Load role vars and defaults before parsing tasks (#40982)

* Load role vars and defaults before parsing tasks. Fixes #40163

* Add porting guide note

* Wording clarifications

* typo

* grammar fixes

docs/docsite/rst/porting_guides/porting_guide_2.7.rst

@@ -17,7 +17,14 @@ This document is part of a collection on porting. The complete list of porting g
 Playbook
 ========
 
-No notable changes.
+Role Precedence Fix during Role Loading
+---------------------------------------
+
+Ansible 2.7 makes a small change to variable precedence when loading roles, resolving a bug, ensuring that role loading matches :ref:`variable precedence expectations <ansible_variable_precedence>`.
+
+Before Ansible 2.7, when loading a role, the variables defined in the role's ``vars/main.yml`` and ``defaults/main.yml`` were not available when parsing the role's ``tasks/main.yml`` file. This prevented the role from utilizing these variables when being parsed. The problem manifested when ``import_tasks`` or ``import_role`` was used with a variable defined in the role's vars or defaults.
+
+In Ansible 2.7, role ``vars`` and ``defaults`` are now parsed before ``tasks/main.yml``. This can cause a change in behavior if the same variable is defined at the play level and the role level with different values, and leveraged in ``import_tasks`` or ``import_role`` to define the role or file to import.
 
 Deprecated
 ==========

lib/ansible/playbook/role/__init__.py

@@ -197,6 +197,19 @@ class Role(Base, Become, Conditional, Taggable):
                 if os.path.isdir(plugin_path):
                     obj.add_directory(plugin_path)
 
+        # vars and default vars are regular dictionaries
+        self._role_vars = self._load_role_yaml('vars', main=self._from_files.get('vars'), allow_dir=True)
+        if self._role_vars is None:
+            self._role_vars = dict()
+        elif not isinstance(self._role_vars, dict):
+            raise AnsibleParserError("The vars/main.yml file for role '%s' must contain a dictionary of variables" % self._role_name)
+
+        self._default_vars = self._load_role_yaml('defaults', main=self._from_files.get('defaults'), allow_dir=True)
+        if self._default_vars is None:
+            self._default_vars = dict()
+        elif not isinstance(self._default_vars, dict):
+            raise AnsibleParserError("The defaults/main.yml file for role '%s' must contain a dictionary of variables" % self._role_name)
+
         # load the role's other files, if they exist
         metadata = self._load_role_yaml('meta')
         if metadata:
@@ -222,19 +235,6 @@ class Role(Base, Become, Conditional, Taggable):
                 raise AnsibleParserError("The handlers/main.yml file for role '%s' must contain a list of tasks" % self._role_name,
                                          obj=handler_data, orig_exc=e)
 
-        # vars and default vars are regular dictionaries
-        self._role_vars = self._load_role_yaml('vars', main=self._from_files.get('vars'), allow_dir=True)
-        if self._role_vars is None:
-            self._role_vars = dict()
-        elif not isinstance(self._role_vars, dict):
-            raise AnsibleParserError("The vars/main.yml file for role '%s' must contain a dictionary of variables" % self._role_name)
-
-        self._default_vars = self._load_role_yaml('defaults', main=self._from_files.get('defaults'), allow_dir=True)
-        if self._default_vars is None:
-            self._default_vars = dict()
-        elif not isinstance(self._default_vars, dict):
-            raise AnsibleParserError("The defaults/main.yml file for role '%s' must contain a dictionary of variables" % self._role_name)
-
     def _load_role_yaml(self, subdir, main=None, allow_dir=False):
         file_path = os.path.join(self._role_path, subdir)
         if self._loader.path_exists(file_path) and self._loader.is_directory(file_path):