Hide qvm-prefs default value with --hide-default

fixes: QubesOS/qubes-issues#8615

qubesadmin/tests/tools/qvm_prefs.py

@@ -164,3 +164,17 @@ def test_008_set_vm_prop_none(self):
         self.assertEqual(0, qubesadmin.tools.qvm_prefs.main([
             'dom0', 'prop1', 'None'], app=self.app))
         self.assertAllCalled()
+
+    def test_009_hide_default(self):
+        self.app.expected_calls[
+            ('dom0', 'admin.vm.List', None, None)] = \
+            b'0\x00dom0 class=AdminVM state=Running\n' \
+            b'vm1 class=AppVM state=Stopped\n'
+        self.app.expected_calls[
+            ('dom0', 'admin.vm.property.Get', 'prop1', None)] = \
+            b'0\x00default=True type=vm vm1'
+        with qubesadmin.tests.tools.StdoutBuffer() as stdout:
+            qubesadmin.tools.qvm_prefs.main(['dom0', 'prop1', '--hide-default'],
+                                            app=self.app)
+        self.assertEqual('', stdout.getvalue())
+        self.assertAllCalled()

qubesadmin/tools/qvm_prefs.py

@@ -141,9 +141,12 @@ def process_actions(parser, args, target):
         return 0
 
     try:
-        value = getattr(target, args.property)
-        if value is not None:
-            print(str(value))
+        if target.property_is_default(args.property) and args.hide_default:
+            return 0
+        else:
+            value = getattr(target, args.property)
+            if value is not None:
+                print(str(value))
     except qubesadmin.exc.QubesNoSuchPropertyError:
         parser.error('no such property: {!r}'.format(args.property))
     except qubesadmin.exc.QubesException as e: