[FIX] safe_eval: no shadowing of PostgreSQL's exceptions

Letting PostgreSQL low-level exceptions bubble up
ensures that the mechanism for automatically
retrying transactions will work.
In case of transient errors such as deadlocks or
serialization errors, the transaction will be
transparently retried. Previously they were
transformed into ValueError and caused a permanent
failure immediately.

The fallback to ValueError is meant for invalid
expressions or expressions that use variables not
provided in the evaluation context. Other
exception types should be preserved (this is
further improved in Odoo 8)

openerp/tools/safe_eval.py

@@ -32,6 +32,7 @@ condition/math builtins.
 #  - safe_eval in tryton http://hg.tryton.org/hgwebdir.cgi/trytond/rev/bbb5f73319ad
 
 from opcode import HAVE_ARGUMENT, opmap, opname
+from psycopg2 import OperationalError
 from types import CodeType
 import logging
 
@@ -285,6 +286,10 @@ def safe_eval(expr, globals_dict=None, locals_dict=None, mode="eval", nocopy=Fal
     )
     try:
         return eval(test_expr(expr, _SAFE_OPCODES, mode=mode), globals_dict, locals_dict)
+    except OperationalError:
+        # Do not hide PostgreSQL low-level exceptions, to let the auto-replay
+        # of serialized transactions work its magic
+        raise
     except Exception:
         _logger.exception('Cannot eval %r', expr)
         raise