PluginLoader now installs module-to-be-imported in sys.modules before exec (as Python import does). (#78364)

changelogs/fragments/self_referential.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - Fix PluginLoader to mimic Python import machinery by adding module to sys.modules before exec

lib/ansible/plugins/loader.py

@@ -796,11 +796,22 @@ class PluginLoader:
             return sys.modules[full_name]
 
         with warnings.catch_warnings():
+            # FIXME: this still has issues if the module was previously imported but not "cached",
+            #  we should bypass this entire codepath for things that are directly importable
             warnings.simplefilter("ignore", RuntimeWarning)
             spec = importlib.util.spec_from_file_location(to_native(full_name), to_native(path))
             module = importlib.util.module_from_spec(spec)
-            spec.loader.exec_module(module)
+
+            # mimic import machinery; make the module-being-loaded available in sys.modules during import
+            # and remove if there's a failure...
             sys.modules[full_name] = module
+
+            try:
+                spec.loader.exec_module(module)
+            except Exception:
+                del sys.modules[full_name]
+                raise
+
         return module
 
     def _update_object(self, obj, name, path, redirected_names=None):

test/integration/targets/plugin_loader/normal/action_plugins/self_referential.py

@@ -0,0 +1,29 @@
+# Copyright: Contributors to the Ansible project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.plugins.action import ActionBase
+
+import sys
+
+# reference our own module from sys.modules while it's being loaded to ensure the importer behaves properly
+try:
+    mod = sys.modules[__name__]
+except KeyError:
+    raise Exception(f'module {__name__} is not accessible via sys.modules, likely a pluginloader bug')
+
+
+class ActionModule(ActionBase):
+    TRANSFERS_FILES = False
+
+    def run(self, tmp=None, task_vars=None):
+        if task_vars is None:
+            task_vars = dict()
+
+        result = super(ActionModule, self).run(tmp, task_vars)
+        del tmp  # tmp no longer has any effect
+
+        result['changed'] = False
+        result['msg'] = 'self-referential action loaded and ran successfully'
+        return result

test/integration/targets/plugin_loader/normal/self_referential.yml

@@ -0,0 +1,5 @@
+- hosts: testhost
+  gather_facts: false
+  tasks:
+    - name: ensure a self-referential action plugin loads properly
+      self_referential: