Add option to display tooltip on link hover

src/BasePlatform.ts

@@ -222,6 +222,14 @@ export default abstract class BasePlatform {
         }
     }
 
+    /**
+     * Returns true if the platform requires URL previews in tooltips, otherwise false.
+     * @returns {boolean} whether the platform requires URL previews in tooltips
+     */
+    public needsUrlTooltips(): boolean {
+        return false;
+    }
+
     /**
      * Returns a promise that resolves to a string representing the current version of the application.
      */

src/components/views/elements/LinkWithTooltip.tsx

@@ -0,0 +1,44 @@
+/*
+ Copyright 2022 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 from 'react';
+
+import TextWithTooltip from './TextWithTooltip';
+
+interface IProps extends Omit<React.ComponentProps<typeof TextWithTooltip>, "tabIndex" | "onClick" > {}
+
+export default class LinkWithTooltip extends React.Component<IProps> {
+    constructor(props: IProps) {
+        super(props);
+    }
+
+    public render(): JSX.Element {
+        const { children, tooltip, ...props } = this.props;
+
+        return (
+            <TextWithTooltip
+                // Disable focusing on the tooltip target to avoid double / nested focus. The contained anchor element
+                // itself allows focusing which also triggers the tooltip.
+                tabIndex={-1}
+                tooltip={tooltip}
+                onClick={e => (e.target as HTMLElement).blur()} // Force tooltip to hide on clickout
+                {...props}
+            >
+                { children }
+            </TextWithTooltip>
+        );
+    }
+}

src/components/views/elements/TextWithTooltip.tsx

@@ -14,12 +14,12 @@
  limitations under the License.
  */
 
-import React from 'react';
+import React, { HTMLAttributes } from 'react';
 import classNames from 'classnames';
 
 import TooltipTarget from './TooltipTarget';
 
-interface IProps {
+interface IProps extends HTMLAttributes<HTMLSpanElement> {
     class?: string;
     tooltipClass?: string;
     tooltip: React.ReactNode;

src/components/views/messages/EditHistoryMessage.tsx

@@ -22,6 +22,7 @@ import * as HtmlUtils from '../../../HtmlUtils';
 import { editBodyDiffToHtml } from '../../../utils/MessageDiffUtils';
 import { formatTime } from '../../../DateUtils';
 import { pillifyLinks, unmountPills } from '../../../utils/pillify';
+import { tooltipifyLinks, unmountTooltips } from '../../../utils/tooltipify';
 import { _t } from '../../../languageHandler';
 import { MatrixClientPeg } from '../../../MatrixClientPeg';
 import Modal from '../../../Modal';
@@ -52,6 +53,7 @@ interface IState {
 export default class EditHistoryMessage extends React.PureComponent<IProps, IState> {
     private content = createRef<HTMLDivElement>();
     private pills: Element[] = [];
+    private tooltips: Element[] = [];
 
     constructor(props: IProps) {
         super(props);
@@ -93,12 +95,21 @@ export default class EditHistoryMessage extends React.PureComponent<IProps, ISta
         }
     }
 
+    private tooltipifyLinks(): void {
+        // not present for redacted events
+        if (this.content.current) {
+            tooltipifyLinks(this.content.current.children, this.pills, this.tooltips);
+        }
+    }
+
     public componentDidMount(): void {
         this.pillifyLinks();
+        this.tooltipifyLinks();
     }
 
     public componentWillUnmount(): void {
         unmountPills(this.pills);
+        unmountTooltips(this.tooltips);
         const event = this.props.mxEvent;
         if (event.localRedactionEvent()) {
             event.localRedactionEvent().off(MatrixEventEvent.Status, this.onAssociatedStatusChanged);
@@ -107,6 +118,7 @@ export default class EditHistoryMessage extends React.PureComponent<IProps, ISta
 
     public componentDidUpdate(): void {
         this.pillifyLinks();
+        this.tooltipifyLinks();
     }
 
