Add a check for file with only comments

That should catch things like __init__.py files with only license
headers inside.

Change-Id: I6a2078f6264ef252d4eb431c8df33db0913ba3bf

doc/source/index.rst

@@ -285,6 +285,8 @@ All source files should have the following header:
     #    License for the specific language governing permissions and limitations
     #    under the License.
 
+Files with no code shouldn't contain any license header nor comments, and
+must be left completely empty.
 
 Commit Messages
 ---------------

hacking/__init__.py

@@ -1,14 +0,0 @@
-# Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#    http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
-# implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.

hacking/core.py

@@ -228,6 +228,19 @@ def hacking_has_correct_license(physical_line, filename, lines, line_number):
                     "License notice")
 
 
+EMPTY_LINE_RE = re.compile("^\s*(#.*|$)")
+
+
+@flake8ext
+def hacking_has_only_comments(physical_line, filename, lines, line_number):
+    """Check for empty files with only comments
+
+    H104 empty file with only comments
+    """
+    if line_number == 1 and all(map(EMPTY_LINE_RE.match, lines)):
+        return (0, "H104: File contains nothing but comments")
+
+
 @flake8ext
 def hacking_except_format(logical_line, physical_line):
     r"""Check for 'except:'.

hacking/tests/test_core.py

@@ -0,0 +1,62 @@
+# Copyright (c) 2013 eNovance
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from hacking import core
+from hacking import tests
+
+
+class CoreTestCase(tests.TestCase):
+    def test_H104_regex(self):
+        """Verify that the H104 regex matches correct lines."""
+        self.assertTrue(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo',
+             '# bar'],
+            1))
+        self.assertTrue(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo',
+             '# bar',
+             ''],
+            1))
+        self.assertTrue(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo',
+             '   ',
+             '# bar'],
+            1))
+
+        self.assertIsNone(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo',
+             '   ',
+             '"""foobar"""'],
+            1))
+        self.assertIsNone(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo',
+             '',
+             'print(42)'],
+            1))
+        self.assertIsNone(core.hacking_has_only_comments(
+            None,
+            None,
+            ['# foo'],
+            100))

hacking/tests/test_doctest.py

@@ -66,7 +66,10 @@ def _get_lines(check):
 
 def load_tests(loader, tests, pattern):
 
-    flake8_style = engine.get_style_guide(parse_argv=False, ignore='F')
+    flake8_style = engine.get_style_guide(parse_argv=False,
+                                          # Ignore H104 otherwise it's
+                                          # raised on doctests.
+                                          ignore=('F', 'H104'))
     options = flake8_style.options
 
     for name, check in hacking.core.__dict__.items():

setup.cfg

@@ -26,6 +26,7 @@ flake8.extension =
     H101 = hacking.core:hacking_todo_format
     H102 = hacking.core:hacking_has_license
     H103 = hacking.core:hacking_has_correct_license
+    H104 = hacking.core:hacking_has_only_comments
     H201 = hacking.core:hacking_except_format
     H202 = hacking.core:hacking_except_format_assert
     H231 = hacking.core:hacking_python3x_except_compatible