avocado.core.tree: Support for using

Support for '!using' flag. It extends the current leaf location
of the provided path. It can't completely change the location,
it only extends the base.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/tree.py

@@ -47,6 +47,7 @@ except ImportError:
 
 # Mapping for yaml flags
 YAML_INCLUDE = 0
+YAML_USING = 1
 
 
 class TreeNode(object):
@@ -324,17 +325,31 @@ def _create_from_yaml(path, cls_node=TreeNode):
     def tree_node_from_values(name, values):
         """ Create `name` node and add values  """
         node = cls_node(str(name))
+        using = ''
         for value in values:
             if isinstance(value, TreeNode):
                 node.add_child(value)
             elif isinstance(value[0], Control):
-                # Include file
-                ypath = value[1]
-                if not os.path.isabs(ypath):
-                    ypath = os.path.join(os.path.dirname(path), ypath)
-                node.merge(_create_from_yaml(ypath, cls_node))
+                if value[0] == YAML_INCLUDE:
+                    # Include file
+                    ypath = value[1]
+                    if not os.path.isabs(ypath):
+                        ypath = os.path.join(os.path.dirname(path), ypath)
+                    node.merge(_create_from_yaml(ypath, cls_node))
+                elif value[0] == YAML_USING:
+                    if using:
+                        raise ValueError("!using can be used only once per "
+                                         "node! (%s:%s)" % (path, name))
+                    using = value[1]
+                    if using[0] == '/':
+                        using = using[1:]
+                    if using[-1] == '/':
+                        using = using[:-1]
             else:
                 node.value[value[0]] = value[1]
+        if using:
+            for name in using.split('/')[::-1]:
+                node = cls_node(name, children=[node])
         return node
 
     def mapping_to_tree_loader(loader, node):
@@ -360,6 +375,8 @@ def _create_from_yaml(path, cls_node=TreeNode):
 
     Loader.add_constructor(u'!include',
                            lambda loader, node: Control(YAML_INCLUDE))
+    Loader.add_constructor(u'!using',
+                           lambda loader, node: Control(YAML_USING))
     Loader.add_constructor(yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
                            mapping_to_tree_loader)
 

docs/source/MultiplexConfig.rst

@@ -66,6 +66,51 @@ The ending nodes (the leafs on the tree) will become part of all lower-level
 However, the precedence is evaluated in top-down or ``last defined`` order.
 In other words, the last parsed has precedence over earlier definitions.
 
+Additionally you can prepend multiple nodes to the given node by using
+`!using : $prepended/path`. This is useful when extending complex structure,
+for example imagine having distro variants in separate ymal files. In the
+end you want to merge them into the `/os` node. The main file can be simply::
+
+    # main.yaml
+    os:
+        !include : os/fedora/21.yaml
+        ....
+
+And each file can look either like this::
+
+    # fedora/21.yaml
+    fedora:
+        21:
+            some: value
+
+or you can use `!using` which prepends the `fedora/21`::
+
+    # fedora/21.yaml
+    !using : /fedora/21
+    some: value
+
+To be precise there is a way to define the structure in the main yaml file::
+
+    # main.yaml
+    os:
+        fedora:
+            21:
+                !include : fedora_21.yaml
+
+Or use recursive `!include` (slower)::
+
+    # main.yaml
+    os:
+        fedora:
+            !include : os/fedora.yaml
+    # os/fedora.yaml
+    21:
+        !include : fedora/21.yaml
+    # os/fedora/21.yaml
+    some: value
+
+Due to yaml nature, it's __mandatory__ to put space between `!using` and `:`!
+
 .. _keys_and_values:
 
 Keys and Values

examples/mux-selftest-advanced.yaml

+# Put everything into /virt
+!using : /virt
 # Following line makes it look exactly as mux-selftest.yaml
 !include : mux-selftest.yaml
 distro:
@@ -5,4 +7,8 @@ distro:
     !include : mux-selftest-distro.yaml
 # This creates new branch the usual way
 new_node:
+    # Put this new_node into /absolutely/fresh/ ('/' are automatically
+    # removed during parse time, absolute location is not supported and
+    # not even planned)
+    !using : /absolutely/fresh/
     new_value: "something"

selftests/all/unit/avocado/tree_unittest.py

@@ -157,12 +157,14 @@ class TestTree(unittest.TestCase):
         exp = ['intel', 'amd', 'arm', 'scsi', 'virtio', 'fedora', 'mint', '6',
                '7', 'prod', 'new_node']
         act = tree2.get_leaves()
+        oldroot = tree2.children[0]
         self.assertEqual(exp, act)
         self.assertEqual({'enterprise': True},
-                         tree2.children[1].children[2].value)
+                         oldroot.children[1].children[2].value)
         self.assertEqual({'init': 'systemd'},
-                         tree2.children[1].children[0].value)
-        self.assertEqual({'new_value': 'something'}, tree2.children[3].value)
+                         oldroot.children[1].children[0].value)
+        self.assertEqual({'new_value': 'something'},
+                         oldroot.children[3].children[0].children[0].value)
 
 
 class TestPathParent(unittest.TestCase):