Support for module param defaults (#22648)

test/integration/targets/module_defaults/tasks/main.yml

@@ -0,0 +1,89 @@
+- name: main block
+  vars:
+    test_file: /tmp/ansible-test.module_defaults.foo
+  module_defaults:
+    debug:
+      msg: test default
+    file:
+      path: '{{ test_file }}'
+  block:
+    - debug:
+      register: foo
+
+    - name: test that 'debug' task used default 'msg' param
+      assert:
+        that: foo.msg == "test default"
+
+    - name: remove test file
+      file:
+        state: absent
+
+    - name: touch test file
+      file:
+        state: touch
+
+    - name: stat test file
+      stat:
+        path: '{{ test_file }}'
+      register: foo
+
+    - name: check that test file exists
+      assert:
+        that: foo.stat.exists
+
+    - name: remove test file
+      file:
+        state: absent
+
+    - name: test that module defaults from parent are inherited and merged
+      module_defaults:
+        # Meaningless values to make sure that 'module_defaults' gets
+        # evaluated for this block
+        foo:
+          bar: baz
+      block:
+      - debug:
+        register: foo
+
+      - assert:
+          that: foo.msg == "test default"
+
+    - name: test that we can override module defaults inherited from parent
+      module_defaults:
+        debug:
+          msg: "different test message"
+      block:
+      - debug:
+        register: foo
+
+      - assert:
+          that: foo.msg == "different test message"
+
+    - name: test that module defaults inherited from parent can be removed
+      module_defaults:
+        debug: {}
+      block:
+      - debug:
+        register: foo
+
+      - assert:
+          that:
+            foo.msg == "Hello world!"
+
+    - name: test that module defaults can be overridden by module params
+      block:
+      - debug:
+          msg: another test message
+        register: foo
+
+      - assert:
+          that:
+            foo.msg == "another test message"
+
+      - debug:
+          msg: '{{ omit }}'
+        register: foo
+
+      - assert:
+          that:
+            foo.msg == "Hello world!"