avocado.core.tree: Support for remove_value

This patch adds support for '!remove_value' yaml tag. It can be used
to remove certain value from previously existing values. This happens
during merge before value is updated.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/tree.py

@@ -50,6 +50,7 @@ except ImportError:
 YAML_INCLUDE = 0
 YAML_USING = 1
 YAML_REMOVE_NODE = 2
+YAML_REMOVE_VALUE = 3
 
 
 class Control(object):  # Few methods pylint: disable=R0903
@@ -129,7 +130,6 @@ class TreeNode(object):
         added as children (recursively they get either appended at the end
         or merged into existing node in the previous position.
         """
-        self.value.update(other.value)
         for ctrl in other.ctrl:
             if isinstance(ctrl, Control):
                 if ctrl.code == YAML_REMOVE_NODE:
@@ -140,6 +140,15 @@ class TreeNode(object):
                             remove.append(child)
                     for child in remove:
                         self.children.remove(child)
+                elif ctrl.code == YAML_REMOVE_VALUE:
+                    remove = []
+                    regexp = re.compile(ctrl.value)
+                    for key in self.value.iterkeys():
+                        if regexp.match(key):
+                            remove.append(key)
+                    for key in remove:
+                        self.value.pop(key, None)
+        self.value.update(other.value)
         for child in other.children:
             self.add_child(child)
 
@@ -350,6 +359,9 @@ def _create_from_yaml(path, cls_node=TreeNode):
                 elif value[0].code == YAML_REMOVE_NODE:
                     value[0].value = value[1]   # set the name
                     node.ctrl.append(value[0])    # add "blue pill" of death
+                elif value[0].code == YAML_REMOVE_VALUE:
+                    value[0].value = value[1]   # set the name
+                    node.ctrl.append(value[0])
             else:
                 node.value[value[0]] = value[1]
         if using:
@@ -384,6 +396,8 @@ def _create_from_yaml(path, cls_node=TreeNode):
                            lambda loader, node: Control(YAML_USING))
     Loader.add_constructor(u'!remove_node',
                            lambda loader, node: Control(YAML_REMOVE_NODE))
+    Loader.add_constructor(u'!remove_value',
+                           lambda loader, node: Control(YAML_REMOVE_VALUE))
     Loader.add_constructor(yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
                            mapping_to_tree_loader)
 

docs/source/MultiplexConfig.rst

@@ -163,6 +163,22 @@ And lists::
 
 The list above will become ``['-O2', '-g', '-Wall']`` to Python. In fact,
 YAML is compatible to JSON.
+
+It's also possible to remove key using python's regexp, which can be useful
+when extending upstream file using downstream yaml files. This is done by
+`!remove_value : $value_name` directive::
+
+    debug:
+        CFLAGS: '-O0 -g'
+    debug:
+        !remove_value: CFLAGS
+
+removes the CFLAGS value completely from the debug node. This happens during
+the merge and only once. So if you switch the two, CFLAGS would be defined.
+
+Due to yaml nature, it's __mandatory__ to put space between `!remove_value`
+and `:`!
+
 .. _environment:
 
 Environment

examples/mux-selftest-advanced.yaml

@@ -10,6 +10,15 @@ distro:
     # This is a new /distro/mint appended as latest child
     mint:
         new_mint: True
+    fedora:
+        !remove_value : init.*
+        new_init: systemd
+    gentoo:
+        # This modifies the value of 'is_cool'
+        is_cool: True
+        # And this removes the original 'is_cool'
+        # Setting happens after ctrl so it should be created'
+        !remove_value : is_cool
 # This creates new branch the usual way
 new_node:
     # Put this new_node into /absolutely/fresh/ ('/' are automatically

examples/mux-selftest-distro.yaml

@@ -4,3 +4,5 @@ RHEL:
         init: 'systemv'
     7:
         init: 'systemd'
+gentoo:
+    is_cool: False

selftests/all/unit/avocado/tree_unittest.py

@@ -153,14 +153,16 @@ class TestTree(unittest.TestCase):
     def test_advanced_yaml(self):
         tree2 = tree.create_from_yaml(['examples/mux-selftest-advanced.yaml'])
         exp = ['intel', 'amd', 'arm', 'scsi', 'virtio', 'fedora', '6',
-               '7', 'mint', 'prod', 'new_node']
+               '7', 'gentoo', 'mint', 'prod', 'new_node']
         act = tree2.get_leaves()
         oldroot = tree2.children[0]
         self.assertEqual(exp, act)
         self.assertEqual({'enterprise': True},
                          oldroot.children[1].children[1].value)
-        self.assertEqual({'init': 'systemd'},
+        self.assertEqual({'new_init': 'systemd'},
                          oldroot.children[1].children[0].value)
+        self.assertEqual({'is_cool': True},
+                         oldroot.children[1].children[2].value)
         self.assertEqual({'new_value': 'something'},
                          oldroot.children[3].children[0].children[0].value)