Introduce a concept of UI features, using it for URL previews at first

Fixes https://github.com/vector-im/element-web/issues/15176

This is effectively the base for all of https://github.com/vector-im/element-web/issues/15185

docs/settings.md

@@ -120,6 +120,18 @@ Call `SettingsStore.getValue()` as you would for any other setting.
 
 Call `SettingsStore.setValue("feature_name", null, SettingLevel.DEVICE, true)`.
 
+### A note on UI features
+
+UI features are a different concept to plain features. Instead of being representative of unstable or
+unpredicatable behaviour, they are logical chunks of UI which can be disabled by deployments for ease
+of understanding with users. They are simply represented as boring settings with a convention of being
+named as `UIFeature.$location` where `$location` is a rough descriptor of what is toggled, such as
+`URLPreviews` or `Communities`.
+
+UI features also tend to have their own setting controller (see below) to manipulate settings which might
+be affected by the UI feature being disabled. For example, if URL previews are disabled as a UI feature
+then the URL preview options will use the `UIFeatureController` to ensure they remain disabled while the
+UI feature is disabled.
 
 ## Setting controllers
 
@@ -226,4 +238,3 @@ In practice, handlers which rely on remote changes (account data, room events, e
 generalized `WatchManager` - a class specifically designed to deduplicate the logic of managing watchers. The handlers 
 which are localized to the local client (device) generally just trigger the `WatchManager` when they manipulate the 
 setting themselves as there's nothing to really 'watch'.
- 

src/components/views/settings/tabs/room/GeneralRoomSettingsTab.js

@@ -22,6 +22,8 @@ import * as sdk from "../../../../..";
 import AccessibleButton from "../../../elements/AccessibleButton";
 import dis from "../../../../../dispatcher/dispatcher";
 import MatrixClientContext from "../../../../../contexts/MatrixClientContext";
+import SettingsStore from "../../../../../settings/SettingsStore";
+import {UIFeature} from "../../../../../settings/UIFeature";
 
 export default class GeneralRoomSettingsTab extends React.Component {
     static propTypes = {
@@ -61,6 +63,16 @@ export default class GeneralRoomSettingsTab extends React.Component {
         const canChangeGroups = room.currentState.mayClientSendStateEvent("m.room.related_groups", client);
         const groupsEvent = room.currentState.getStateEvents("m.room.related_groups", "");
 
+        let urlPreviewSettings = <>
+            <span className='mx_SettingsTab_subheading'>{_t("URL Previews")}</span>
+            <div className='mx_SettingsTab_section'>
+                <UrlPreviewSettings room={room} />
+            </div>
+        </>;
+        if (!SettingsStore.getValue(UIFeature.URLPreviews)) {
+            urlPreviewSettings = null;
+        }
+
         return (
             <div className="mx_SettingsTab mx_GeneralRoomSettingsTab">
                 <div className="mx_SettingsTab_heading">{_t("General")}</div>
@@ -82,10 +94,7 @@ export default class GeneralRoomSettingsTab extends React.Component {
                                           relatedGroupsEvent={groupsEvent} />
                 </div>
 
-                <span className='mx_SettingsTab_subheading'>{_t("URL Previews")}</span>
-                <div className='mx_SettingsTab_section'>
-                    <UrlPreviewSettings room={room} />
-                </div>
+                {urlPreviewSettings}
 
                 <span className='mx_SettingsTab_subheading'>{_t("Leave room")}</span>
                 <div className='mx_SettingsTab_section'>

src/components/views/settings/tabs/user/PreferencesUserSettingsTab.js

@@ -23,6 +23,7 @@ import Field from "../../../elements/Field";
 import * as sdk from "../../../../..";
 import PlatformPeg from "../../../../../PlatformPeg";
 import {SettingLevel} from "../../../../../settings/SettingLevel";
+import {UIFeature} from "../../../../../settings/UIFeature";
 
 export default class PreferencesUserSettingsTab extends React.Component {
     static ROOM_LIST_SETTINGS = [
@@ -138,6 +139,10 @@ export default class PreferencesUserSettingsTab extends React.Component {
     };
 
