Prevent new code from using namespaced oslo imports

Ib63da2d845843410634a1df0261af33b973daf32 is an example where
new code had to be fixed for oslo_concurrency imports. Let us
add a hacking check to prevent such regression. When we update
to new oslo libraries with non-namespace'd imports, we should
update the regexp in this hacking rule

Change-Id: I44536d477d06ddc1205b824bcb888b666405dce3

HACKING.rst

@@ -45,6 +45,7 @@ Nova Specific Commandments
 - [N330] Validate that LOG.warning messages use _LW.
 - [N331] Change LOG.warn on LOG.warning.
 - [N332] Check that the api_version decorator is the first decorator on a method
+- [N333] Check for oslo library imports use the non-namespaced packages
 
 Creating Unit Tests
 -------------------

nova/hacking/checks.py

@@ -75,6 +75,10 @@ underscore_import_check = re.compile(r"(.)*import _(.)*")
 custom_underscore_check = re.compile(r"(.)*_\s*=\s*(.)*")
 api_version_re = re.compile(r"@.*api_version")
 
+# TODO(dims): When other oslo libraries switch over non-namespace'd
+# imports, we need to add them to the regexp below.
+oslo_namespace_imports = re.compile(r"from[\s]*oslo[.](concurrency)")
+
 
 class BaseASTChecker(ast.NodeVisitor):
     """Provides a simple framework for writing AST-based checks.
@@ -445,6 +449,14 @@ class CheckForTransAdd(BaseASTChecker):
         super(CheckForTransAdd, self).generic_visit(node)
 
 
+def check_oslo_namespace_imports(logical_line, blank_before, filename):
+    if re.match(oslo_namespace_imports, logical_line):
+        msg = ("N333: '%s' must be used instead of '%s'.") % (
+               logical_line.replace('oslo.', 'oslo_'),
+               logical_line)
+        yield(0, msg)
+
+
 def factory(register):
     register(import_no_db_in_virt)
     register(no_db_session_in_public_api)
@@ -466,3 +478,4 @@ def factory(register):
     register(check_api_version_decorator)
     register(CheckForStrUnicodeExc)
     register(CheckForTransAdd)
+    register(check_oslo_namespace_imports)

nova/tests/unit/test_hacking.py

@@ -367,6 +367,13 @@ class HackingTestCase(test.NoDBTestCase):
         self._assert_has_errors(code, checks.check_api_version_decorator,
                                 expected_errors=[(2, 0, "N332")])
 
+    def test_oslo_namespace_imports_check(self):
+        code = """
+               from oslo.concurrency import processutils
+               """
+        self._assert_has_errors(code, checks.check_oslo_namespace_imports,
+                                expected_errors=[(1, 0, "N333")])
+
     def test_trans_add(self):
 
         checker = checks.CheckForTransAdd