Added custom error types for construction errors.

Author: davidmorgan

benchmark/lib/simple_value.g.dart

@@ -255,3 +255,31 @@ 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.';
+}

built_value/lib/built_value.dart

@@ -356,7 +356,7 @@ abstract class ValueSourceClass
       result.writeln('{');
       for (final field in requiredFields) {
         result.writeln("if (${field.name} == null) "
-            "throw new ArgumentError.notNull('${field.name}');");
+            "throw new BuiltValueNullFieldError('${name}', '${field.name}');");
       }
       result.writeln('}');
     }
@@ -523,10 +523,9 @@ abstract class ValueSourceClass
     } else {
       result.writeln('{');
       for (final genericParameter in genericParameters) {
-        result.writeln(
-            'if ($genericParameter == dynamic) throw new ArgumentError.value('
-            "'dynamic', '$genericParameter', "
-            "'All type arguments must be specified');");
+        result.writeln('if ($genericParameter == dynamic) '
+            'throw new BuiltValueMissingGenericsError('
+            "'$name', '$genericParameter');");
       }
       result.writeln('}');
     }