grains state: allow deleting grain with 'False' value

and destroy a grain previously set to None, with destructive=True:

The f46722aaeb commit, from Bruno Binet <bruno.binet@gmail.com> was
effectively reverted during my work on nested and complex values support.

This commit get it back, plus the ability to destroy a existing grain that
was previously set to None, plus tests for these.

salt/modules/grains.py

@@ -628,7 +628,8 @@ def set(key,
     elif isinstance(_existing_value, list):
         _existing_value_type = 'complex'
 
-    if _existing_value_type is not None and _existing_value == val:
+    if _existing_value_type is not None and _existing_value == val \
+                   and (val is not None or destructive is not True):
         ret['comment'] = 'Grain is already set'
         return ret
 

salt/states/grains.py

@@ -264,13 +264,33 @@ def absent(name,
         grains.absent
     '''
 
+    _non_existent_key = 'NonExistentValueMagicNumberSpK3hnufdHfeBUXCfqVK'
+
     name = re.sub(delimiter, DEFAULT_TARGET_DELIM, name)
     ret = {'name': name,
            'changes': {},
            'result': True,
            'comment': ''}
-    grain = __salt__['grains.get'](name, None)
-    if grain:
+    grain = __salt__['grains.get'](name, _non_existent_key)
+    if grain is None:
+        if __opts__['test']:
+            ret['result'] = None
+            if destructive is True:
+                ret['comment'] = 'Grain {0} is set to be deleted'\
+                    .format(name)
+                ret['changes'] = {'deleted': name}
+            return ret
+        ret = __salt__['grains.set'](name,
+                                     None,
+                                     destructive=destructive,
+                                     force=force)
+        if ret['result']:
+            if destructive is True:
+                ret['comment'] = 'Grain {0} was deleted'\
+                    .format(name)
+                ret['changes'] = {'deleted': name}
+        ret['name'] = name
+    elif grain != _non_existent_key:
         if __opts__['test']:
             ret['result'] = None
             if destructive is True:

tests/unit/states/grains_test.py

@@ -549,6 +549,20 @@ class GrainsTestCase(TestCase):
                                   + "foo: null\n"
         )
 
+        # Unset grain when its value is False
+        self.setGrains({'a': 'aval', 'foo': False})
+        ret = grains.absent(
+            name='foo')
+        self.assertEqual(ret['result'], True)
+        self.assertEqual(ret['comment'], 'Value for grain foo was set to None')
+        self.assertEqual(ret['changes'], {'grain': 'foo', 'value': None})
+        self.assertEqual(
+            grains.__grains__,
+            {'a': 'aval', 'foo': None})
+        self.assertGrainFileContent("a: aval\n"
+                                  + "foo: null\n"
+        )
+
         # Unset a nested grain
         self.setGrains({'a': 'aval', 'foo': ['order', {'is': {'nested': 'bar'}}, 'correct']})
         ret = grains.absent(
@@ -651,6 +665,19 @@ class GrainsTestCase(TestCase):
             {'a': 'aval'})
         self.assertGrainFileContent("a: aval\n")
 
+        # Delete a previously unset grain
+        self.setGrains({'a': 'aval', 'foo': None})
+        ret = grains.absent(
+            name='foo',
+            destructive=True)
+        self.assertEqual(ret['result'], True)
+        self.assertEqual(ret['comment'], 'Grain foo was deleted')
+        self.assertEqual(ret['changes'], {'deleted': 'foo'})
+        self.assertEqual(
+            grains.__grains__,
+            {'a': 'aval'})
+        self.assertGrainFileContent("a: aval\n")
+
         # Delete a nested grain
         self.setGrains({'a': 'aval', 'foo': ['order', {'is': {'nested': 'bar', 'other': 'value'}}, 'correct']})
         ret = grains.absent(