dart:convert: support indented output w/ JsonEncoder

tests/lib/convert/json_pretty_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library json_pretty_test;
+
+import 'dart:convert';
+
+import 'package:matcher/matcher.dart';
+
+void main() {
+  // indent less than zero is coerced to zero
+  var encoder = const JsonEncoder.withIndent(-2);
+  expect(encoder.indent, 0);
+
+  _expect(null, 'null');
+
+  _expect([1, 2, 3, 4], '''
+[
+  1,
+  2,
+  3,
+  4
+]''');
+
+  _expect([true, null, 'hello', 42.42],
+      '''
+[
+  true,
+  null,
+  "hello",
+  42.42
+]''');
+
+  _expect({"hello": [], "goodbye": {} } ,
+'''{
+  "hello": [],
+  "goodbye": {}
+}''');
+
+  _expect(["test", 1, 2, 33234.324, true, false, null, {
+      "test1": "test2",
+      "test3": "test4",
+      "grace": 5,
+      "shanna": [0, 1, 2]
+    }, {
+      "lib": "app.dart",
+      "src": ["foo.dart", "bar.dart"]
+    }],
+        '''[
+  "test",
+  1,
+  2,
+  33234.324,
+  true,
+  false,
+  null,
+  {
+    "test1": "test2",
+    "test3": "test4",
+    "grace": 5,
+    "shanna": [
+      0,
+      1,
+      2
+    ]
+  },
+  {
+    "lib": "app.dart",
+    "src": [
+      "foo.dart",
+      "bar.dart"
+    ]
+  }
+]''');
+}
+
+void _expect(Object object, String expected) {
+  var encoder = const JsonEncoder.withIndent(2);
+  var prettyOutput = encoder.convert(object);
+
+  expect(prettyOutput, expected);
+
+  encoder = const JsonEncoder.withIndent(0);
+
+  var flatOutput = encoder.convert(object);
+
+  var flatExpected = const LineSplitter().convert(expected)
+      .map((line) => line.trimLeft())
+      .join('\n');
+
+  expect(flatOutput, flatExpected);
+
+  var compactOutput = JSON.encode(object);
+
+  encoder = const JsonEncoder.withIndent(null);
+  expect(encoder.convert(object), compactOutput);
+
+  var prettyDecoded = JSON.decode(prettyOutput);
+
+  expect(JSON.encode(prettyDecoded), compactOutput);
+}