Description of problem:

The following desired state, which contains undefined property under ipv4 subtree can be successfully applied:

interfaces:
- name: eth1
  type: ethernet
  state: up
  ipv4:
    doesntexist: blah
    enabled: false
    address:
    - ip: 192.168.0.1
      prefix-length: 24


Only when enabled is set to true, the configuration fails on an error similar to the following paste:

Traceback (most recent call last):
  File "/usr/bin/nmstatectl", line 11, in <module>
    load_entry_point('nmstate==1.1.0', 'console_scripts', 'nmstatectl')()
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 74, in main
    return args.func(args)
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 338, in set
    return apply(args)
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 355, in apply
    args.save_to_disk,
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 419, in apply_state
    save_to_disk=save_to_disk,
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 90, in apply
    _apply_ifaces_state(plugins, net_state, verify_change, save_to_disk)
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 141, in _apply_ifaces_state
    _verify_change(plugins, net_state)
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 156, in _verify_change
    net_state.verify(current_state)
  File "/usr/lib/python3.6/site-packages/libnmstate/net_state.py", line 86, in verify
    self._ifaces.verify(current_state.get(Interface.KEY))
  File "/usr/lib/python3.6/site-packages/libnmstate/ifaces/ifaces.py", line 665, in verify
    cur_iface.state_for_verify(),
libnmstate.error.NmstateVerificationError: 
desired
=======
---
name: eth1
type: ethernet
state: up
ipv4:
  enabled: true
  address:
  - ip: 192.168.0.1
    prefix-length: 24
  doesntexist: absent

current
=======
---
name: eth1
type: ethernet
state: up
accept-all-mac-addresses: false
ethernet:
  auto-negotiation: false
ethtool:
  feature:
    rx-gro: true
    rx-gro-list: false
    rx-udp-gro-forwarding: false
    tx-checksum-ip-generic: true
    tx-generic-segmentation: true
    tx-nocache-copy: false
    tx-tcp-ecn-segmentation: true
    tx-tcp-mangleid-segmentation: false
    tx-tcp-segmentation: true
    tx-tcp6-segmentation: true
  ring:
    rx: 256
    tx: 256
ipv4:
  enabled: true
  address:
  - ip: 192.168.0.1
    prefix-length: 24
  dhcp: false
ipv6:
  enabled: false
lldp:
  enabled: false
mac-address: 52:55:00:D1:56:02
mtu: 1500

difference
==========
--- desired
+++ current
@@ -2,9 +2,33 @@
 name: eth1
 type: ethernet
 state: up
+accept-all-mac-addresses: false
+ethernet:
+  auto-negotiation: false
+ethtool:
+  feature:
+    rx-gro: true
+    rx-gro-list: false
+    rx-udp-gro-forwarding: false
+    tx-checksum-ip-generic: true
+    tx-generic-segmentation: true
+    tx-nocache-copy: false
+    tx-tcp-ecn-segmentation: true
+    tx-tcp-mangleid-segmentation: false
+    tx-tcp-segmentation: true
+    tx-tcp6-segmentation: true
+  ring:
+    rx: 256
+    tx: 256
 ipv4:
   enabled: true
   address:
   - ip: 192.168.0.1
     prefix-length: 24
-  doesntexist: absent
+  dhcp: false
+ipv6:
+  enabled: false
+lldp:
+  enabled: false
+mac-address: 52:55:00:D1:56:02
+mtu: 1500



According to the documentation, ipv4.enabled is false, all other properties are ignored. But it seems it would be better 
to perform verification to make sure the ipv4 properties are sane.
It's easy to imagine that a user would have a desired state with disabled and enabled ipv4 stack and the unexistent property.
When enabling the ipv4, the configuration would fail on a seemingly unrelated error.

Making sure that the properties are sane even when the ipv4 stack is set to disabled could prevent users to run into such issue,
which in my opinion has a potential to create more confusion, than failing immediately.


Version-Release number of selected component (if applicable):
nmstate-1.1.0-3.el8

nispor                         x86_64   1.2.2-1.el8          appstream   1.4 M
python3-libnmstate             noarch   1.1.0-3.el8          appstream   239 k
python3-nispor                 noarch   1.2.2-1.el8          appstream    39 k
NetworkManager                 x86_64   1:1.36.0-0.1.el8     baseos      2.3 M

How reproducible:
100%

Steps to Reproduce:
1. apply desiredState with ipv4.doesntexist property and ipv4.enabled: false
2. change ipv4.enabled to true
3.

Actual results:


Expected results:


Additional info: