update sample code analyzer regexp & test case (#30201)

updates the regex the analyzer uses, so it should be able to recognize expressions such as
const Foo a = Foo(); as "other code" rather than a constructor call.

dev/bots/analyze-sample-code.dart

@@ -165,7 +165,7 @@ class SampleChecker {
   static final RegExp _codeBlockEndRegex = RegExp(r'///\s+```\s*$');
 
   /// A RegExp that matches a Dart constructor.
-  static final RegExp _constructorRegExp = RegExp(r'[A-Z][a-zA-Z0-9<>.]*\(');
+  static final RegExp _constructorRegExp = RegExp(r'(const\s+)?_*[A-Z][a-zA-Z0-9<>._]*\(');
 
   /// Whether or not to keep the temp directory around after running.
   ///
@@ -742,7 +742,7 @@ linter:
     if (block.isEmpty) {
       throw SampleCheckerException('$line: Empty ```dart block in sample code.');
     }
-    if (block.first.startsWith('new ') || block.first.startsWith('const ') || block.first.startsWith(_constructorRegExp)) {
+    if (block.first.startsWith('new ') || block.first.startsWith(_constructorRegExp)) {
       _expressionId += 1;
       return Section.surround(line, 'dynamic expression$_expressionId = ', block.toList(), ';');
     } else if (block.first.startsWith('await ')) {

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

@@ -7,6 +7,10 @@
 
 // Examples can assume:
 // bool _visible = true;
+// class _Text extends Text {
+//   const _Text(String text) : super(text);
+//   const _Text.__(String text) : super(text);
+// }
 
 /// A blabla that blabla its blabla blabla blabla.
 ///
@@ -41,3 +45,41 @@
 /// )
 /// ```
 /// {@end-tool}
+///
+/// {@tool sample}
+/// regular const constructor
+///
+/// ```dart
+/// const Text('Poor wandering ones!')
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// const private constructor
+/// ```dart
+/// const             _Text('Poor wandering ones!')
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// yet another const private constructor
+/// ```dart
+/// const        _Text.__('Poor wandering ones!')
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// const variable
+///
+/// ```dart
+/// const text0 = Text('Poor wandering ones!');
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// more const variables
+///
+/// ```dart
+/// const text1 = _Text('Poor wandering ones!');
+/// ```
+/// {@end-tool}

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

@@ -17,14 +17,14 @@ void main() {
       ..removeWhere((String line) => line.startsWith('Analyzer output:'));
     expect(process.exitCode, isNot(equals(0)));
     expect(stderrLines, <String>[
-      'known_broken_documentation.dart:26:9: new Opacity(',
+      'known_broken_documentation.dart:30:9: new Opacity(',
       '>>> Unnecessary new keyword (unnecessary_new)',
-      'known_broken_documentation.dart:38:9: new Opacity(',
+      'known_broken_documentation.dart:42:9: new Opacity(',
       '>>> Unnecessary new keyword (unnecessary_new)',
       '',
       'Found 1 sample code errors.',
       '',
     ]);
-    expect(stdoutLines, <String>['Found 2 sample code sections.', 'Starting analysis of samples.', '']);
+    expect(stdoutLines, <String>['Found 7 sample code sections.', 'Starting analysis of samples.', '']);
   }, skip: Platform.isWindows);
 }