Ensure Try-Dart example sources are analyzed and tested (dart-lang#2124)

* Ensure Try-Dart example sources are analyzed and tested

* Remove dartpad_picker_main dev help files

* Drop demo /try-dart page

* Undo example code changes

Per @mit-mit's request. Will be addressed in a followup PR.

* Drop nullity annotation (in a comment)

examples/misc/bin/try_dart/classes.dart

@@ -0,0 +1,41 @@
+// ignore_for_file: annotate_overrides, sort_constructors_first, type_annotate_public_apis
+// Abstract classes can't be instantiated.
+// ignore: one_member_abstracts
+abstract class Item {
+  use();
+}
+
+// Classes can implement other classes.
+class Chest<T> implements Item {
+  List<T> contents;
+
+  // Constructors can assign arguments to instance variables using `this`.
+  Chest(this.contents);
+
+  use() => print("$this has ${contents.length} items.");
+}
+
+class Sword implements Item {
+  int damage = 5;
+
+  use() => print("$this dealt $damage damage.");
+}
+
+// Classes can extend other classes.
+class DiamondSword extends Sword {
+  int damage = 50; // ignore: overridden_fields
+}
+
+main() {
+  // The 'new' keyword is optional.
+  var chest = Chest<Item>([
+    DiamondSword(),
+    Sword(),
+  ]);
+
+  chest.use();
+
+  for (var item in chest.contents) {
+    item.use();
+  }
+}

examples/misc/bin/try_dart/collection_literals.dart

@@ -0,0 +1,23 @@
+// ignore_for_file: type_annotate_public_apis
+// A list literal.
+var lostNumbers = [4, 8, 15, 16, 23, 42];
+
+// A map literal.
+var nobleGases = {
+  'He': 'Helium',
+  'Ne': 'Neon',
+  'Ar': 'Argon',
+};
+
+// A set literal.
+var frogs = {
+  'Tree',
+  'Poison dart',
+  'Glass',
+};
+
+main() {
+  print(lostNumbers.last);
+  print(nobleGases['Ne']);
+  print(frogs.difference({'Poison dart'}));
+}

examples/misc/bin/try_dart/control_flow.dart

@@ -0,0 +1,26 @@
+bool isEven(int x) {
+  // An if-else statement.
+  if (x % 2 == 0) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+List<int> getEvenNumbers(Iterable<int> numbers) {
+  var evenNumbers = <int>[];
+
+  // A for-in loop.
+  for (var i in numbers) {
+    // A single-line if statement.
+    if (isEven(i)) evenNumbers.add(i);
+  }
+
+  return evenNumbers;
+}
+
+// ignore: type_annotate_public_apis
+main() {
+  var numbers = List.generate(10, (i) => i);
+  print(getEvenNumbers(numbers));
+}

examples/misc/bin/try_dart/functions.dart

@@ -0,0 +1,22 @@
+// A function declaration.
+int timesTwo(int x) {
+  return x * 2;
+}
+
+// Arrow syntax is shorthand for `{ return expr; }`.
+int timesFour(int x) => timesTwo(timesTwo(x));
+
+// Functions are objects.
+int runTwice(int x, Function f) {
+  for (var i = 0; i < 2; i++) {
+    x = f(x); // ignore: invalid_assignment
+  }
+  return x;
+}
+
+// ignore: type_annotate_public_apis
+main() {
+  print("4 times two is ${timesTwo(4)}");
+  print("4 times four is ${timesFour(4)}");
+  print("2 x 2 x 2 is ${runTwice(2, timesTwo)}");
+}

examples/misc/bin/try_dart/strings.dart

@@ -0,0 +1,17 @@
+// ignore: type_annotate_public_apis
+main() {
+  print('a single quoted string');
+  print("a double quoted string");
+
+  // Strings can be combined with the + operator.
+  print("cat" + "dog");
+
+  // Triple quotes define a multi-line string.
+  print('''triple quoted strings
+are for multiple lines''');
+
+  // Dart supports string interpolation.
+  var pi = 3.14;
+  print('pi is $pi');
+  print('tau is ${2 * pi}');
+}

examples/misc/lib/pi_monte_carlo.dart

@@ -10,8 +10,10 @@
 //    e.g., using this Perl regexp: / ?\/\/!.*//g
 
 import 'dart:html'; //!web-only
+// #docregion try-dart
 import 'dart:math' show Random; //!tip("dart:math") //!tip("import")
 
+// #enddocregion try-dart
 int numIterations = 500; //!web-only
 //!web-only
 // We changed a few lines of code to make this sample nicer //!web-only
@@ -20,6 +22,7 @@ int numIterations = 500; //!web-only
 // after 500 iterations). //!web-only
 //!web-only
 //!tip("main()")
+// #docregion try-dart
 main() async {
   print('Compute π using the Monte Carlo method.'); //!tip("π")
   var output = querySelector("#value-of-pi"); //!web-only

examples/misc/pubspec.yaml

@@ -6,7 +6,6 @@ environment:
 
 dev_dependencies:
   args: ^1.5.0
-  test: ^1.0.0
+  examples_util: {path: ../util}
   pedantic: ^1.0.0
-  examples_util:
-    path: ../util
+  test: ^1.0.0

examples/misc/test/try_dart_test.dart

@@ -0,0 +1,36 @@
+import 'package:test/test.dart';
+
+import '../bin/try_dart/functions.dart' as functions;
+import '../bin/try_dart/classes.dart' as classes;
+import '../bin/try_dart/collection_literals.dart' as collection_literals;
+import '../bin/try_dart/control_flow.dart' as control_flow;
+import '../bin/try_dart/strings.dart' as strings;
+
+void main() {
+  test('functions', () {
+    expect(functions.main, prints(endsWith('2 x 2 x 2 is 8\n')));
+  });
+
+  test('control_flow', () {
+    expect(control_flow.main, prints('[0, 2, 4, 6, 8]\n'));
+  });
+
+  test('strings', () {
+    expect(strings.main, prints(endsWith('tau is 6.28\n')));
+  });
+
+  test('collection_literals', () {
+    expect(collection_literals.main, prints('42\nNeon\n{Tree, Glass}\n'));
+  });
+
+  test('classes', () {
+    final output = '''
+      Instance of 'Chest<Item>' has 2 items.
+      Instance of 'DiamondSword' dealt 50 damage.
+      Instance of 'Sword' dealt 5 damage.
+    '''
+        .trimLeft()
+        .replaceAll(RegExp(r'\n\s*'), '\n');
+    expect(classes.main, prints(output));
+  });
+}