Split the JSON output into multiple lines.

pkg/dart_messages/lib/shared_messages.dart

 // Copyright (c) 2015, 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.
 
 // An update to this file must be followed by regenerating the corresponding
 // json, dart2js and analyzer file. Use `publish.dart` in the bin directory.
 //
 // Every message in this file must have an id. Use `message_id.dart` in the
 // bin directory to generate a fresh one.
 
@@ skipping 120 matching lines @@
       this.category,
       this.template,
       this.templateHoleOrder,
       this.howToFix,
       this.options,
       this.usedBy: const [],
       this.examples});
 }
 
 String get messagesAsJson {
-  var jsonified = {};
+  var jsonifiedEntries = [];
   MESSAGES.forEach((String name, Message message) {
-    jsonified[name] = {
+    jsonifiedEntries.add("'$name': " + JSON.encode({

[Siggi Cherem (dart-lang), 2016/02/18 20:55:02]

or use `const JsonEncoder.withIndent('  ').encode(jsonified)`?

[floitsch, 2016/02/18 21:00:48]

Even better.
Dart really has great libraries ;)

       'id': message.id,
       'subId': message.subId,
       'category': message.category.name,
       'template': message.template,
       'templateHoleOrder': message.templateHoleOrder,
       'howToFix': message.howToFix,
       'options': message.options,
       'usedBy': message.usedBy.map((platform) => platform.toString()).toList(),
       'examples': message.examples,
-    };
+    }));
   });
-  return JSON.encode(jsonified);
+  return """
+  {
+    ${jsonifiedEntries.join(",\n")}
+  }""";
 }
 
 final Map<String, Message> MESSAGES = {
   'exampleMessage': new Message(
       id: 'use an Id generated by bin/message_id.dart',
       category: Category.analysisOptionsError,
       template: "#use #named #arguments",
       templateHoleOrder: ["arguments", "named", "use"],
       howToFix: "an explanation on how to fix things",
       examples: [
@@ skipping 311 matching lines @@
         """
         foo() async* { return 0; }
         main() => foo();
         """,
         """
         foo() sync* { return 0; }
         main() => foo();
         """
       ]),
 };