Add a custom Boolean type in order to be able to provide custom descriptive message along the error code

rest_condition/mixins.py

@@ -0,0 +1,35 @@
+__all__ = ('UpdatedPermissionChecksMixin',)
+
+class UpdatedPermissionChecksMixin(object):
+    """
+    Updated permission checks mixin.
+    """
+    def check_permissions(self, request):
+        """
+        Check if the request should be permitted.
+        Raises an appropriate exception if the request is not permitted.
+        """
+        for permission in self.get_permissions():
+            has_perm = permission.has_permission(request, self)
+            if not has_perm:
+                message = has_perm.message \
+                    if hasattr(has_perm, 'message') and has_perm.message \
+                    else getattr(permission, 'message', None)
+                self.permission_denied(
+                    request, message=message
+                )
+
+    def check_object_permissions(self, request, obj):
+        """
+        Check if the request should be permitted for a given object.
+        Raises an appropriate exception if the request is not permitted.
+        """
+        for permission in self.get_permissions():
+            has_perm = permission.has_object_permission(request, self, obj)
+            if not has_perm:
+                message = has_perm.message \
+                    if hasattr(has_perm, 'message') and has_perm.message \
+                    else getattr(permission, 'message', None)
+                self.permission_denied(
+                    request, message=message
+                )

rest_condition/permissions.py

@@ -5,6 +5,9 @@
 import operator
 from rest_framework import permissions
 
+# Import from rest_framework.types once the pull request is merged
+from .types import Boolean
+
 __all__ = ['ConditionalPermission', 'Condition', 'C', 'And', 'Or', 'Not']
 
 _NONE = object()
@@ -82,6 +85,7 @@ def __init__(self, *perms_or_conds, **kwargs):
 
     def evaluate_permissions(self, permission_name, *args, **kwargs):
         reduced_result = _NONE
+        messages = []
 
         for condition in self.perms_or_conds:
             if hasattr(condition, 'evaluate_permissions'):
@@ -91,6 +95,13 @@ def evaluate_permissions(self, permission_name, *args, **kwargs):
                     condition = condition()
                 result = getattr(condition, permission_name)(*args, **kwargs)
 
+            message = result.message \
+                if hasattr(result, 'message') and result.message \
+                else None
+
+            if message:
+                messages.append(message)
+
             if reduced_result is _NONE:
                 reduced_result = result
             else:
@@ -100,9 +111,10 @@ def evaluate_permissions(self, permission_name, *args, **kwargs):
                 break
 
         if reduced_result is not _NONE:
-            return not reduced_result if self.negated else reduced_result
+            ret = not reduced_result if self.negated else reduced_result
+            return Boolean(ret, '; '.join(messages))
 
-        return False
+        return Boolean(False, '; '.join(messages))
 
     def has_object_permission(self, request, view, obj):
         return self.evaluate_permissions('has_object_permission',

rest_condition/types.py

@@ -0,0 +1,7 @@
+__all__ = ('Boolean',)
+
+class Boolean(int):
+    def __new__(cls, x, message):
+        obj = int.__new__(cls, x)
+        obj.message = message
+        return obj