nm: Fix the incorrect change indication for dns option

When applying with `dhcp4: "no"` or `auto6: "no"`, we get incorrect
change indication even when network connection was not changed.

The root cause is the `NM.SettingIPConfig.clear_dns_options(True)` will
create an empty list which will be discard by ifcfg plugin.
The follow up `NM.Connection.compare()` will show configuration changed
as dns option entry missing.

Fixed by remove dns option completely before appending.

Signed-off-by: Gris Ge <fge@redhat.com>

library/network_connections.py

@@ -1044,7 +1044,11 @@ def connection_create(self, connections, idx, connection_current=None):
                     s_ip4.add_dns(nameserver["address"])
             for search_domain in ip["dns_search"]:
                 s_ip4.add_dns_search(search_domain)
-            s_ip4.clear_dns_options(True)
+            # NetworkManager ifcfg plguin will discard empty dns option which
+            # cause follow up NM.Connection.compare() raise false alarm
+            # Use False here to ask NetworkManager remove dns option completely instead
+            # of keeping an empty list
+            s_ip4.clear_dns_options(False)
             for option in ip["dns_options"]:
                 s_ip4.add_dns_option(option)
 
@@ -1086,7 +1090,11 @@ def connection_create(self, connections, idx, connection_current=None):
                     s_ip6.add_dns(nameserver["address"])
             for search_domain in ip["dns_search"]:
                 s_ip6.add_dns_search(search_domain)
-            s_ip6.clear_dns_options(True)
+            # NetworkManager ifcfg plguin will discard empty dns option which
+            # cause follow up NM.Connection.compare() raise false alarm
+            # Use False here to ask NetworkManager remove dns option completely instead
+            # of keeping an empty list
+            s_ip6.clear_dns_options(False)
             for option in ip["dns_options"]:
                 s_ip6.add_dns_option(option)
 

tests/tests_change_indication_on_repeat_run.yml

@@ -33,6 +33,27 @@
                 ip:
                   address:
                     - 192.0.2.2/24
+        - block:
+          - include_role:
+              name: linux-system-roles.network
+            register: __network_connections_result
+          - name: Assert change:true
+            assert:
+              that: __network_connections_result is changed
+          - include_role:
+              name: linux-system-roles.network
+            register: __network_connections_result
+          - name: Assert change:false
+            assert:
+              that: not __network_connections_result is changed
+          vars:
+            network_connections:
+              - name: "{{ interface }}"
+                state: up
+                type: ethernet
+                ip:
+                  dhcp4: "no"
+                  auto6: "no"
       always:
         - block:
             - include_role: