redux [nfc]: Set up a GlobalThunkExtras

This doesn't yet do anything, but it provides the vessel
through which we can start providing extras here.

Co-authored-by: Chris Bobbe <[email protected]>

Author: gnprice

src/boot/store.js

@@ -20,6 +20,7 @@ import CompressedAsyncStorage from '../storage/CompressedAsyncStorage';
 import createMigration from '../redux-persist-migrate/index';
 import { getGlobalSession, getGlobalSettings } from '../directSelectors';
 import { migrations } from '../storage/migrations';
+import type { GlobalThunkExtras } from '../reduxTypes';
 
 if (process.env.NODE_ENV === 'development') {
   // Chrome dev tools for Immutable.
@@ -72,14 +73,23 @@ export const cacheKeys: $ReadOnlyArray<$Keys<GlobalState>> = [
   'realm', 'streams', 'subscriptions', 'unread', 'userGroups', 'users',
 ];
 
-const thunkExtras: ThunkExtras = {
+const thunkExtras: $Exact<ThunkExtras> = {
   // eslint-disable-next-line no-use-before-define
   getGlobalSession: () => getGlobalSession(store.getState()),
 
   // eslint-disable-next-line no-use-before-define
   getGlobalSettings: () => getGlobalSettings(store.getState()),
 };
 
+const globalThunkExtras: $Exact<GlobalThunkExtras> = Object.freeze({
+  // TODO add things
+});
+
+const combinedThunkExtras: ThunkExtras & GlobalThunkExtras = {
+  ...thunkExtras,
+  ...globalThunkExtras,
+};
+
 /**
  * Return a list of Redux middleware objects to use in our Redux store.
  *
@@ -97,7 +107,7 @@ function listMiddleware() {
     // Handle the fancy "thunk" actions we often use, i.e. async
     // functions of `dispatch` and `state`.  See docs:
     //   https://github.com/reduxjs/redux-thunk
-    thunkMiddleware.withExtraArgument(thunkExtras),
+    thunkMiddleware.withExtraArgument(combinedThunkExtras),
   ];
 
   if (config.enableReduxLogging) {

src/reduxTypes.js

@@ -636,21 +636,26 @@ export interface Dispatch {
 /** A per-account thunk action returning T. */
 export type ThunkAction<T> = (Dispatch, () => PerAccountState, ThunkExtras) => T;
 
+/** The extras object passed to a global thunk action. */
+export type GlobalThunkExtras = $ReadOnly<{
+  // TODO add things
+  ...
+}>;
+
 /** The Redux `dispatch` for a global context. */
 export interface GlobalDispatch {
   <A: DispatchableWithoutAccountAction>(action: A): A;
   <T>(GlobalThunkAction<T>): T;
 }
 
 /** A global thunk action returning T. */
-// This might take some extras later (e.g., to do something per-account on a
-// specific account), but for now it needs none.
-export type GlobalThunkAction<T> = (GlobalDispatch, () => GlobalState) => T;
+export type GlobalThunkAction<T> = (GlobalDispatch, () => GlobalState, GlobalThunkExtras) => T;
 
 // The two pairs of dispatch/thunk-action types aren't interchangeable,
 // in either direction.
 //   $FlowExpectedError[incompatible-return]
 (d: GlobalDispatch): Dispatch => d;
+//   $FlowExpectedError[prop-missing]
 //   $FlowExpectedError[incompatible-return]
 <T>(a: ThunkAction<T>): GlobalThunkAction<T> => a;
 //   $FlowExpectedError[incompatible-return]