Change to the recommended way of doing login-guarded pages.

It's also much cleaner in our case because the signup page is no longer
handled from inside the login page.

src/App.tsx

@@ -27,7 +27,6 @@ import { List, ListItem } from "./widgets/List";
 import withSpin from "./widgets/withSpin";
 import ErrorBoundary from "./components/ErrorBoundary";
 import SideMenu from "./SideMenu";
-import LoginGate from "./LoginGate";
 import { RouteResolver } from "./routes";
 
 import * as store from "./store";
@@ -35,6 +34,7 @@ import * as actions from "./store/actions";
 
 import { useCredentials } from "./credentials";
 import { SyncManager } from "./sync/SyncManager";
+import MainRouter from "./MainRouter";
 
 export const routeResolver = new RouteResolver({
   home: "",
@@ -85,6 +85,8 @@ export const routeResolver = new RouteResolver({
     new: "new",
     import: "import",
   },
+  login: {
+  },
   signup: {
   },
   settings: {
@@ -239,7 +241,7 @@ export default function App() {
           </Drawer>
 
           <ErrorBoundary>
-            <LoginGate />
+            <MainRouter />
           </ErrorBoundary>
         </div>
       </BrowserRouter>

src/LoginPage.tsx

@@ -7,7 +7,6 @@ import { useDispatch } from "react-redux";
 
 import Container from "./widgets/Container";
 import ExternalLink from "./widgets/ExternalLink";
-import SyncGate from "./SyncGate";
 import LoginForm from "./components/LoginForm";
 
 import { login } from "./store/actions";
@@ -20,18 +19,30 @@ import SignedPagesBadge from "./images/signed-pages-badge.svg";
 import { useCredentials } from "./credentials";
 import LoadingIndicator from "./widgets/LoadingIndicator";
 import { startTask } from "./helpers";
-import { Switch, Route } from "react-router";
+import { Redirect, useLocation } from "react-router";
 import { routeResolver } from "./App";
-import SignupPage from "./SignupPage";
 import { Link } from "react-router-dom";
 
+interface LocationState {
+  from: {
+    pathname: string;
+  };
+}
 
-export default function LoginGate() {
+export default function LoginPage() {
   const credentials = useCredentials();
   const dispatch = useDispatch();
+  const location = useLocation();
   const [loading, setLoading] = React.useState(false);
   const [fetchError, setFetchError] = React.useState<Error>();
 
+  const { from } = location.state as LocationState || { from: { pathname: routeResolver.getRoute("home") } };
+  if (credentials) {
+    return (
+      <Redirect to={from.pathname} />
+    );
+  }
+
   async function onFormSubmit(username: string, password: string, serviceApiUrl?: string) {
     try {
       setLoading(true);
@@ -56,7 +67,7 @@ export default function LoginGate() {
     return (
       <LoadingIndicator />
     );
-  } else if (credentials === null) {
+  } else {
     const style = {
       isSafe: {
         textDecoration: "none",
@@ -69,15 +80,6 @@ export default function LoginGate() {
     };
 
     return (
-      <Switch>
-        <Route
-          path={routeResolver.getRoute("signup")}
-          exact
-          render={() => (
-            <SignupPage />
-          )}
-        />
-        <Route>
       <Container style={{ maxWidth: "30rem" }}>
         <h2 style={{ marginBottom: "0.1em" }}>Log In</h2>
         <div style={{ fontSize: "90%" }}>or <Link to={routeResolver.getRoute("signup")}>create an account</Link></div>
@@ -100,12 +102,6 @@ export default function LoginGate() {
           <li><ExternalLink style={style.isSafe} href={C.sourceCode}>Source code</ExternalLink></li>
         </ul>
       </Container>
-        </Route>
-      </Switch>
     );
   }
-
-  return (
-    <SyncGate />
-  );
 }

src/MainRouter.tsx

@@ -0,0 +1,63 @@
+// SPDX-FileCopyrightText: © 2017 EteSync Authors
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as React from "react";
+import { Route, Switch, Redirect, RouteProps } from "react-router";
+import { useCredentials } from "./credentials";
+import LoadingIndicator from "./widgets/LoadingIndicator";
+import SyncGate from "./SyncGate";
+import { routeResolver } from "./App";
+import SignupPage from "./SignupPage";
+import LoginPage from "./LoginPage";
+
+
+export default function MainRouter() {
+  return (
+    <Switch>
+      <Route
+        path={routeResolver.getRoute("signup")}
+        exact
+      >
+        <SignupPage />
+      </Route>
+      <Route
+        path={routeResolver.getRoute("login")}
+        exact
+      >
+        <LoginPage />
+      </Route>
+      <PrivateRoute
+        path="*"
+      >
+        <SyncGate />
+      </PrivateRoute>
+    </Switch>
+  );
+}
+
+function PrivateRoute(props: Omit<RouteProps, "render">) {
+  const credentials = useCredentials();
+  const { children, ...rest } = props;
+
+  if (credentials === undefined) {
+    return (<LoadingIndicator style={{ display: "block", margin: "40px auto" }} />);
+  }
+
+  return (
+    <Route
+      {...rest}
+      render={({ location }) => (
+        (credentials) ? (
+          children
+        ) : (
+          <Redirect
+            to={{
+              pathname: "/login",
+              state: { from: location },
+            }}
+          />
+        )
+      )}
+    />
+  );
+}