tags warn wwhen using reserved tags (#85631)

changelogs/fragments/tag_u_it.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - tags now warn when using reserved keywords.

changelogs/fragments/warn_reserved_tags.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - ansible now warns if you use reserved tags that were only meant for selection and not for use in play.

lib/ansible/playbook/taggable.py

@@ -19,11 +19,14 @@ from __future__ import annotations
 
 import typing as t
 
+from ansible._internal._templating._engine import TemplateEngine
 from ansible.errors import AnsibleError
 from ansible.module_utils.common.sentinel import Sentinel
 from ansible.module_utils._internal._datatag import AnsibleTagHelper
 from ansible.playbook.attribute import FieldAttribute
-from ansible._internal._templating._engine import TemplateEngine
+from ansible.utils.display import Display
+
+_display = Display()
 
 
 def _flatten_tags(tags: list[str | int]) -> list[str | int]:
@@ -38,17 +41,25 @@ def _flatten_tags(tags: list[str | int]) -> list[str | int]:
 
 class Taggable:
 
+    _RESERVED = frozenset(['tagged', 'all', 'untagged'])
     untagged = frozenset(['untagged'])
     tags = FieldAttribute(isa='list', default=list, listof=(str, int), extend=True)
 
     def _load_tags(self, attr, ds):
+
+        tags = None
         if isinstance(ds, list):
-            return ds
+            tags = ds
+        elif isinstance(ds, str):
+            tags = [AnsibleTagHelper.tag_copy(ds, item.strip()) for item in ds.split(',')]
+
+        if tags is None:
+            raise AnsibleError('tags must be specified as a list', obj=ds)
 
-        if isinstance(ds, str):
-            return [AnsibleTagHelper.tag_copy(ds, item.strip()) for item in ds.split(',')]
+        if found := self._RESERVED.intersection(tags):
+            _display.warning(f"Found reserved tagnames in tags: {list(found)!r}, we do not recommend doing this as it might give unexpected results", obj=ds)
 
-        raise AnsibleError('tags must be specified as a list', obj=ds)
+        return tags
 
     def _get_all_taggable_objects(self) -> t.Iterable[Taggable]:
         obj = self

test/integration/targets/tags/runme.sh

@@ -99,4 +99,8 @@ ansible-playbook test_template_role_tags.yml --tags tag1 "$@" 2>&1 | tee out.txt
 [ "$(grep out.txt -ce 'Tagged_task')" = "1" ]; rm out.txt
 
 ansible-playbook test_template_role_tags.yml --skip-tags tag1 "$@" 2>&1 | tee out.txt
-[ "$(grep out.txt -ce 'Tagged_task')" = "0" ]; rm out.txt
+[ "$(grep out.txt -ce 'Tagged_task')" = "0" ];
+[ "$(grep out.txt -ce 'Found reserved tagsnames')" = "0" ]; rm out.txt
+
+ansible-playbook warn_reserved.yml "$@" 2>&1 | tee out.txt
+[ "$(grep out.txt -ce 'Found reserved tagnames')" = "1" ]; rm out.txt

test/integration/targets/tags/warn_reserved.yml

@@ -0,0 +1,6 @@
+- hosts: all
+  gather_facts: false
+  tasks:
+    - debug: msg=not tagged
+    - debug: msg=taggged
+      tags: tagged