add context to RestValidationError

Author: Lukáš Klíma

docs/exceptions.rst

@@ -122,4 +122,4 @@ Pyston forms exception classes are defined in ``pyston.forms``.
 .. exception:: RestValidationError
 
     ``RestValidationError`` is similar to Django ``ValidationError`` but it can contain only one error message with one
-    code.
+    code and context.

pyston/forms/__init__.py

@@ -136,13 +136,15 @@ def __str__(self):
 
 class RestValidationError(RestError):
 
-    def __init__(self, message, code=None):
+    def __init__(self, message, code=None, context=None):
         if isinstance(message, (RestValidationError, ValidationError)):
             self.message = message.message
             self.code = message.code
+            self.context = getattr(message, 'context', {}) | (context or {})
         else:
             self.message = message
             self.code = code or DEFAULT_CODE
+            self.context = context or {}
 
     def __str__(self):
         return self.message
@@ -613,7 +615,9 @@ def _parse_rest_errors(self, errors):
         elif isinstance(errors, dict):
             return RestDictError({k: self._parse_rest_errors(v) for k, v in errors.items()})
         else:
-            return RestValidationError(list(errors.as_data()[0])[0], errors.as_data()[0].code)
+            error = errors.as_data()[0]
+            context = error.params if isinstance(error, ValidationError) else None
+            return RestValidationError(list(error)[0], error.code, context=context)
 
     def is_invalid(self):
         """