Determine type of sidebar store automatically

Avoid the need to manually create the `SidebarStore` type by inferring
it automatically. This works as follows:

 1. The `modules` argument to `createStore` has been converted to a
    tuple type (`[ModuleA, ModuleB, ...]`)
 2. The type of a module that would result from merging all the
    individual modules (`ModuleA & ModuleB ...`) is computed
    using a `TupleToIntersection` utility type
 3. `StoreFromModule` is used to compute the type of the store that the
    merged module would produce

Author: robertknight

src/sidebar/store/create-store.js

@@ -149,6 +149,24 @@ function assignOnce(target, source) {
   return Object.assign(target, source);
 }
 
+/**
+ * @template T
+ * @typedef {{[K in keyof T]: (x: T[K]) => void }} MapContravariant
+ */
+
+/**
+ * Utility that turns a tuple type `[A, B, C]` into an intersection `A & B & C`.
+ *
+ * The implementation is magic adapted from
+ * https://github.com/microsoft/TypeScript/issues/28323. Roughly speaking it
+ * works by computing a type that could be assigned to any position in the
+ * tuple, which must be the intersection of all the tuple element types.
+ *
+ * @template T
+ * @template {Record<number, unknown>} [Temp=MapContravariant<T>]
+ * @typedef {Temp[number] extends (x: infer U) => unknown ? U : never} TupleToIntersection
+ */
+
 /**
  * Create a Redux store from a set of _modules_.
  *
@@ -173,10 +191,11 @@ function assignOnce(target, source) {
  * `use-store.js`. This returns a proxy which enables UI components to observe
  * what store state a component depends upon and re-render when it changes.
  *
- * @param {Module<any,any,any,any>[]} modules
+ * @template {readonly Module<any,any,any,any>[]} Modules
+ * @param {Modules} modules
  * @param {any[]} [initArgs] - Arguments to pass to each state module's `initialState` function
  * @param {any[]} [middleware] - List of additional Redux middlewares to use
- * @return Store<any,any,any>
+ * @return {StoreFromModule<TupleToIntersection<Modules>>}
  */
 export function createStore(modules, initArgs = [], middleware = []) {
   /** @type {Record<string, unknown>} */
@@ -241,7 +260,7 @@ export function createStore(modules, initArgs = [], middleware = []) {
   }
   Object.assign(store, selectorMethods);
 
-  return store;
+  return /** @type {any} */ (store);
 }
 
 /**

src/sidebar/store/index.js

@@ -17,30 +17,7 @@ import { sidebarPanelsModule } from './modules/sidebar-panels';
 import { toastMessagesModule } from './modules/toast-messages';
 import { viewerModule } from './modules/viewer';
 
-/**
- * @template M
- * @typedef {import('./create-store').StoreFromModule<M>} StoreFromModule
- */
-
-/**
- * @typedef {StoreFromModule<activityModule> &
- *   StoreFromModule<annotationsModule> &
- *   StoreFromModule<defaultsModule> &
- *   StoreFromModule<directLinkedModule> &
- *   StoreFromModule<draftsModule> &
- *   StoreFromModule<filtersModule> &
- *   StoreFromModule<framesModule> &
- *   StoreFromModule<groupsModule> &
- *   StoreFromModule<linksModule> &
- *   StoreFromModule<realTimeUpdatesModule> &
- *   StoreFromModule<routeModule> &
- *   StoreFromModule<selectionModule> &
- *   StoreFromModule<sessionModule> &
- *   StoreFromModule<sidebarPanelsModule> &
- *   StoreFromModule<toastMessagesModule> &
- *   StoreFromModule<viewerModule>
- *  } SidebarStore
- */
+/** @typedef {ReturnType<createSidebarStore>} SidebarStore */
 
 /**
  * Create the central state store for the sidebar application.
@@ -52,13 +29,14 @@ import { viewerModule } from './modules/viewer';
  * [1] https://redux.js.org
  *
  * @param {import('../../types/config').SidebarSettings} settings
- * @return {SidebarStore}
  * @inject
  */
 export function createSidebarStore(settings) {
   const middleware = [debugMiddleware];
 
-  const modules = [
+  // `const` type gives `modules` a tuple type, which allows `createStore`
+  // to infer properties (eg. action and selector methods) of returned store.
+  const modules = /** @type {const} */ ([
     activityModule,
     annotationsModule,
     defaultsModule,
@@ -75,8 +53,6 @@ export function createSidebarStore(settings) {
     sidebarPanelsModule,
     toastMessagesModule,
     viewerModule,
-  ];
-  return /** @type {SidebarStore} */ (
-    createStore(modules, [settings], middleware)
-  );
+  ]);
+  return createStore(modules, [settings], middleware);
 }