Deprecate strategy plugins (#84728)

* Deprecate strategy plugins. Fixes #84725

changelogs/fragments/84725-deprecate-strategy-plugins.yml

@@ -0,0 +1,2 @@
+deprecated_features:
+- Stategy Plugins - Use of strategy plugins not provided in ``ansible.builtin`` are deprecated and do not carry any backwards compatibility guarantees going forward. A future release will remove the ability to use external strategy plugins. No alternative for third party strategy plugins is currently planned.

lib/ansible/plugins/loader.py

@@ -861,7 +861,16 @@ class PluginLoader:
         setattr(obj, 'ansible_name', names[0])
 
     def get(self, name, *args, **kwargs):
-        return self.get_with_context(name, *args, **kwargs).object
+        ctx = self.get_with_context(name, *args, **kwargs)
+        is_core_plugin = ctx.plugin_load_context.plugin_resolved_collection == 'ansible.builtin'
+        if self.class_name == 'StrategyModule' and not is_core_plugin:
+            display.deprecated(  # pylint: disable=ansible-deprecated-no-version
+                'Use of strategy plugins not included in ansible.builtin are deprecated and do not carry '
+                'any backwards compatibility guarantees. No alternative for third party strategy plugins '
+                'is currently planned.'
+            )
+
+        return ctx.object
 
     def get_with_context(self, name, *args, **kwargs):
         """ instantiates a plugin of the given name using arguments """

test/integration/targets/strategy-external/aliases

@@ -0,0 +1,3 @@
+shippable/posix/group5
+context/controller
+needs/target/collection

test/integration/targets/strategy-external/ansible_collections/ns/col/plugins/strategy/external.py

@@ -0,0 +1,7 @@
+from __future__ import annotations
+
+from ansible.plugins.strategy.linear import StrategyModule as LinearStrategy
+
+
+class StrategyModule(LinearStrategy):
+    ...

test/integration/targets/strategy-external/runme.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+source ../collection/setup.sh
+
+set -eux
+export ANSIBLE_DEPRECATION_WARNINGS=1
+export ANSIBLE_COLLECTIONS_PATH="${WORK_DIR}"
+export ANSIBLE_STRATEGY=ns.col.external
+output="$(ansible localhost -m debug 2>&1 | tee -a /dev/stderr)"
+if [[ "${output}" != *"Use of strategy plugins not included in ansible.builtin"* ]]; then
+    echo 'ERROR: Did not find deprecation warning for removal of strategy plugins'
+    exit 1
+fi