pkg/docgen: support better const rendering of String, List, and empty Map

pkg/docgen/lib/src/model_helpers.dart

Index: pkg/docgen/lib/src/model_helpers.dart
diff --git a/pkg/docgen/lib/src/model_helpers.dart b/pkg/docgen/lib/src/model_helpers.dart
index 678fa19394cd84fbddc2dfeff3954eadee302452..1820b1d97770346d340df4e9ea5ac62b98b1f5eb 100644
--- a/pkg/docgen/lib/src/model_helpers.dart
+++ b/pkg/docgen/lib/src/model_helpers.dart
@@ -17,6 +17,41 @@ import 'library_helpers.dart' show includePrivateMembers;
 import 'models.dart';
 import 'package_helpers.dart';
 
+String getDefaultValue(ParameterMirror mirror) {
+  if (!mirror.hasDefaultValue) return null;
+  return getDefaultValueFromConstMirror(mirror.defaultValue);
+}
+
+String getDefaultValueFromConstMirror(
+    dart2js_mirrors.Dart2JsConstantMirror valueMirror) {
+
+  if (valueMirror is dart2js_mirrors.Dart2JsStringConstantMirror) {
+    return '"${valueMirror.reflectee}"';
+  }
+
+  if (valueMirror is dart2js_mirrors.Dart2JsListConstantMirror) {
+    var buffer = new StringBuffer('[');
+
+    var values = new Iterable.generate(valueMirror.length,
+        (i) => valueMirror.getElement(i))
+        .map((e) => getDefaultValueFromConstMirror(e));
+
+    buffer.writeAll(values, ', ');
+
+    buffer.write(']');
+    return buffer.toString();
+  }
+
+  if (valueMirror is dart2js_mirrors.Dart2JsMapConstantMirror) {
+    // TODO(kevmoo) Handle non-empty case
+    if (valueMirror.length == 0) return '{}';
+  }
+
+  // TODO(kevmoo) Handle consts of non-core types
+
+  return '${valueMirror}';
+}
+
 /// Returns a list of meta annotations assocated with a mirror.
 List<Annotation> createAnnotations(DeclarationMirror mirror,
     Library owningLibrary) {