Enable HMR

src/components/App/index.tsx

@@ -11,7 +11,8 @@ import makeClassName from 'classnames';
 import log from 'loglevel';
 import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
 
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import styles from './styles.module.scss';
 import { ApiState, actions as apiActions } from '../../reducers/api';
 import {

src/components/FileTree/index.tsx

@@ -9,7 +9,8 @@ import FileTreeNode, {
   PublicProps as FileTreeNodeProps,
 } from '../FileTreeNode';
 import Loading from '../Loading';
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import {
   FileTree,
   TreeNode,

src/components/LinterProvider/index.tsx

@@ -1,7 +1,8 @@
 import * as React from 'react';
 import { connect } from 'react-redux';
 
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import {
   LinterMessageMap,
   LinterMessagesByPath,

src/components/Navbar/index.tsx

@@ -5,7 +5,8 @@ import { Link } from 'react-router-dom';
 
 import { gettext } from '../../utils';
 import LoginButton from '../LoginButton';
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import { User, selectCurrentUser, requestLogOut } from '../../reducers/users';
 import styles from './styles.module.scss';
 

src/components/VersionChooser/index.tsx

@@ -4,7 +4,8 @@ import { connect } from 'react-redux';
 import { withRouter, RouteComponentProps } from 'react-router-dom';
 
 import Loading from '../Loading';
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import VersionSelect from '../VersionSelect';
 import { VersionsMap, fetchVersionsList } from '../../reducers/versions';
 import { gettext } from '../../utils';

src/configureStore.tsx

@@ -4,7 +4,6 @@ import {
   Middleware,
   Store,
   applyMiddleware,
-  combineReducers,
   createStore,
 } from 'redux';
 import { composeWithDevTools } from 'redux-devtools-extension';
@@ -15,21 +14,7 @@ import thunk, {
   ThunkMiddleware,
 } from 'redux-thunk';
 
-import api, { ApiState } from './reducers/api';
-import errors, { ErrorsState } from './reducers/errors';
-import fileTree, { FileTreeState } from './reducers/fileTree';
-import linter, { LinterState } from './reducers/linter';
-import users, { UsersState } from './reducers/users';
-import versions, { VersionsState } from './reducers/versions';
-
-export type ApplicationState = {
-  api: ApiState;
-  errors: ErrorsState;
-  fileTree: FileTreeState;
-  linter: LinterState;
-  users: UsersState;
-  versions: VersionsState;
-};
+import createRootReducer, { ApplicationState } from './reducers';
 
 export type ThunkActionCreator<PromiseResult = void> = ThunkAction<
   Promise<PromiseResult>,
@@ -48,37 +33,37 @@ export type ConnectedReduxProps<A extends Action = AnyAction> = {
   dispatch: ThunkDispatch<A>;
 };
 
-const createRootReducer = () => {
-  return combineReducers<ApplicationState>({
-    api,
-    errors,
-    fileTree,
-    linter,
-    users,
-    versions,
-  });
-};
-
 const configureStore = (
   preloadedState?: ApplicationState,
 ): Store<ApplicationState> => {
   const allMiddleware: Middleware[] = [
     thunk as ThunkMiddleware<ApplicationState, AnyAction>,
   ];
-  let addDevTools = false;
+  const isDevelopment = process.env.NODE_ENV === 'development';
 
-  if (process.env.NODE_ENV === 'development') {
+  if (isDevelopment) {
     allMiddleware.push(createLogger());
-    addDevTools = true;
   }
 
   let middleware = applyMiddleware(...allMiddleware);
-  if (addDevTools) {
+  if (isDevelopment) {
     const composeEnhancers = composeWithDevTools({});
     middleware = composeEnhancers(middleware);
   }
 
-  return createStore(createRootReducer(), preloadedState, middleware);
+  const store = createStore(createRootReducer(), preloadedState, middleware);
+
+  if (isDevelopment) {
+    /* istanbul ignore next */
+    if (module.hot) {
+      /* istanbul ignore next */
+      module.hot.accept('./reducers', () => {
+        store.replaceReducer(createRootReducer());
+      });
+    }
+  }
+
+  return store;
 };
 
 export default configureStore;

src/index.tsx

@@ -21,11 +21,25 @@ if (authToken === process.env.REACT_APP_AUTH_TOKEN_PLACEHOLDER) {
   );
 }
 
-ReactDOM.render(
-  <Provider store={store}>
-    <BrowserRouter>
-      <App authToken={authToken} />
-    </BrowserRouter>
-  </Provider>,
-  rootElement,
-);
+const render = (AppComponent: typeof App) => {
+  ReactDOM.render(
+    <Provider store={store}>
+      <BrowserRouter>
+        <AppComponent authToken={authToken} />
+      </BrowserRouter>
+    </Provider>,
+    rootElement,
+  );
+};
+
+render(App);
+
+/* istanbul ignore next */
+if (module.hot) {
+  /* istanbul ignore next */
+  module.hot.accept('./components/App', () => {
+    // eslint-disable-next-line global-require
+    const NextApp = require('./components/App').default;
+    render(NextApp);
+  });
+}

src/pages/Browse/index.tsx

@@ -4,7 +4,8 @@ import { connect } from 'react-redux';
 import { Col, Row } from 'react-bootstrap';
 import log from 'loglevel';
 
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import { ApiState } from '../../reducers/api';
 import FileTree from '../../components/FileTree';
 import {

src/pages/Compare/index.tsx

@@ -3,7 +3,8 @@ import { Col, Row } from 'react-bootstrap';
 import { RouteComponentProps } from 'react-router-dom';
 import { connect } from 'react-redux';
 
-import { ApplicationState, ConnectedReduxProps } from '../../configureStore';
+import { ApplicationState } from '../../reducers';
+import { ConnectedReduxProps } from '../../configureStore';
 import FileTree from '../../components/FileTree';
 import DiffView from '../../components/DiffView';
 import Loading from '../../components/Loading';

src/reducers/index.tsx

@@ -0,0 +1,30 @@
+import { combineReducers } from 'redux';
+
+import api, { ApiState } from './api';
+import errors, { ErrorsState } from './errors';
+import fileTree, { FileTreeState } from './fileTree';
+import linter, { LinterState } from './linter';
+import users, { UsersState } from './users';
+import versions, { VersionsState } from './versions';
+
+export type ApplicationState = {
+  api: ApiState;
+  errors: ErrorsState;
+  fileTree: FileTreeState;
+  linter: LinterState;
+  users: UsersState;
+  versions: VersionsState;
+};
+
+const createRootReducer = () => {
+  return combineReducers<ApplicationState>({
+    api,
+    errors,
+    fileTree,
+    linter,
+    users,
+    versions,
+  });
+};
+
+export default createRootReducer;

src/test-helpers.tsx

@@ -4,10 +4,8 @@ import { ShallowWrapper, shallow } from 'enzyme';
 import { Store } from 'redux';
 import log from 'loglevel';
 
-import configureStore, {
-  ApplicationState,
-  ThunkActionCreator,
-} from './configureStore';
+import configureStore, { ThunkActionCreator } from './configureStore';
+import { ApplicationState } from './reducers';
 import {
   ExternalLinterResult,
   ExternalLinterMessage,