Better unique validation errors

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

registration/forms.py

@@ -82,6 +82,15 @@ class UserForm(forms.ModelForm):
         self.fields["last_name"].required = True
         self.fields["email"].required = True
 
+    def clean_email(self):
+        """
+        Ensure that the email address is unique.
+        """
+        email = self.data["email"]
+        if User.objects.filter(email=email).exclude(pk=self.instance.pk).exists():
+            self.add_error("email", _("This email address is already used."))
+        return email
+
     class Meta:
         model = User
         fields = ('first_name', 'last_name', 'email',)