Fix dummy interface returning changed (#3625)

* fix dummy interface bug

* fix dummy interface bug

* Update nmcli.py

* Update nmcli.py

* Update nmcli.py

* Update nmcli.py

* adding tests and requested conditional

* Fix pylint problems and remove 2 lines from previous version of bugfix

* Fix pep8 issue

* add changelog

* Update changelogs/fragments/3625-nmcli_false_changed_mtu_fix.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>

changelogs/fragments/3625-nmcli_false_changed_mtu_fix.yml

@@ -0,0 +1,4 @@
+---
+bugfixes:
+  - nmcli - fixed falsely reported changed status when ``mtu`` is omitted with ``dummy`` connections
+    (https://github.com/ansible-collections/community.general/issues/3612, https://github.com/ansible-collections/community.general/pull/3625).

plugins/modules/net_tools/nmcli.py

@@ -1695,6 +1695,8 @@ class Nmcli(object):
                     # Depending on version nmcli adds double-qoutes to gsm.apn
                     # Need to strip them in order to compare both
                     current_value = current_value.strip('"')
+                if key == self.mtu_setting and self.mtu is None:
+                    self.mtu = 0
             else:
                 # parameter does not exist
                 current_value = None
@@ -1703,6 +1705,8 @@ class Nmcli(object):
                 # compare values between two lists
                 if sorted(current_value) != sorted(value):
                     changed = True
+            elif all([key == self.mtu_setting, self.type == 'dummy', current_value is None, value == 'auto', self.mtu is None]):
+                value = None
             else:
                 if current_value != to_text(value):
                     changed = True

tests/unit/plugins/modules/net_tools/test_nmcli.py

@@ -675,6 +675,45 @@ ipv6.method:                            manual
 ipv6.addresses:                         2001:db8::1/128
 """
 
+TESTCASE_DUMMY_STATIC_WITHOUT_MTU_SHOW_OUTPUT = """\
+connection.id:                          non_existent_nw_device
+connection.interface-name:              dummy_non_existant
+connection.autoconnect:                 yes
+ipv4.method:                            manual
+ipv4.addresses:                         10.10.10.10/24
+ipv4.gateway:                           10.10.10.1
+ipv4.ignore-auto-dns:                   no
+ipv4.ignore-auto-routes:                no
+ipv4.never-default:                     no
+ipv4.may-fail:                          yes
+ipv4.dns:                               1.1.1.1,8.8.8.8
+ipv6.method:                            auto
+ipv6.ignore-auto-dns:                   no
+ipv6.ignore-auto-routes:                no
+ipv6.method:                            manual
+ipv6.addresses:                         2001:db8::1/128
+"""
+
+TESTCASE_DUMMY_STATIC_WITH_CUSTOM_MTU_SHOW_OUTPUT = """\
+connection.id:                          non_existent_nw_device
+connection.interface-name:              dummy_non_existant
+connection.autoconnect:                 yes
+802-3-ethernet.mtu:                     1500
+ipv4.method:                            manual
+ipv4.addresses:                         10.10.10.10/24
+ipv4.gateway:                           10.10.10.1
+ipv4.ignore-auto-dns:                   no
+ipv4.ignore-auto-routes:                no
+ipv4.never-default:                     no
+ipv4.may-fail:                          yes
+ipv4.dns:                               1.1.1.1,8.8.8.8
+ipv6.method:                            auto
+ipv6.ignore-auto-dns:                   no
+ipv6.ignore-auto-routes:                no
+ipv6.method:                            manual
+ipv6.addresses:                         2001:db8::1/128
+"""
+
 
 TESTCASE_GSM = [
     {
@@ -955,6 +994,24 @@ def mocked_dummy_connection_static_unchanged(mocker):
                execute_return=(0, TESTCASE_DUMMY_STATIC_SHOW_OUTPUT, ""))
 
 
+@pytest.fixture
+def mocked_dummy_connection_static_without_mtu_unchanged(mocker):
+    mocker_set(mocker,
+               connection_exists=True,
+               execute_return=(0, TESTCASE_DUMMY_STATIC_WITHOUT_MTU_SHOW_OUTPUT, ""))
+
+
+@pytest.fixture
+def mocked_dummy_connection_static_with_custom_mtu_modify(mocker):
+    mocker_set(mocker,
+               connection_exists=True,
+               execute_return=None,
+               execute_side_effect=(
+                   (0, TESTCASE_DUMMY_STATIC_WITH_CUSTOM_MTU_SHOW_OUTPUT, ""),
+                   (0, "", ""),
+               ))
+
+
 @pytest.fixture
 def mocked_gsm_connection_unchanged(mocker):
     mocker_set(mocker,
@@ -2283,6 +2340,48 @@ def test_dummy_connection_static_unchanged(mocked_dummy_connection_static_unchan
     assert not results['changed']
 
 
+@pytest.mark.parametrize('patch_ansible_module', TESTCASE_DUMMY_STATIC, indirect=['patch_ansible_module'])
+def test_dummy_connection_static_without_mtu_unchanged(mocked_dummy_connection_static_without_mtu_unchanged, capfd):
+    """
+    Test : Dummy connection with static IP configuration and no mtu set unchanged
+    """
+    with pytest.raises(SystemExit):
+        nmcli.main()
+
+    out, err = capfd.readouterr()
+    results = json.loads(out)
+    assert not results.get('failed')
+    assert not results['changed']
+
+
+@pytest.mark.parametrize('patch_ansible_module', TESTCASE_DUMMY_STATIC, indirect=['patch_ansible_module'])
+def test_dummy_connection_static_with_custom_mtu_modify(mocked_dummy_connection_static_with_custom_mtu_modify, capfd):
+    """
+    Test : Dummy connection with static IP configuration and no mtu set modify
+    """
+    with pytest.raises(SystemExit):
+        nmcli.main()
+
+    assert nmcli.Nmcli.execute_command.call_count == 2
+
+    arg_list = nmcli.Nmcli.execute_command.call_args_list
+    args, kwargs = arg_list[1]
+
+    assert args[0][0] == '/usr/bin/nmcli'
+    assert args[0][1] == 'con'
+    assert args[0][2] == 'modify'
+    assert args[0][3] == 'non_existent_nw_device'
+
+    args_text = list(map(to_text, args[0]))
+    for param in ['802-3-ethernet.mtu', '0']:
+        assert param in args_text
+
+    out, err = capfd.readouterr()
+    results = json.loads(out)
+    assert not results.get('failed')
+    assert results['changed']
+
+
 @pytest.mark.parametrize('patch_ansible_module', TESTCASE_GSM, indirect=['patch_ansible_module'])
 def test_create_gsm(mocked_generic_connection_create, capfd):
     """