avoid persistent containers in attribute defaults

lib/ansible/playbook/attribute.py

@@ -32,6 +32,17 @@ def __init__(self, isa=None, private=False, default=None, required=False, listof
         self.priority = priority
         self.always_post_validate = always_post_validate
 
+        # This is here to avoid `default=<container>` unwanted persistence across object instances
+        # We cannot rely on None as some fields use it to skip the code
+        # that would detect an empty container as a user error
+        if self.default == '_ansible_container':
+            if self.isa == 'list':
+                self.default = []
+            elif self.isa == 'dict':
+                self.default = {}
+            elif self.isa == 'set':
+                self.default = set()
+
     def __eq__(self, other):
         return other.priority == self.priority
 

lib/ansible/playbook/block.py

@@ -30,9 +30,9 @@
 
 class Block(Base, Become, Conditional, Taggable):
 
-    _block  = FieldAttribute(isa='list', default=[])
-    _rescue = FieldAttribute(isa='list', default=[])
-    _always = FieldAttribute(isa='list', default=[])
+    _block  = FieldAttribute(isa='list', default='_ansible_container')
+    _rescue = FieldAttribute(isa='list', default='_ansible_container')
+    _always = FieldAttribute(isa='list', default='_ansible_container')
     _delegate_to = FieldAttribute(isa='list')
     _delegate_facts = FieldAttribute(isa='bool', default=False)
 

lib/ansible/playbook/conditional.py

@@ -33,7 +33,7 @@ class Conditional:
     to be run conditionally when a condition is met or skipped.
     '''
 
-    _when = FieldAttribute(isa='list', default=[])
+    _when = FieldAttribute(isa='list', default='_ansible_container')
 
     def __init__(self, loader=None):
         # when used directly, this class needs a loader, but we want to

lib/ansible/playbook/play.py

@@ -64,22 +64,22 @@ class Play(Base, Taggable, Become):
 
     # Connection
     _gather_facts        = FieldAttribute(isa='bool', default=None, always_post_validate=True)
-    _hosts               = FieldAttribute(isa='list', default=[], required=True, listof=string_types, always_post_validate=True)
+    _hosts               = FieldAttribute(isa='list', default='_ansible_container', required=True, listof=string_types, always_post_validate=True)
     _name                = FieldAttribute(isa='string', default='', always_post_validate=True)
 
     # Variable Attributes
-    _vars_files          = FieldAttribute(isa='list', default=[], priority=99)
-    _vars_prompt         = FieldAttribute(isa='list', default=[], always_post_validate=True)
+    _vars_files          = FieldAttribute(isa='list', default='_ansible_container', priority=99)
+    _vars_prompt         = FieldAttribute(isa='list', default='_ansible_container', always_post_validate=True)
     _vault_password      = FieldAttribute(isa='string', always_post_validate=True)
 
     # Role Attributes
-    _roles               = FieldAttribute(isa='list', default=[], priority=90)
+    _roles               = FieldAttribute(isa='list', default='_ansible_container', priority=90)
 
     # Block (Task) Lists Attributes
-    _handlers            = FieldAttribute(isa='list', default=[])
-    _pre_tasks           = FieldAttribute(isa='list', default=[])
-    _post_tasks          = FieldAttribute(isa='list', default=[])
-    _tasks               = FieldAttribute(isa='list', default=[])
+    _handlers            = FieldAttribute(isa='list', default='_ansible_container')
+    _pre_tasks           = FieldAttribute(isa='list', default='_ansible_container')
+    _post_tasks          = FieldAttribute(isa='list', default='_ansible_container')
+    _tasks               = FieldAttribute(isa='list', default='_ansible_container')
 
     # Flag/Setting Attributes
     _any_errors_fatal    = FieldAttribute(isa='bool', default=False, always_post_validate=True)

lib/ansible/playbook/play_context.py

@@ -171,8 +171,8 @@ class PlayContext(Base):
 
     # general flags
     _verbosity        = FieldAttribute(isa='int', default=0)
-    _only_tags        = FieldAttribute(isa='set', default=set())
-    _skip_tags        = FieldAttribute(isa='set', default=set())
+    _only_tags        = FieldAttribute(isa='set', default='_ansible_container')
+    _skip_tags        = FieldAttribute(isa='set', default='_ansible_container')
     _check_mode       = FieldAttribute(isa='bool', default=False)
     _force_handlers   = FieldAttribute(isa='bool', default=False)
     _start_at_task    = FieldAttribute(isa='string')

lib/ansible/playbook/playbook_include.py

@@ -35,7 +35,7 @@ class PlaybookInclude(Base, Conditional, Taggable):
 
     _name      = FieldAttribute(isa='string')
     _include   = FieldAttribute(isa='string')
-    _vars      = FieldAttribute(isa='dict', default=dict())
+    _vars      = FieldAttribute(isa='dict', default='_ansible_container')
 
     @staticmethod
     def load(data, basedir, variable_manager=None, loader=None):

lib/ansible/playbook/role/metadata.py

@@ -40,7 +40,7 @@ class RoleMetadata(Base):
     '''
 
     _allow_duplicates = FieldAttribute(isa='bool', default=False)
-    _dependencies     = FieldAttribute(isa='list', default=[])
+    _dependencies     = FieldAttribute(isa='list', default='_ansible_container')
     _galaxy_info      = FieldAttribute(isa='GalaxyInfo')
 
     def __init__(self, owner=None):

lib/ansible/playbook/taggable.py

@@ -29,7 +29,7 @@
 class Taggable:
 
     untagged = frozenset(['untagged'])
-    _tags = FieldAttribute(isa='list', default=[], listof=(string_types,int))
+    _tags = FieldAttribute(isa='list', default='_ansible_container', listof=(string_types,int))
 
     def __init__(self):
         super(Taggable, self).__init__()

lib/ansible/playbook/task.py

@@ -64,7 +64,7 @@ class Task(Base, Conditional, Taggable, Become):
     # will be used if defined
     # might be possible to define others
 
-    _args                 = FieldAttribute(isa='dict', default=dict())
+    _args                 = FieldAttribute(isa='dict', default='_ansible_container')
     _action               = FieldAttribute(isa='string')
 
     _any_errors_fatal     = FieldAttribute(isa='bool')