Make CheckedFromJsonException ctor public

Fixes #187

Author: kevmoo

json_annotation/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.2.6
 
+* `CheckedFromJsonException`
+  * The constructor is now public.
+  * The `message` property is now `String` (instead of `Object`).
+
 * Added `JsonKey.defaultValue`.
 
 * Added helpers for deserialization of `enum` values.

json_annotation/lib/src/checked_helpers.dart

@@ -23,7 +23,7 @@ T $checkedNew<T>(String className, Map map, T constructor(),
     if (error is ArgumentError) {
       key = fieldKeyMap[error.name] ?? error.name;
     }
-    throw new CheckedFromJsonException._(error, stack, map, key,
+    throw new CheckedFromJsonException(error, stack, map, key,
         className: className);
   }
 }
@@ -38,28 +38,44 @@ T $checkedConvert<T>(Map map, String key, T castFunc(Object value)) {
   } on CheckedFromJsonException {
     rethrow;
   } catch (error, stack) {
-    throw new CheckedFromJsonException._(error, stack, map, key);
+    throw new CheckedFromJsonException(error, stack, map, key);
   }
 }
 
 /// Exception thrown if there is a runtime exception in `fromJson`
 /// code generated when `JsonSerializableGenerator.checked` is `true`
 class CheckedFromJsonException implements Exception {
+  /// The [Error] or [Exception] that triggered this exception.
   final Object innerError;
+
+  /// The [StackTrace] for the [Error] or [Exception] that triggered this
+  /// exception.
   final StackTrace innerStack;
+
+  /// The key from [map] that corresponds to the thrown [innerError].
+  ///
+  /// May be `null`.
   final String key;
+
+  /// The source [Map] that was used for decoding when the [innerError] was
+  /// thrown.
   final Map map;
-  final Object message;
 
-  String _className;
+  /// A human-readable message corresponding to [innerError].
+  ///
+  /// May be `null`.
+  final String message;
+
+  /// The name of the class being created when [innerError] was thrown.
   String get className => _className;
+  String _className;
 
-  CheckedFromJsonException._(
-      this.innerError, this.innerStack, this.map, this.key,
+  /// Creates a new instance of [CheckedFromJsonException].
+  CheckedFromJsonException(this.innerError, this.innerStack, this.map, this.key,
       {String className})
       : _className = className,
         message = _getMessage(innerError);
 
-  static Object _getMessage(Object error) =>
-      (error is ArgumentError) ? error.message : null;
+  static String _getMessage(Object error) =>
+      (error is ArgumentError) ? error.message?.toString() : null;
 }