[FIX] namespace packages: move from pkg_resources-style to pkg_util

Deprecates the previous pkg_resources-style packages. Our use was
not entirely spec compliant, and it broke with setuptools 31.
More information in odoo#15718

Instead, use the pkgutil-style namespace packages.
This is spec compliant as long as all other distributions providing
odoo.addons use PEP 420 namespace packages (i.e. no __init__.py).
So this mechanism fully works on Python 3 only, but does not break
anything on Python 2.

See also:
https://packaging.python.org/guides/packaging-namespace-packages/#pkgutil-style-namespace-packages

Closes odoo#19517
Fixes odoo#15718

odoo-bin

@@ -2,7 +2,6 @@
 
 # set server timezone in UTC before time module imported
 __import__('os').environ['TZ'] = 'UTC'
-__import__('pkg_resources').declare_namespace('odoo.addons')
 import odoo
 
 if __name__ == "__main__":

odoo/__init__.py

@@ -3,6 +3,12 @@
 
 """ OpenERP core library."""
 
+#----------------------------------------------------------
+# odoo must be a namespace package for odoo.addons to become one too
+# https://packaging.python.org/guides/packaging-namespace-packages/
+#----------------------------------------------------------
+__path__ = __import__('pkgutil').extend_path(__path__, __name__)
+
 #----------------------------------------------------------
 # Running mode flags (gevent, prefork)
 #----------------------------------------------------------

odoo/addons/__init__.py

@@ -14,4 +14,7 @@
 Importing them from here is deprecated.
 
 """
-__import__('pkg_resources').declare_namespace(__name__)
+# make odoo.addons a namespace package, while keeping this __init__.py
+# present, for python 2 compatibility
+# https://packaging.python.org/guides/packaging-namespace-packages/
+__path__ = __import__('pkgutil').extend_path(__path__, __name__)

setup/odoo

@@ -2,7 +2,6 @@
 
 # set server timezone in UTC before time module imported
 __import__('os').environ['TZ'] = 'UTC'
-__import__('pkg_resources').declare_namespace('odoo.addons')
 import odoo
 
 if __name__ == "__main__":