     private renderActionBar(): JSX.Element {

src/components/views/messages/TextualBody.tsx

@@ -29,6 +29,7 @@ import * as ContextMenu from '../../structures/ContextMenu';
 import { ChevronFace, toRightOf } from '../../structures/ContextMenu';
 import SettingsStore from "../../../settings/SettingsStore";
 import { pillifyLinks, unmountPills } from '../../../utils/pillify';
+import { tooltipifyLinks, unmountTooltips } from '../../../utils/tooltipify';
 import { IntegrationManagers } from "../../../integrations/IntegrationManagers";
 import { isPermalinkHost, tryTransformPermalinkToLocalHref } from "../../../utils/permalinks/Permalinks";
 import { copyPlaintext } from "../../../utils/strings";
@@ -63,6 +64,7 @@ export default class TextualBody extends React.Component<IBodyProps, IState> {
 
     private unmounted = false;
     private pills: Element[] = [];
+    private tooltips: Element[] = [];
 
     static contextType = RoomContext;
     public context!: React.ContextType<typeof RoomContext>;
@@ -91,6 +93,7 @@ export default class TextualBody extends React.Component<IBodyProps, IState> {
         // we should be pillify them here by doing the linkifying BEFORE the pillifying.
         pillifyLinks([this.contentRef.current], this.props.mxEvent, this.pills);
         HtmlUtils.linkifyElement(this.contentRef.current);
+        tooltipifyLinks([this.contentRef.current], this.pills, this.tooltips);
         this.calculateUrlPreview();
 
         if (this.props.mxEvent.getContent().format === "org.matrix.custom.html") {
@@ -283,6 +286,7 @@ export default class TextualBody extends React.Component<IBodyProps, IState> {
     componentWillUnmount() {
         this.unmounted = true;
         unmountPills(this.pills);
+        unmountTooltips(this.tooltips);
     }
 
     shouldComponentUpdate(nextProps, nextState) {

src/components/views/rooms/LinkPreviewWidget.tsx

@@ -25,6 +25,8 @@ import Modal from "../../../Modal";
 import * as ImageUtils from "../../../ImageUtils";
 import { mediaFromMxc } from "../../../customisations/Media";
 import ImageView from '../elements/ImageView';
+import LinkWithTooltip from '../elements/LinkWithTooltip';
+import PlatformPeg from '../../../PlatformPeg';
 
 interface IProps {
     link: string;
@@ -118,12 +120,19 @@ export default class LinkPreviewWidget extends React.Component<IProps> {
         // opaque string. This does not allow any HTML to be injected into the DOM.
         const description = AllHtmlEntities.decode(p["og:description"] || "");
 
+        const anchor = <a href={this.props.link} target="_blank" rel="noreferrer noopener">{ p["og:title"] }</a>;
+        const needsTooltip = PlatformPeg.get()?.needsUrlTooltips() && this.props.link !== p["og:title"].trim();
+
         return (
             <div className="mx_LinkPreviewWidget">
                 { img }
                 <div className="mx_LinkPreviewWidget_caption">
                     <div className="mx_LinkPreviewWidget_title">
-                        <a href={this.props.link} target="_blank" rel="noreferrer noopener">{ p["og:title"] }</a>
+                        { needsTooltip ? <LinkWithTooltip
+                            tooltip={new URL(this.props.link, window.location.href).toString()}
+                        >
+                            { anchor }
+                        </LinkWithTooltip> : anchor }
                         { p["og:site_name"] && <span className="mx_LinkPreviewWidget_siteName">
                             { (" - " + p["og:site_name"]) }
                         </span> }

