add custom module type validation (#27183)

* Module argument_spec now accepts a callable for the type argument, which is passed through and called with the value when appropriate. On validation/conversion failure, the name of the callable (or its type as a fallback) is used in the error message.
* adds basic smoke tests for custom callable validator functionality

test/units/module_utils/basic/test_argument_spec.py

@@ -0,0 +1,49 @@
+# Copyright (c) 2017 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)
+__metaclass__ = type
+
+import json
+
+from ansible.compat.tests import unittest
+from ansible.compat.tests.mock import MagicMock
+from units.mock.procenv import swap_stdin_and_argv, swap_stdout
+from ansible.module_utils import basic
+
+
+class TestCallableTypeValidation(unittest.TestCase):
+    def setUp(self):
+        args = json.dumps(dict(ANSIBLE_MODULE_ARGS=dict(arg="42")))
+        self.stdin_swap_ctx = swap_stdin_and_argv(stdin_data=args)
+        self.stdin_swap_ctx.__enter__()
+
+        # since we can't use context managers and "with" without overriding run(), call them directly
+        self.stdout_swap_ctx = swap_stdout()
+        self.fake_stream = self.stdout_swap_ctx.__enter__()
+
+        basic._ANSIBLE_ARGS = None
+
+    def tearDown(self):
+        # since we can't use context managers and "with" without overriding run(), call them directly to clean up
+        self.stdin_swap_ctx.__exit__(None, None, None)
+        self.stdout_swap_ctx.__exit__(None, None, None)
+
+    def test_validate_success(self):
+        mock_validator = MagicMock(return_value=42)
+        m = basic.AnsibleModule(argument_spec=dict(
+            arg=dict(type=mock_validator)
+        ))
+
+        self.assertTrue(mock_validator.called)
+        self.assertEqual(m.params['arg'], 42)
+        self.assertEqual(type(m.params['arg']), int)
+
+    def test_validate_fail(self):
+        mock_validator = MagicMock(side_effect=TypeError("bad conversion"))
+        with self.assertRaises(SystemExit) as ecm:
+            m = basic.AnsibleModule(argument_spec=dict(
+                arg=dict(type=mock_validator)
+            ))
+
+        self.assertIn("bad conversion", json.loads(self.fake_stream.getvalue())['msg'])