feat(parser): support ref-tags with default values

reclass/utils/dictpath.py

@@ -67,6 +67,8 @@ def __init__(self, delim, contents=None):
         elif isinstance(contents, list):
             self._parts = contents
         elif isinstance(contents, six.string_types):
+            # parse the default value from contents, strip default section (||...) from parts            
+            contents, self.default = self._split_default(contents)
             self._parts = self._split_string(contents)
         elif isinstance(contents, tuple):
             self._parts = list(contents)
@@ -115,6 +117,18 @@ def _get_innermost_container(self, base):
     def _split_string(self, string):
         return re.split(r'(?<!\\)' + re.escape(self._delim), string)
 
+    def _split_default(self, string):
+        """
+        splits reference tag 'my:tag||default-value' into two parts
+        """
+        parts = string.split("||")
+        if not parts: 
+            return None # no contents at all
+        elif len(parts) == 1:
+            return parts[0], None # no default
+        else:
+            return parts[:-1][0], parts[-1] # contain '||' in contents and use just the last '||'
+
     def key_parts(self):
         return self._parts[:-1]
 

reclass/values/refitem.py

@@ -29,6 +29,8 @@ def _resolve(self, ref, context):
         try:
             return path.get_value(context)
         except (KeyError, TypeError) as e:
+            if path.default:
+                return path.default
             raise ResolveError(ref)
 
     def render(self, context, inventory):

reclass/values/tests/test_refitem.py

@@ -44,6 +44,11 @@ def test__resolve_ok(self):
 
         self.assertEquals(result, 1)
 
+    def test_default_resolve_ok(self):
+        reference = RefItem('', Settings({'delimiter': ':'}))
+        result = reference._resolve('non:existing||default', {'foo':'bar'})
+        self.assertEquals(result, 'default')
+
     def test__resolve_fails(self):
         refitem = RefItem('', Settings({'delimiter': ':'}))
         context = {'foo':{'bar': 1}}