Some more PR tweaks.

Author: ditman

packages/google_sign_in/google_sign_in_web/README.md

@@ -2,7 +2,7 @@
 
 The web implementation of [google_sign_in](https://pub.dev/packages/google_sign_in)
 
-## Migrating to v0.11 (Google Identity Services)
+## Migrating to v0.11 and v0.12 (Google Identity Services)
 
 The `google_sign_in_web` plugin is backed by the new Google Identity Services
 (GIS) JS SDK since version 0.11.0.
@@ -27,12 +27,12 @@ quickly and easily sign users into your app suing their Google accounts.
     flows will not return authentication information.
 * The GIS SDK no longer has direct access to previously-seen users upon initialization.
   * `signInSilently` now displays the One Tap UX for web.
-* The GIS SDK only provides an `idToken` (JWT-encoded info) when the user
-  successfully completes an authentication flow.
+* **Since 0.12** The plugin provides an `idToken` (JWT-encoded info) when the
+  user successfully completes an authentication flow:
   * In the plugin: `signInSilently` and through the web-only `renderButton` widget.
 * The plugin `signIn` method uses the Oauth "Implicit Flow" to Authorize the requested `scopes`.
   * This method only provides an `accessToken`, and not an `idToken`, so if your
-    app needs an `idToken`, this method **should be avoided**.
+    app needs an `idToken`, this method **should be avoided on the web**.
 * The GIS SDK no longer handles sign-in state and user sessions, it only provides
   Authentication credentials for the moment the user did authenticate.
 * The GIS SDK no longer is able to renew Authorization sessions on the web.
@@ -73,24 +73,24 @@ for a simple implementation of this (look at the `isAuthorized` variable).)_
 Only if the scopes required by an App are different from the
 [OpenID Connect scopes](https://developers.google.com/identity/protocols/oauth2/scopes#openid-connect).
 
-If an App only needs an `idToken`, or the OpenID Connect scopes, the "Sign In"
+If an App only needs an `idToken`, or the OpenID Connect scopes, the Authentication
 bits of the plugin should be enough for your app (`signInSilently` and `renderButton`).
 
 #### What happened to the `signIn` method on the web?
 
 Because the GIS SDK for web no longer provides users with the ability to create
 their own Sign-In buttons, or an API to start the sign in flow, the current
-implementation of `signIn` (that does authorization and authentication) is impossible
-to implement on the web.
+implementation of `signIn` (that does authorization and authentication) is no
+longer feasible on the web.
 
 The web plugin attempts to simulate the old `signIn` behavior by using the 
 [Oauth Implicit pop-up flow](https://developers.google.com/identity/oauth2/web/guides/use-token-model), which authenticates and authorizes users.
 
 The drawback of this approach is that the Oauth flow **only returns an `accessToken`**,
 and a synthetic version of the User Data, that does **not include an `idToken`**.
 
-The solution to this is to migrate your custom "Sign In" buttons in the web to
-the Button Widget provided by this package: `Widget renderButton`.
+The solution to this is to **migrate your custom "Sign In" buttons in the web to
+the Button Widget provided by this package: `Widget renderButton()`.**
 
 _(Check the [package:google_sign_in example app](https://pub.dev/packages/google_sign_in/example)
 for an example on how to mix the `renderButton` widget on the web, with a custom
@@ -152,6 +152,9 @@ so you do not need to add it to your `pubspec.yaml`.
 However, if you `import` this package to use any of its APIs directly, you
 should add it to your `pubspec.yaml` as usual.
 
+For example, you need to import this package directly if you plan to use the
+web-only `Widget renderButton()` method.
+
 ### Web integration
 
 First, go through the instructions [here](https://developers.google.com/identity/gsi/web/guides/get-google-api-clientid) to create your Google Sign-In OAuth client ID.

packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart

@@ -54,7 +54,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
     @visibleForTesting
         StreamController<GoogleSignInUserData?>?
             debugOverrideUserDataController,
-  })  : _gisClient = debugOverrideGisSdkClient,
+  })  : _gisSdkClient = debugOverrideGisSdkClient,
         _userDataController = debugOverrideUserDataController ??
             StreamController<GoogleSignInUserData?>.broadcast() {
     autoDetectedClientId = html
@@ -81,7 +81,17 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   final StreamController<GoogleSignInUserData?> _userDataController;
 
   // The instance of [GisSdkClient] backing the plugin.
-  GisSdkClient? _gisClient;
+  GisSdkClient? _gisSdkClient;
+
+  // A convenience getter to avoid using ! when accessing _gisSdkClient, and
+  // providing a slightly better error message when it is Null.
+  GisSdkClient get _gisClient {
+    assert(_gisSdkClient != null, 'GIS Client not initialized. '
+      'GoogleSignInPlugin::init() or GoogleSignInPlugin::initWithParams() '
+      'must be called before any other method in this plugin.',
+    );
+    return _gisSdkClient!;
+  }
 
   // This method throws if init or initWithParams hasn't been called at some
   // point in the past. It is used by the [initialized] getter to ensure that
@@ -152,7 +162,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
 
     await _jsSdkLoadedFuture;
 
-    _gisClient ??= GisSdkClient(
+    _gisSdkClient ??= GisSdkClient(
       clientId: appClientId!,
       hostedDomain: params.hostedDomain,
       initialScopes: List<String>.from(params.scopes),
@@ -194,7 +204,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
                     domDocument.querySelector('#sign_in_button_$viewId');
                 assert(element != null,
                     'Cannot render GSI button. DOM is not ready!');
-                _gisClient!.renderButton(element!, config);
+                _gisClient.renderButton(element!, config);
               });
         }
         return const Text('Getting ready');
@@ -207,7 +217,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
     await initialized;
 
     // The new user is being injected from the `userDataEvents` Stream.
-    return _gisClient!.signInSilently();
+    return _gisClient.signInSilently();
   }
 
   @override
@@ -221,7 +231,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
     // This method will synthesize authentication information from the People API
     // if needed (or use the last identity seen from signInSilently).
     try {
-      return _gisClient!.signIn();
+      return _gisClient.signIn();
     } catch (reason) {
       throw PlatformException(
         code: reason.toString(),
@@ -239,50 +249,50 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   }) async {
     await initialized;
 
-    return _gisClient!.getTokens();
+    return _gisClient.getTokens();
   }
 
   @override
   Future<void> signOut() async {
     await initialized;
 
-    _gisClient!.signOut();
+    _gisClient.signOut();
   }
 
   @override
   Future<void> disconnect() async {
     await initialized;
 
-    _gisClient!.disconnect();
+    _gisClient.disconnect();
   }
 
   @override
   Future<bool> isSignedIn() async {
     await initialized;
 
-    return _gisClient!.isSignedIn();
+    return _gisClient.isSignedIn();
   }
 
   @override
   Future<void> clearAuthCache({required String token}) async {
     await initialized;
 
-    _gisClient!.clearAuthCache();
+    _gisClient.clearAuthCache();
   }
 
   @override
   Future<bool> requestScopes(List<String> scopes) async {
     await initialized;
 
-    return _gisClient!.requestScopes(scopes);
+    return _gisClient.requestScopes(scopes);
   }
 
   @override
   Future<bool> canAccessScopes(List<String> scopes,
       {String? accessToken}) async {
     await initialized;
 
-    return _gisClient!.canAccessScopes(scopes, accessToken);
+    return _gisClient.canAccessScopes(scopes, accessToken);
   }
 
   @override