Don't update job vars too early when getting loop items in TaskExecutor

Fixes #13113

lib/ansible/executor/task_executor.py

@@ -153,16 +153,19 @@ class TaskExecutor:
         and returns the items result.
         '''
 
-        # create a copy of the job vars here so that we can modify
-        # them temporarily without changing them too early for other
-        # parts of the code that might still need a pristine version
-        #vars_copy = self._job_vars.copy()
-        vars_copy = self._job_vars
-
-        # now we update them with the play context vars
-        self._play_context.update_vars(vars_copy)
-
-        templar = Templar(loader=self._loader, shared_loader_obj=self._shared_loader_obj, variables=vars_copy)
+        # save the play context variables to a temporary dictionary,
+        # so that we can modify the job vars without doing a full copy
+        # and later restore them to avoid modifying things too early
+        play_context_vars = dict()
+        self._play_context.update_vars(play_context_vars)
+
+        old_vars = dict()
+        for k in play_context_vars.keys():
+            if k in self._job_vars:
+                old_vars[k] = self._job_vars[k]
+            self._job_vars[k] = play_context_vars[k]
+
+        templar = Templar(loader=self._loader, shared_loader_obj=self._shared_loader_obj, variables=self._job_vars)
         items = None
         if self._task.loop:
             if self._task.loop in self._shared_loader_obj.lookup_loader:
@@ -189,6 +192,15 @@ class TaskExecutor:
             else:
                 raise AnsibleError("Unexpected failure in finding the lookup named '%s' in the available lookup plugins" % self._task.loop)
 
+        # now we restore any old job variables that may have been modified,
+        # and delete them if they were in the play context vars but not in
+        # the old variables dictionary
+        for k in play_context_vars.keys():
+            if k in old_vars:
+                self._job_vars[k] = old_vars[k]
+            else:
+                del self._job_vars[k]
+
         if items:
             from ansible.vars.unsafe_proxy import UnsafeProxy
             for idx, item in enumerate(items):