Added ability to limit role dependencies to just one inclusion

docsite/latest/rst/playbooks.rst

@@ -568,10 +568,10 @@ Role dependencies can also be specified as a full path, just like top level role
     dependencies:
        - { role: '/path/to/common/roles/foo', x: 1 }
 
-Roles dependencies are always executed before the role that includes them, and are recursive.
-
-Role dependencies may be included more than once. Continuing the above example, the 'car' role could 
-add 'wheel' dependencies as follows::
+Roles dependencies are always executed before the role that includes them, and are recursive. By default, 
+roles can also only be added as a dependency once - if another role also lists it as a dependency it will
+not be run again. This behavior can be overridden by adding `allow_duplicates: yes` to the `meta/main.yml` file.
+For example, a role named 'car' could add a role named 'wheel' to its dependencies as follows::
 
     ---
     dependencies:
@@ -580,7 +580,15 @@ add 'wheel' dependencies as follows::
     - { role: wheel, n: 3 }
     - { role: wheel, n: 4 }
 
-If the wheel role required tire and brake in turn, this would result in the following execution order::
+And the `meta/main.yml` for wheel contained the following::
+
+    ---
+    allow_duplicates: yes
+    dependencies:
+    - { role: tire }
+    - { role: brake }
+
+The resulting order of execution would be as follows::
 
     tire(n=1)
     brake(n=1)

lib/ansible/playbook/play.py

@@ -29,7 +29,7 @@ class Play(object):
 
     __slots__ = [
        'hosts', 'name', 'vars', 'default_vars', 'vars_prompt', 'vars_files',
-       'handlers', 'remote_user', 'remote_port',
+       'handlers', 'remote_user', 'remote_port', 'included_roles',
        'sudo', 'sudo_user', 'transport', 'playbook',
        'tags', 'gather_facts', 'serial', '_ds', '_handlers', '_tasks',
        'basedir', 'any_errors_fatal', 'roles', 'max_fail_pct'
@@ -75,6 +75,7 @@ class Play(object):
         self._update_vars_files_for_host(None)
 
         # now we load the roles into the datastructure
+        self.included_roles = []
         ds = self._load_roles(self.roles, ds)
         
         # and finally re-process the vars files as they may have
@@ -177,6 +178,16 @@ class Play(object):
                     dependencies = data.get('dependencies',[])
                     for dep in dependencies:
                         (dep_path,dep_vars) = self._get_role_path(dep)
+                        meta = self._resolve_main(utils.path_dwim(self.basedir, os.path.join(dep_path, 'meta')))
+                        if os.path.isfile(meta):
+                            meta_data = utils.parse_yaml_from_file(meta)
+                            if meta_data:
+                                allow_dupes = utils.boolean(meta_data.get('allow_duplicates',''))
+                                if not allow_dupes:
+                                    if dep.get('role') in self.included_roles:
+                                        continue
+                                    else:
+                                        self.included_roles.append(dep.get('role'))
                         dep_vars = utils.combine_vars(passed_vars, dep_vars)
                         dep_vars = utils.combine_vars(role_vars, dep_vars)
                         vars = self._resolve_main(utils.path_dwim(self.basedir, os.path.join(dep_path, 'vars')))