checkPythonSourceCode: add a cache

When using checkPythonSourceCode integrated in the source code editor,
for a scenario where developer edit a component and save we can benefit
from caching the check message for the source code content, because the
same check that the one happening in the editor will happen when the
component is saved.

This cache varies on:
 - "component_packages" cache cookie which is reset every time some
component code is edited.
 - zope startup time to take into account editions of file system code.
This assumes that after reseting file system code zope will be
restarted.
 - portal_type, because the checks performed by this function also
depend on portal type.

product/ERP5Type/Utils.py

@@ -427,14 +427,35 @@ def fill_args_from_request(*optional_args):
 _pylint_message_re = re.compile(
   '^(?P<type>[CRWEF]):\s*(?P<row>\d+),\s*(?P<column>\d+):\s*(?P<message>.*)$')
 
+zope_startup_time = time.time()
 def checkPythonSourceCode(source_code_str, portal_type=None):
   """
   Check source code with pylint or compile() builtin if not available.
 
+  `portal_type` argument can be passed to the checker, to adapt the checks
+  based on the portal type.
+
+  This function is cached, so checkin the same code several times is instant.
+
   TODO-arnau: Get rid of NamedTemporaryFile (require a patch on pylint to
               allow passing a string) and this should probably return a proper
               ERP5 object rather than a dict...
   """
+  # late imports because we have a circular import dependency here.
+  from Products.ERP5Type.Cache import CachingMethod
+  from Products.ERP5.ERP5Site import getSite
+  checkPythonSourceCode = CachingMethod(
+      _checkPythonSourceCode,
+      '_checkPythonSourceCode.{}.{}.{}'.format(
+          zope_startup_time,
+          md5_new(source_code_str).hexdigest(),
+          getSite().getCacheCookie('component_packages')))
+  # normalize type of portal_type argument to maximize cache hits.
+  if isinstance(portal_type, unicode):
+    portal_type = portal_type.encode()
+  return checkPythonSourceCode(source_code_str, portal_type)
+
+def _checkPythonSourceCode(source_code_str, portal_type):
   if not source_code_str:
     return []