src/utils/tooltipify.tsx

@@ -0,0 +1,85 @@
+/*
+Copyright 2022 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 from "react";
+import ReactDOM from 'react-dom';
+
+import PlatformPeg from "../PlatformPeg";
+import LinkWithTooltip from "../components/views/elements/LinkWithTooltip";
+
+/**
+ * If the platform enabled needsUrlTooltips, recurses depth-first through a DOM tree, adding tooltip previews
+ * for link elements. Otherwise, does nothing.
+ *
+ * @param {Element[]} rootNodes - a list of sibling DOM nodes to traverse to try
+ *   to add tooltips.
+ * @param {Element[]} ignoredNodes: a list of nodes to not recurse into.
+ * @param {Element[]} containers: an accumulator of the DOM nodes which contain
+ *   React components that have been mounted by this function. The initial caller
+ *   should pass in an empty array to seed the accumulator.
+ */
+export function tooltipifyLinks(rootNodes: ArrayLike<Element>, ignoredNodes: Element[], containers: Element[]) {
+    if (!PlatformPeg.get()?.needsUrlTooltips()) {
+        return;
+    }
+
+    let node = rootNodes[0];
+
+    while (node) {
+        let tooltipified = false;
+
+        if (ignoredNodes.indexOf(node) >= 0) {
+            node = node.nextSibling as Element;
+            continue;
+        }
+
+        if (node.tagName === "A" && node.getAttribute("href")
+            && node.getAttribute("href") !== node.textContent.trim()
+        ) {
+            const container = document.createElement("span");
+            const href = node.getAttribute("href");
+
+            const tooltip = <LinkWithTooltip tooltip={new URL(href, window.location.href).toString()}>
+                <span dangerouslySetInnerHTML={{ __html: node.outerHTML }} />
+            </LinkWithTooltip>;
+
+            ReactDOM.render(tooltip, container);
+            node.parentNode.replaceChild(container, node);
+            containers.push(container);
+            tooltipified = true;
+        }
+
+        if (node.childNodes?.length && !tooltipified) {
+            tooltipifyLinks(node.childNodes as NodeListOf<Element>, ignoredNodes, containers);
+        }
+
+        node = node.nextSibling as Element;
+    }
+}
+
+/**
+ * Unmount tooltip containers created by tooltipifyLinks.
+ *
+ * It's critical to call this after tooltipifyLinks, otherwise
+ * tooltips will leak.
+ *
+ * @param {Element[]} containers - array of tooltip containers to unmount
+ */
+export function unmountTooltips(containers: Element[]) {
+    for (const container of containers) {
+        ReactDOM.unmountComponentAtNode(container);
+    }
+}

test/utils/tooltipify-test.tsx

@@ -0,0 +1,58 @@
+/*
+Copyright 2022 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 from 'react';
+import { mount } from 'enzyme';
+
+import { tooltipifyLinks } from '../../src/utils/tooltipify';
+import PlatformPeg from '../../src/PlatformPeg';
+import BasePlatform from '../../src/BasePlatform';
+
+describe('tooltipify', () => {
+    jest.spyOn(PlatformPeg, 'get')
+        .mockReturnValue({ needsUrlTooltips: () => true } as unknown as BasePlatform);
+
+    it('does nothing for empty element', () => {
+        const component = mount(<div />);
+        const root = component.getDOMNode();
+        const originalHtml = root.outerHTML;
+        const containers: Element[] = [];
+        tooltipifyLinks([root], [], containers);
+        expect(containers).toHaveLength(0);
+        expect(root.outerHTML).toEqual(originalHtml);
+    });
+
+    it('wraps single anchor', () => {
+        const component = mount(<div><a href="/foo">click</a></div>);
+        const root = component.getDOMNode();
+        const containers: Element[] = [];
+        tooltipifyLinks([root], [], containers);
+        expect(containers).toHaveLength(1);
+        const anchor = root.querySelector(".mx_TextWithTooltip_target a");
+        expect(anchor?.getAttribute("href")).toEqual("/foo");
+        expect(anchor?.innerHTML).toEqual("click");
+    });
+
+    it('ignores node', () => {
+        const component = mount(<div><a href="/foo">click</a></div>);
+        const root = component.getDOMNode();
+        const originalHtml = root.outerHTML;
+        const containers: Element[] = [];
+        tooltipifyLinks([root], [root.children[0]], containers);
+        expect(containers).toHaveLength(0);
+        expect(root.outerHTML).toEqual(originalHtml);
+    });
+});