[Tool] [Code Excerpt] allow excerpts in example readme (flutter#3758)

Adds the ability to add code excerpts to README files within the example directory.

script/tool/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.13.4+4
+
+* Allows code excerpts in `example/README.md`.
+
 ## 0.13.4+3
 
 * Moves source to flutter/packages.

script/tool/lib/src/update_excerpts_command.dart

@@ -89,6 +89,10 @@ class UpdateExcerptsCommand extends PackageLoopingCommand {
         if (!await _injectSnippets(example, targetPackage: package)) {
           return PackageResult.fail(<String>['Unable to inject excerpts']);
         }
+        if (!await _injectSnippets(example, targetPackage: example)) {
+          return PackageResult.fail(
+              <String>['Unable to inject example excerpts']);
+        }
       } finally {
         // Clean up the pubspec changes and extracted excerpts directory.
         _undoPubspecChanges(example);

script/tool/pubspec.yaml

@@ -1,7 +1,7 @@
 name: flutter_plugin_tools
 description: Productivity and CI utils for flutter/packages
 repository: https://github.com/flutter/packages/tree/main/script/tool
-version: 0.13.4+3
+version: 0.13.4+4
 
 dependencies:
   args: ^2.1.0

script/tool/test/update_excerpts_command_test.dart

@@ -109,6 +109,50 @@ void main() {
         ]));
   });
 
+  test('updates example readme when config is present', () async {
+    final RepositoryPackage package = createFakePlugin('a_package', packagesDir,
+        extraFiles: <String>[kReadmeExcerptConfigPath]);
+    final Directory example = getExampleDir(package);
+
+    final List<String> output =
+        await runCapturingPrint(runner, <String>['update-excerpts']);
+
+    expect(
+        processRunner.recordedCalls,
+        containsAll(<ProcessCall>[
+          ProcessCall(
+              'dart',
+              const <String>[
+                'run',
+                'build_runner',
+                'build',
+                '--config',
+                'excerpt',
+                '--output',
+                'excerpts',
+                '--delete-conflicting-outputs',
+              ],
+              example.path),
+          ProcessCall(
+              'dart',
+              const <String>[
+                'run',
+                'code_excerpt_updater',
+                '--write-in-place',
+                '--yaml',
+                '--no-escape-ng-interpolation',
+                'README.md',
+              ],
+              example.path),
+        ]));
+
+    expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('Ran for 1 package(s)'),
+        ]));
+  });
+
   test('skips when no config is present', () async {
     createFakePlugin('a_package', packagesDir);
 
@@ -231,6 +275,34 @@ void main() {
         ]));
   });
 
+  test('fails if example injection fails', () async {
+    createFakePlugin('a_package', packagesDir,
+        extraFiles: <String>[kReadmeExcerptConfigPath]);
+
+    processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+      FakeProcessInfo(MockProcess(), <String>['pub', 'get']),
+      FakeProcessInfo(MockProcess(), <String>['run', 'build_runner']),
+      FakeProcessInfo(MockProcess(), <String>['run', 'code_excerpt_updater']),
+      FakeProcessInfo(
+          MockProcess(exitCode: 1), <String>['run', 'code_excerpt_updater']),
+    ];
+
+    Error? commandError;
+    final List<String> output = await runCapturingPrint(
+        runner, <String>['update-excerpts'], errorHandler: (Error e) {
+      commandError = e;
+    });
+
+    expect(commandError, isA<ToolExit>());
+    expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('The following packages had errors:'),
+          contains('a_package:\n'
+              '    Unable to inject example excerpts')
+        ]));
+  });
+
   test('fails if READMEs are changed with --fail-on-change', () async {
     createFakePlugin('a_plugin', packagesDir,
         extraFiles: <String>[kReadmeExcerptConfigPath]);