Add auto-fixing implementation for no-handler rule

.github/workflows/tox.yml

@@ -71,7 +71,7 @@ jobs:
       WSLENV: FORCE_COLOR:PYTEST_REQPASS:TOXENV:GITHUB_STEP_SUMMARY
       # Number of expected test passes, safety measure for accidental skip of
       # tests. Update value if you add/remove tests.
-      PYTEST_REQPASS: 822
+      PYTEST_REQPASS: 823
     steps:
       - name: Activate WSL1
         if: "contains(matrix.shell, 'wsl')"

examples/playbooks/transform-no-handler.transformed.yml

@@ -0,0 +1,16 @@
+---
+- name: Example of no-handler rule
+  hosts: localhost
+  tasks:
+    - name: Register result of a task
+      ansible.builtin.copy:
+        dest: /tmp/placeholder
+        content: Ansible made this!
+        mode: "0600"
+      register: result # <-- we register the result of the task
+
+  handlers:
+    - name: Second command to run
+      ansible.builtin.debug:
+        msg: The placeholder file was modified!
+      when: result.changed # <-- this triggers no-handler rule

examples/playbooks/transform-no-handler.yml

@@ -0,0 +1,15 @@
+---
+- name: Example of no-handler rule
+  hosts: localhost
+  tasks:
+    - name: Register result of a task
+      ansible.builtin.copy:
+        dest: /tmp/placeholder
+        content: Ansible made this!
+        mode: "0600"
+      register: result # <-- we register the result of the task
+
+    - name: Second command to run
+      ansible.builtin.debug:
+        msg: The placeholder file was modified!
+      when: result.changed # <-- this triggers no-handler rule

src/ansiblelint/rules/no_handler.py

@@ -24,11 +24,14 @@
 import sys
 from typing import TYPE_CHECKING
 
-from ansiblelint.rules import AnsibleLintRule
+from ruamel.yaml.comments import CommentedMap, CommentedSeq
+
+from ansiblelint.rules import AnsibleLintRule, TransformMixin
+from ansiblelint.utils import Task
 
 if TYPE_CHECKING:
+    from ansiblelint.errors import MatchError
     from ansiblelint.file_utils import Lintable
-    from ansiblelint.utils import Task
 
 
 def _changed_in_when(item: str) -> bool:
@@ -50,7 +53,7 @@ def _changed_in_when(item: str) -> bool:
     )
 
 
-class UseHandlerRatherThanWhenChangedRule(AnsibleLintRule):
+class UseHandlerRatherThanWhenChangedRule(AnsibleLintRule, TransformMixin):
     """Tasks that run when changed should likely be handlers."""
 
     id = "no-handler"
@@ -82,6 +85,31 @@ def matchtask(
             result = _changed_in_when(when)
         return result
 
+    def transform(
+        self,
+        match: MatchError,
+        lintable: Lintable,
+        data: CommentedMap | CommentedSeq | str,
+    ) -> None:
+        if match.tag == self.id and isinstance(data, CommentedSeq):
+            is_fixed = False
+            task_name = None
+            if isinstance(match.task, Task):
+                task_name = match.task.get("name")
+
+            for item in data:
+                # Item is a play
+                # Look for handlers at the play level
+                if "handlers" not in item:
+                    item["handlers"] = CommentedSeq()
+                for k, v in enumerate(item.get("tasks")):
+                    if v["name"] == task_name:
+                        item["handlers"].append(item.get("tasks").pop(k))
+                        is_fixed = True
+
+            if is_fixed:
+                match.fixed = True
+
 
 if "pytest" in sys.modules:
     import pytest

test/test_transformer.py

@@ -116,6 +116,12 @@ def fixture_runner_result(
             True,
             id="partial_become",
         ),
+        pytest.param(
+            "examples/playbooks/transform-no-handler.yml",
+            1,
+            True,
+            id="transform_no_handler",
+        ),
     ),
 )
 def test_transformer(  # pylint: disable=too-many-arguments, too-many-locals