Prevent infinite recursion when UnpickleableException occurs in a sandbox context. Fixes #440.

CHANGES.txt

@@ -3,6 +3,15 @@ CHANGES
 =======
 
 
+------
+18.8.1
+------
+
+* Issue #440: Prevent infinite recursion when a SandboxViolation
+  or other UnpickleableException occurs in a sandbox context
+  with setuptools hidden. Fixes regression introduced in Setuptools
+  12.0.
+
 ----
 18.8
 ----

setuptools/sandbox.py

@@ -98,8 +98,8 @@ class UnpickleableException(Exception):
     """
     An exception representing another Exception that could not be pickled.
     """
-    @classmethod
-    def dump(cls, type, exc):
+    @staticmethod
+    def dump(type, exc):
         """
         Always return a dumped (pickled) type and exc. If exc can't be pickled,
         wrap it in UnpickleableException first.
@@ -107,6 +107,8 @@ class UnpickleableException(Exception):
         try:
             return pickle.dumps(type), pickle.dumps(exc)
         except Exception:
+            # get UnpickleableException inside the sandbox
+            from setuptools.sandbox import UnpickleableException as cls
             return cls.dump(cls, cls(repr(exc)))