     _renderGroup(settingIds) {
+        if (!SettingsStore.getValue(UIFeature.URLPreviews)) {
+            settingIds = settingIds.filter(i => i !== 'urlPreviewsEnabled');
+        }
+
         const SettingsFlag = sdk.getComponent("views.elements.SettingsFlag");
         return settingIds.map(i => <SettingsFlag key={i} name={i} level={SettingLevel.ACCOUNT} />);
     }

src/i18n/strings/en_EN.json

@@ -946,8 +946,8 @@
     "This room is bridging messages to the following platforms. <a>Learn more.</a>": "This room is bridging messages to the following platforms. <a>Learn more.</a>",
     "This room isn’t bridging messages to any platforms. <a>Learn more.</a>": "This room isn’t bridging messages to any platforms. <a>Learn more.</a>",
     "Bridges": "Bridges",
-    "Room Addresses": "Room Addresses",
     "URL Previews": "URL Previews",
+    "Room Addresses": "Room Addresses",
     "Uploaded sound": "Uploaded sound",
     "Sounds": "Sounds",
     "Notification sound": "Notification sound",

src/settings/Settings.ts

@@ -32,6 +32,8 @@ import UseSystemFontController from './controllers/UseSystemFontController';
 import { SettingLevel } from "./SettingLevel";
 import SettingController from "./controllers/SettingController";
 import { RightPanelPhases } from "../stores/RightPanelStorePhases";
+import UIFeatureController from "./controllers/UIFeatureController";
+import { UIFeature } from "./UIFeature";
 
 // These are just a bunch of helper arrays to avoid copy/pasting a bunch of times
 const LEVELS_ROOM_SETTINGS = [
@@ -69,6 +71,10 @@ const LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG = [
     SettingLevel.DEVICE,
     SettingLevel.CONFIG,
 ];
+const LEVELS_UI_FEATURE = [
+    SettingLevel.CONFIG,
+    // in future we might have a .well-known level or something
+];
 
 export interface ISetting {
     // Must be set to true for features. Default is 'false'.
@@ -447,6 +453,7 @@ export const SETTINGS: {[setting: string]: ISetting} = {
             "room": _td("Enable URL previews by default for participants in this room"),
         },
         default: true,
+        controller: new UIFeatureController(UIFeature.URLPreviews),
     },
     "urlPreviewsEnabled_e2ee": {
         supportedLevels: [SettingLevel.ROOM_DEVICE, SettingLevel.ROOM_ACCOUNT],
@@ -454,6 +461,7 @@ export const SETTINGS: {[setting: string]: ISetting} = {
             "room-account": _td("Enable URL previews for this room (only affects you)"),
         },
         default: false,
+        controller: new UIFeatureController(UIFeature.URLPreviews),
     },
     "roomColor": {
         supportedLevels: LEVELS_ROOM_SETTINGS_WITH_ROOM,
@@ -611,4 +619,8 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         supportedLevels: LEVELS_ROOM_OR_ACCOUNT,
         default: {},
     },
+    [UIFeature.URLPreviews]: {
+        supportedLevels: LEVELS_UI_FEATURE,
+        default: true,
+    },
 };

src/settings/UIFeature.ts

@@ -0,0 +1,20 @@
+/*
+Copyright 2020 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.
+*/
+
+// see settings.md for documentation on conventions
+export enum UIFeature {
+    URLPreviews = "UIFeature.URLPreviews",
+}

src/settings/controllers/UIFeatureController.ts

@@ -0,0 +1,45 @@
+/*
+Copyright 2020 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 SettingController from "./SettingController";
+import { SettingLevel } from "../SettingLevel";
+import SettingsStore from "../SettingsStore";
+
+/**
+ * Enforces that a boolean setting cannot be enabled if the corresponding
+ * UI feature is disabled. If the UI feature is enabled, the setting value
+ * is unchanged.
+ *
+ * Settings using this controller are assumed to return `false` when disabled.
+ */
+export default class UIFeatureController extends SettingController {
+    public constructor(private uiFeatureName: string) {
+        super();
+    }
+
+    public getValueOverride(
+        level: SettingLevel,
+        roomId: string,
+        calculatedValue: any,
+        calculatedAtLevel: SettingLevel,
+    ): any {
+        if (!SettingsStore.getValue(this.uiFeatureName)) {
+            // per the docs: we force a disabled state when the feature isn't active
+            return false;
+        }
+        return null; // no override
+    }
+}