Use inheritance for IdentityForm

The previous composition version had some flaws due to multiple
instances of a given Field with different addresses when reinstalled in
the parent class. This caused the field validation validate_ to not work
as it was not taken the expected referenced values.

Instead of duplicating the code, we use an inherited version, taking and
overriding only our desired fields.

We still need to derive WSLIdentityView from the base class instead of
IdentityView, as this is what is instantiating the form.
(WSLIdentityForm instead of IdentityForm).

Co-authored-by: Jean-Baptiste Lallement <jean-baptiste@ubuntu.com>

system_setup/ui/views/identity.py

@@ -13,6 +13,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import os
 from urwid import (
     connect_signal,
     )
@@ -20,13 +21,14 @@ from urwid import (
 
 from subiquity.common.types import IdentityData
 from subiquity.ui.views.identity import IdentityForm, IdentityView, setup_password_validation
-from subiquitycore.ui.form import Form
 from subiquitycore.ui.utils import screen
 from subiquitycore.utils import crypt_password
 from subiquitycore.view import BaseView
 
+from subiquity.common.resources import resource_path
 
-class WSLIdentityForm(Form):
+
+class WSLIdentityForm(IdentityForm):
 
     realname = IdentityForm.realname
     username = IdentityForm.username
@@ -34,23 +36,6 @@ class WSLIdentityForm(Form):
     password = IdentityForm.password
     confirm_password = IdentityForm.confirm_password
 
-    def __init__(self, initial):
-        self.identityForm = IdentityForm([], initial)
-        super().__init__(initial=initial)
-
-    def validate_realname(self):
-        self.identityForm.validate_realname()
-
-    def validate_username(self):
-        self.identityForm.validate_username()
-
-    def validate_password(self):
-        self.identityForm.validate_password()
-
-    def validate_confirm_password(self):
-        self.identityForm.validate_confirm_password()
-
-
 class WSLIdentityView(BaseView):
     title = IdentityView.title
     excerpt = _("Please create a default UNIX user account. "
@@ -59,12 +44,25 @@ class WSLIdentityView(BaseView):
     def __init__(self, controller, identity_data):
         self.controller = controller
 
+        reserved_usernames_path = resource_path('reserved-usernames')
+        reserved_usernames = set()
+        if os.path.exists(reserved_usernames_path):
+            with open(reserved_usernames_path) as fp:
+                for line in fp:
+                    line = line.strip()
+                    if line.startswith('#') or not line:
+                        continue
+                    reserved_usernames.add(line)
+        else:
+            reserved_usernames.add('root')
+
         initial = {
             'realname': identity_data.realname,
             'username': identity_data.username,
             }
 
-        self.form = WSLIdentityForm(initial)
+        # This is the different form model with IdentityView which prevents us from inheriting it
+        self.form = WSLIdentityForm([], initial)
 
         connect_signal(self.form, 'submit', self.done)
         setup_password_validation(self.form, _("passwords"))