[FIX] fields: when computing digits, use an existing cursor instead of a new one

The computation of property `digits` was creating a new cursor to call the
function that determines digits.  This technique is fragile because the current
cursor may have pending updates that the new cursor will not see.

The issue was discovered by Cécile Tonglet (cto).  She observed an infinite
loop during a database migration, and a traceback inside the loop showed the
presence of the `digits` property.  This change fixes the infinite loop issue.

openerp/api.py

@@ -68,7 +68,7 @@ from pprint import pformat
 from weakref import WeakSet
 from werkzeug.local import Local, release_local
 
-from openerp.tools import frozendict
+from openerp.tools import frozendict, classproperty
 
 _logger = logging.getLogger(__name__)
 
@@ -674,6 +674,10 @@ class Environment(object):
     """
     _local = Local()
 
+    @classproperty
+    def envs(cls):
+        return cls._local.environments
+
     @classmethod
     @contextmanager
     def manage(cls):
@@ -699,7 +703,7 @@ class Environment(object):
         args = (cr, uid, context)
 
         # if env already exists, return it
-        env, envs = None, cls._local.environments
+        env, envs = None, cls.envs
         for env in envs:
             if env.args == args:
                 return env

openerp/fields.py

@@ -1054,8 +1054,10 @@ class Float(Field):
     @property
     def digits(self):
         if callable(self._digits):
-            with registry().cursor() as cr:
-                return self._digits(cr)
+            # retrieve a cursor from any environment
+            from openerp.api import Environment
+            cr = next(iter(Environment.envs)).cr
+            return self._digits(cr)
         else:
             return self._digits
 

openerp/osv/fields.py

@@ -388,8 +388,10 @@ class float(_column):
     @property
     def digits(self):
         if self._digits_compute:
-            with registry().cursor() as cr:
-                return self._digits_compute(cr)
+            # retrieve a cursor from any environment
+            from openerp.api import Environment
+            cr = next(iter(Environment.envs)).cr
+            return self._digits_compute(cr)
         else:
             return self._digits
 
@@ -1309,8 +1311,10 @@ class function(_column):
     @property
     def digits(self):
         if self._digits_compute:
-            with registry().cursor() as cr:
-                return self._digits_compute(cr)
+            # retrieve a cursor from any environment
+            from openerp.api import Environment
+            cr = next(iter(Environment.envs)).cr
+            return self._digits_compute(cr)
         else:
             return self._digits