[google_sign_in] Adopt code excerpts in README (flutter#5521)

Improves README example and updates it to use code excerpts.

Part of [flutter#102679](flutter#102679)

Author: mike-v2

packages/google_sign_in/google_sign_in/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 6.2.1
+
+* Improves README example and updates it to use code excerpts.
+
 ## 6.2.0
 
 * Adds support for macOS.

packages/google_sign_in/google_sign_in/README.md

@@ -68,27 +68,27 @@ To use this plugin, follow the
 
 ### Use the plugin
 
-Add the following import to your Dart code:
-
-```dart
-import 'package:google_sign_in/google_sign_in.dart';
-```
-
 Initialize `GoogleSignIn` with the scopes you want:
 
+<?code-excerpt "example/lib/main.dart (Initialize)"?>
 ```dart
+const List<String> scopes = <String>[
+  'email',
+  'https://www.googleapis.com/auth/contacts.readonly',
+];
+
 GoogleSignIn _googleSignIn = GoogleSignIn(
-  scopes: [
-    'email',
-    'https://www.googleapis.com/auth/contacts.readonly',
-  ],
+  // Optional clientId
+  // clientId: 'your-client_id.apps.googleusercontent.com',
+  scopes: scopes,
 );
 ```
 
 [Full list of available scopes](https://developers.google.com/identity/protocols/googlescopes).
 
 You can now use the `GoogleSignIn` class to authenticate in your Dart code, e.g.
 
+<?code-excerpt "example/lib/main.dart (SignIn)"?>
 ```dart
 Future<void> _handleSignIn() async {
   try {
@@ -122,8 +122,14 @@ Applications must be able to:
 
 There's a new method that enables the checks above, `canAccessScopes`:
 
+<?code-excerpt "example/lib/main.dart (CanAccessScopes)"?>
 ```dart
-final bool isAuthorized = await _googleSignIn.canAccessScopes(scopes);
+// In mobile, being authenticated means being authorized...
+bool isAuthorized = account != null;
+// However, on web...
+if (kIsWeb && account != null) {
+  isAuthorized = await _googleSignIn.canAccessScopes(scopes);
+}
 ```
 
 _(Only implemented in the web platform, from version 6.1.0 of this package)_
@@ -134,14 +140,13 @@ If an app determines that the user hasn't granted the scopes it requires, it
 should initiate an Authorization request. (Remember that in the web platform,
 this request **must be initiated from an user interaction**, like a button press).
 
+<?code-excerpt "example/lib/main.dart (RequestScopes)" plaster="none"?>
 ```dart
 Future<void> _handleAuthorizeScopes() async {
   final bool isAuthorized = await _googleSignIn.requestScopes(scopes);
   if (isAuthorized) {
-    // Do things that only authorized users can do!
-    _handleGetContact(_currentUser!);
+    unawaited(_handleGetContact(_currentUser!));
   }
-}
 ```
 
 The `requestScopes` returns a `boolean` value that is `true` if the user has

packages/google_sign_in/google_sign_in/example/lib/main.dart

@@ -15,6 +15,7 @@ import 'package:http/http.dart' as http;
 import 'src/sign_in_button.dart';
 
 /// The scopes required by this application.
+// #docregion Initialize
 const List<String> scopes = <String>[
   'email',
   'https://www.googleapis.com/auth/contacts.readonly',
@@ -25,6 +26,7 @@ GoogleSignIn _googleSignIn = GoogleSignIn(
   // clientId: 'your-client_id.apps.googleusercontent.com',
   scopes: scopes,
 );
+// #enddocregion Initialize
 
 void main() {
   runApp(
@@ -55,12 +57,14 @@ class _SignInDemoState extends State<SignInDemo> {
 
     _googleSignIn.onCurrentUserChanged
         .listen((GoogleSignInAccount? account) async {
+// #docregion CanAccessScopes
       // In mobile, being authenticated means being authorized...
       bool isAuthorized = account != null;
-      // However, in the web...
+      // However, on web...
       if (kIsWeb && account != null) {
         isAuthorized = await _googleSignIn.canAccessScopes(scopes);
       }
+// #enddocregion CanAccessScopes
 
       setState(() {
         _currentUser = account;
@@ -136,28 +140,34 @@ class _SignInDemoState extends State<SignInDemo> {
   //
   // On the web, the on-click handler of the Sign In button is owned by the JS
   // SDK, so this method can be considered mobile only.
+  // #docregion SignIn
   Future<void> _handleSignIn() async {
     try {
       await _googleSignIn.signIn();
     } catch (error) {
       print(error);
     }
   }
+  // #enddocregion SignIn
 
   // Prompts the user to authorize `scopes`.
   //
   // This action is **required** in platforms that don't perform Authentication
   // and Authorization at the same time (like the web).
   //
   // On the web, this must be called from an user interaction (button click).
+  // #docregion RequestScopes
   Future<void> _handleAuthorizeScopes() async {
     final bool isAuthorized = await _googleSignIn.requestScopes(scopes);
+    // #enddocregion RequestScopes
     setState(() {
       _isAuthorized = isAuthorized;
     });
+    // #docregion RequestScopes
     if (isAuthorized) {
       unawaited(_handleGetContact(_currentUser!));
     }
+    // #enddocregion RequestScopes
   }
 
   Future<void> _handleSignOut() => _googleSignIn.disconnect();

packages/google_sign_in/google_sign_in/pubspec.yaml

@@ -3,7 +3,7 @@ description: Flutter plugin for Google Sign-In, a secure authentication system
   for signing in with a Google account.
 repository: https://github.com/flutter/packages/tree/main/packages/google_sign_in/google_sign_in
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+google_sign_in%22
-version: 6.2.0
+version: 6.2.1
 
 environment:
   sdk: ">=3.2.0 <4.0.0"

script/configs/temp_exclude_excerpt.yaml

@@ -8,7 +8,6 @@
 - espresso
 - extension_google_sign_in_as_googleapis_auth
 - go_router_builder
-- google_sign_in/google_sign_in
 - image_picker_for_web
 - in_app_purchase/in_app_purchase
 - ios_platform_images