Support semi-perma-disabling of lab features

Adding `override: true` will remove the feature from the labs section, and force Riot to always use the default value (i.e. ignoring localStorage). This is useful removing features entirely when they might be deliberately not working but we still want to do a release.

src/UserSettingsStore.js

@@ -171,22 +171,36 @@ export default {
         localStorage.setItem('mx_local_settings', JSON.stringify(settings));
     },
 
-    isFeatureEnabled: function(feature: string): boolean {
+    getFeatureById(feature: string) {
+        for (let i = 0; i < this.LABS_FEATURES.length; i++) {
+            const f = this.LABS_FEATURES[i];
+            if (f.id === feature) {
+                return f;
+            }
+        }
+        return null;
+    },
+
+    isFeatureEnabled: function(featureId: string): boolean {
         // Disable labs for guests.
         if (MatrixClientPeg.get().isGuest()) return false;
 
-        if (localStorage.getItem(`mx_labs_feature_${feature}`) === null) {
-            for (let i = 0; i < this.LABS_FEATURES.length; i++) {
-                const f = this.LABS_FEATURES[i];
-                if (f.id === feature) {
-                    return f.default;
-                }
-            }
+        const feature = this.getFeatureById(featureId);
+        if (!feature) {
+            console.warn('Unknown feature');
+            return false;
         }
-        return localStorage.getItem(`mx_labs_feature_${feature}`) === 'true';
+        // Return the default if this feature has an override to be the default value or
+        // if the feature has never been toggled and is therefore not in localStorage
+        if (Object.keys(feature).includes('override') ||
+            localStorage.getItem(`mx_labs_feature_${featureId}`) === null
+        ) {
+            return feature.default;
+        }
+        return localStorage.getItem(`mx_labs_feature_${featureId}`) === 'true';
     },
 
-    setFeatureEnabled: function(feature: string, enabled: boolean) {
-        localStorage.setItem(`mx_labs_feature_${feature}`, enabled);
+    setFeatureEnabled: function(featureId: string, enabled: boolean) {
+        localStorage.setItem(`mx_labs_feature_${featureId}`, enabled);
     },
 };

src/components/structures/UserSettings.js

@@ -859,7 +859,13 @@ module.exports = React.createClass({
         if (this.props.enableLabs === false) return null;
         UserSettingsStore.doTranslations();
 
-        const features = UserSettingsStore.LABS_FEATURES.map((feature) => {
+        const features = [];
+        UserSettingsStore.LABS_FEATURES.forEach((feature) => {
+            // This feature has an override and will be set to the default, so do not
+            // show it here.
+            if (feature.override) {
+                return;
+            }
             // TODO: this ought to be a separate component so that we don't need
             // to rebind the onChange each time we render
             const onChange = (e) => {
@@ -867,7 +873,7 @@ module.exports = React.createClass({
                 this.forceUpdate();
             };
 
-            return (
+            features.push(
                 <div key={feature.id} className="mx_UserSettings_toggle">
                     <input
                         type="checkbox"
@@ -880,6 +886,12 @@ module.exports = React.createClass({
                 </div>
             );
         });
+
+        // No labs section when there are no features in labs
+        if (features.length === 0) {
+            return null;
+        }
+
         return (
             <div>
                 <h3>{ _t("Labs") }</h3>