Analyze dartpad (#45124)

This fixes the sample code analysis to treat dartpad snippets in the same way as snippet snippets, which it wasn't until now (the snippet generator was treating them as "samples"), and some errors crept in. This PR also fixes those errors.

Also, added a --verbose option to the sample analyzer.

dev/bots/analyze-sample-code.dart

@@ -63,6 +63,12 @@ void main(List<String> arguments) {
         'directory in the system temp folder. If specified, will not be '
         'automatically removed at the end of execution.',
   );
+  argParser.addFlag(
+    'verbose',
+    defaultsTo: false,
+    negatable: false,
+    help: 'Print verbose output for the analysis process.',
+  );
   argParser.addFlag(
     'help',
     defaultsTo: false,
@@ -100,7 +106,7 @@ void main(List<String> arguments) {
     tempDirectory.createSync();
   }
   try {
-    exitCode = SampleChecker(flutterPackage, tempDirectory: tempDirectory).checkSamples();
+    exitCode = SampleChecker(flutterPackage, tempDirectory: tempDirectory, verbose: parsedArguments['verbose']).checkSamples();
   } on SampleCheckerException catch (e) {
     stderr.write(e);
     exit(1);
@@ -140,7 +146,7 @@ class SampleCheckerException implements Exception {
 /// don't necessarily match. It does, however, print the source of the
 /// problematic line.
 class SampleChecker {
-  SampleChecker(this._flutterPackage, {Directory tempDirectory})
+  SampleChecker(this._flutterPackage, {Directory tempDirectory, this.verbose = false})
       : _tempDirectory = tempDirectory,
         _keepTmp = tempDirectory != null {
     _tempDirectory ??= Directory.systemTemp.createTempSync('flutter_analyze_sample_code.');
@@ -153,7 +159,7 @@ class SampleChecker {
   static const String _dartDocPrefixWithSpace = '$_dartDocPrefix ';
 
   /// A RegExp that matches the beginning of a dartdoc snippet or sample.
-  static final RegExp _dartDocSampleBeginRegex = RegExp(r'{@tool (sample|snippet)(?:| ([^}]*))}');
+  static final RegExp _dartDocSampleBeginRegex = RegExp(r'{@tool (sample|snippet|dartpad)(?:| ([^}]*))}');
 
   /// A RegExp that matches the end of a dartdoc snippet or sample.
   static final RegExp _dartDocSampleEndRegex = RegExp(r'{@end-tool}');
@@ -167,6 +173,9 @@ class SampleChecker {
   /// A RegExp that matches a Dart constructor.
   static final RegExp _constructorRegExp = RegExp(r'(const\s+)?_*[A-Z][a-zA-Z0-9<>._]*\(');
 
+  /// Whether or not to print verbose output.
+  final bool verbose;
+
   /// Whether or not to keep the temp directory around after running.
   ///
   /// Defaults to false.
@@ -313,6 +322,9 @@ class SampleChecker {
     ];
     print('Generating snippet for ${snippet.start?.filename}:${snippet.start?.line}');
     final ProcessResult process = _runSnippetsScript(args);
+    if (verbose) {
+      stderr.write('${process.stderr}');
+    }
     if (process.exitCode != 0) {
       throw SampleCheckerException(
         'Unable to create snippet for ${snippet.start.filename}:${snippet.start.line} '
@@ -427,7 +439,7 @@ class SampleChecker {
             startLine = Line('', filename: relativeFilePath, line: lineNumber + 1, indent: 3);
             inPreamble = true;
           } else if (sampleMatch != null) {
-            inSnippet = sampleMatch != null && sampleMatch[1] == 'snippet';
+            inSnippet = sampleMatch != null && (sampleMatch[1] == 'snippet' || sampleMatch[1] == 'dartpad');
             if (inSnippet) {
               startLine = Line(
                 '',

dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart

@@ -34,6 +34,26 @@
 /// ```
 /// {@end-tool}
 ///
+/// {@tool dartpad --template=stateless_widget_material}
+/// Bla blabla blabla some [Text] when the `_blabla` blabla blabla is true, and
+/// blabla it when it is blabla:
+///
+/// ```dart preamble
+/// bool _visible = true;
+/// final GlobalKey globalKey = GlobalKey();
+/// ```
+///
+/// ```dart
+/// Widget build(BuildContext context) {
+///   return Opacity(
+///     key: globalKey,
+///     opacity: _visible ? 1.0 : 0.0,
+///     child: const Text('Poor wandering ones!'),
+///   );
+/// }
+/// ```
+/// {@end-tool}
+///
 /// {@tool sample}
 /// Bla blabla blabla some [Text] when the `_blabla` blabla blabla is true, and
 /// blabla finale blabla:

dev/bots/test/analyze-sample-code_test.dart

@@ -19,12 +19,17 @@ void main() {
     expect(stderrLines, <String>[
       'known_broken_documentation.dart:30:9: new Opacity(',
       '>>> Unnecessary new keyword (unnecessary_new)',
-      'known_broken_documentation.dart:42:9: new Opacity(',
+      'known_broken_documentation.dart:62:9: new Opacity(',
       '>>> Unnecessary new keyword (unnecessary_new)',
       '',
       'Found 1 sample code errors.',
       '',
     ]);
-    expect(stdoutLines, <String>['Found 7 sample code sections.', 'Starting analysis of samples.', '']);
+    expect(stdoutLines, <String>[
+      'Found 7 sample code sections.',
+      'Generating snippet for known_broken_documentation.dart:38',
+      'Starting analysis of samples.',
+      '',
+    ]);
   }, skip: Platform.isWindows);
 }

packages/flutter/lib/src/cupertino/context_menu.dart

@@ -79,10 +79,13 @@ enum _ContextMenuLocation {
 /// This sample shows a very simple CupertinoContextMenu for an empty red
 /// 100x100 Container. Simply long press on it to open.
 ///
+/// ```dart imports
+/// import 'package:flutter/cupertino.dart';
+/// ```
+///
 /// ```dart
 /// Widget build(BuildContext context) {
 ///   return Scaffold(
-///     key: scaffoldKey,
 ///     body: Center(
 ///       child: Container(
 ///         width: 100,