Add customisation point for visibility of invites and room creation

Fixes https://github.com/vector-im/element-web/issues/19331

src/customisations/ComponentVisibility.ts

@@ -0,0 +1,51 @@
+/*
+Copyright 2021 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.
+*/
+
+// Dev note: this customisation point is heavily inspired by UIFeature flags, though
+// with an intention of being used for more complex switching on whether or not a feature
+// should be shown.
+
+// Populate this class with the details of your customisations when copying it.
+
+import { UIComponent } from "../settings/UIFeature";
+
+/**
+ * Determines whether or not the active MatrixClient user should be able to use
+ * the given UI component. If shown, the user might still not be able to use the
+ * component depending on their contextual permissions. For example, invite options
+ * might be shown to the user but they won't have permission to invite users to
+ * the current room: the button will appear disabled.
+ * @param {UIComponent} component The component to check visibility for.
+ * @returns {boolean} True (default) if the user is able to see the component, false
+ * otherwise.
+ */
+function shouldShowComponent(component: UIComponent): boolean {
+    return true; // default to visible
+}
+
+// This interface summarises all available customisation points and also marks
+// them all as optional. This allows customisers to only define and export the
+// customisations they need while still maintaining type safety.
+export interface IComponentVisibilityCustomisations {
+    shouldShowComponent?: typeof shouldShowComponent;
+}
+
+// A real customisation module will define and export one or more of the
+// customisation points that make up the interface above.
+export const ComponentVisibilityCustomisations: IComponentVisibilityCustomisations = {
+    // while we don't specify the functions here, their defaults are described
+    // in their pseudo-implementations above.
+};