .keyboard allows us to not have to specify a node, which
+            // means that we know the autocomplete is correctly catching the event
+            await userEvent.keyboard("{ArrowDown}");
+            expect(screen.getByText(mockCompletions[0].completion)).toHaveAttribute("aria-selected", "false");
+            expect(screen.getByText(mockCompletions[1].completion)).toHaveAttribute("aria-selected", "true");
+
+            // reverse the process and check again
+            await userEvent.keyboard("{ArrowUp}");
+            expect(screen.getByText(mockCompletions[0].completion)).toHaveAttribute("aria-selected", "true");
+            expect(screen.getByText(mockCompletions[1].completion)).toHaveAttribute("aria-selected", "false");
+        });
+
+        it("pressing enter selects the mention and inserts it into the composer as a link", async () => {
+            await insertMentionInput();
+
+            // press enter
+            await userEvent.keyboard("{Enter}");
+
+            // check that it closes the autocomplete
+            await waitFor(() => {
+                expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+            });
+
+            // check that it inserts the completion text as a link
+            expect(screen.getByRole("link", { name: mockCompletions[0].completion })).toBeInTheDocument();
+        });
+
+        it("clicking on a mention in the composer dispatches the correct action", async () => {
+            await insertMentionInput();
+
+            // press enter
+            await userEvent.keyboard("{Enter}");
+
+            // check that it closes the autocomplete
+            await waitFor(() => {
+                expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+            });
+
+            // click on the user mention link that has been inserted
+            await userEvent.click(screen.getByRole("link", { name: mockCompletions[0].completion }));
+            expect(dispatchSpy).toHaveBeenCalledTimes(1);
+
+            // this relies on the output from the mock function in mkStubRoom
+            expect(dispatchSpy).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    action: Action.ViewUser,
+                    member: expect.objectContaining({
+                        userId: mkStubRoom(undefined, undefined, undefined).getMember("any")?.userId,
+                    }),
+                }),
+            );
+        });
+
+        it("selecting a mention without a href closes the autocomplete but does not insert a mention", async () => {
+            await insertMentionInput();
+
+            // select the relevant user by clicking
+            await userEvent.click(screen.getByText("user_without_href"));
+
+            // check that it closes the autocomplete
+            await waitFor(() => {
+                expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+            });
+
+            // check that it has not inserted a link
+            expect(screen.queryByRole("link", { name: "user_without_href" })).not.toBeInTheDocument();
+        });
+
+        it("selecting a room mention with a completionId uses client.getRoom", async () => {
+            await insertMentionInput();
+
+            // select the room suggestion by clicking
+            await userEvent.click(screen.getByText("room_with_completion_id"));
+
+            // check that it closes the autocomplete
+            await waitFor(() => {
+                expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+            });
+
+            // check that it has inserted a link and looked up the name from the mock client
+            // which will always return 'My room'
+            expect(screen.getByRole("link", { name: "My room" })).toBeInTheDocument();
+        });
+
+        it("selecting a room mention without a completionId uses client.getRooms", async () => {
+            await insertMentionInput();
+
+            // select the room suggestion
+            await userEvent.click(screen.getByText("room_without_completion_id"));
+
+            // check that it closes the autocomplete
+            await waitFor(() => {
+                expect(screen.queryByRole("presentation")).not.toBeInTheDocument();
+            });
+
+            // check that it has inserted a link and falls back to the completion text
+            expect(screen.getByRole("link", { name: "#room_without_completion_id" })).toBeInTheDocument();
+        });
+    });
+
     describe("When settings require Ctrl+Enter to send", () => {
         const onChange = jest.fn();
         const onSend = jest.fn();
@@ -241,10 +448,11 @@ describe("WysiwygComposer", () => {
 
         const setup = async (
             editorState?: EditorStateTransfer,
-            client = createTestClient(),
+            client = stubClient(),
             roomContext = defaultRoomContext,
         ) => {
             const spyDispatcher = jest.spyOn(defaultDispatcher, "dispatch");
+
             customRender(client, roomContext, editorState);
             await waitFor(() => expect(screen.getByRole("textbox")).toHaveAttribute("contentEditable", "true"));
             return { textbox: screen.getByRole("textbox"), spyDispatcher };

test/components/views/rooms/wysiwyg_composer/utils.ts

@@ -16,12 +16,12 @@ limitations under the License.
 
 import { EventTimeline, MatrixEvent } from "matrix-js-sdk/src/matrix";
 
-import { createTestClient, getRoomContext, mkEvent, mkStubRoom } from "../../../../test-utils";
+import { getRoomContext, mkEvent, mkStubRoom, stubClient } from "../../../../test-utils";
 import { IRoomState } from "../../../../../src/components/structures/RoomView";
 import EditorStateTransfer from "../../../../../src/utils/EditorStateTransfer";
 
 export function createMocks(eventContent = "Replying <strong>to</strong> this new content") {
-    const mockClient = createTestClient();
+    const mockClient = stubClient();
     const mockEvent = mkEvent({
         type: "m.room.message",
         room: "myfakeroom",

yarn.lock

@@ -1664,10 +1664,10 @@
   resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-js/-/matrix-sdk-crypto-js-0.1.0-alpha.4.tgz#1b20294e0354c3dcc9c7dc810d883198a4042f04"
   integrity sha512-mdaDKrw3P5ZVCpq0ioW0pV6ihviDEbS8ZH36kpt9stLKHwwDSopPogE6CkQhi0B1jn1yBUtOYi32mBV/zcOR7g==
 
-"@matrix-org/matrix-wysiwyg@^1.1.1":
+"@matrix-org/matrix-wysiwyg@^1.4.0":
-  version "1.3.0"
+  version "1.4.0"
-  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-wysiwyg/-/matrix-wysiwyg-1.3.0.tgz#647837be552c1a96ca8157e0dc0d7d8f897fcbe2"
+  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-wysiwyg/-/matrix-wysiwyg-1.4.0.tgz#b04f4c05c8117c0917f9a1401bb1d9c5f976052c"
-  integrity sha512-uHcPYP+mriJZcI54lDBpO+wPGDli/+VEL/NjuW+BBgt7PLViSa4xaGdD7K+yUBgntRdbJ/J4fo+lYB06kqF+sA==
+  integrity sha512-NIxX1oia61zut/DA7fUCCQfOhWKLbVDmPrDeUeX40NgXZRROhLPF1/jcOKgAnXK8yqflmNrVlX/dlUVcfj/kqw==
 
 "@matrix-org/olm@https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.14.tgz":
   version "3.2.14"