Merge pull request #316 from davidmorgan/better-null-messages

Better null messages

Author: davidmorgan

CHANGELOG.md

@@ -1,7 +1,12 @@
 # Changelog
 
-## 4.5.3
+## 4.6.0
 
+- Add custom `Error` classes: `BuiltValueNullFieldError`,
+  `BuiltValueMissingGenericsError` and `BuiltValueNestedFieldError`. These
+  provide clearer error messages on failure. In particular, errors in nested
+  builders now report the enclosing class and field name, making them much
+  more useful.
 - Fix serialization when using polymorphism with StandardJsonPlugin.
 
 ## 4.5.2

benchmark/lib/node.g.dart

@@ -255,3 +255,46 @@ class FlatBuiltValueToStringHelper implements BuiltValueToStringHelper {
     return stringResult;
   }
 }
+
+/// [Error] indicating that a built_value class constructor was called with
+/// a `null` value for a field not marked `@nullable`.
+class BuiltValueNullFieldError extends Error {
+  final String type;
+  final String field;
+
+  BuiltValueNullFieldError(this.type, this.field);
+
+  @override
+  String toString() =>
+      'Tried to construct class "$type" with null field "$field". '
+      'This is forbidden; to allow it, mark "$field" with @nullable.';
+}
+
+/// [Error] indicating that a built_value class constructor was called with
+/// a missing or `dynamic` type parameter.
+class BuiltValueMissingGenericsError extends Error {
+  final String type;
+  final String parameter;
+
+  BuiltValueMissingGenericsError(this.type, this.parameter);
+
+  @override
+  String toString() =>
+      'Tried to construct class "$type" with missing or dynamic '
+      'type argument "$parameter". All type arguments must be specified.';
+}
+
+/// [Error] indicating that a built_value `build` method failed because a
+/// nested field builder failed.
+class BuiltValueNestedFieldError extends Error {
+  final String type;
+  final String field;
+  final String error;
+
+  BuiltValueNestedFieldError(this.type, this.field, this.error);
+
+  @override
+  String toString() =>
+      'Tried to build class "$type" but nested builder for field "$field" '
+      'threw: $error';
+}