device: Delete existing print in EnrollStart

gnome-control-center expects to be able to re-enroll an existing print
when calling EnrollStart without deleting it first. As such, implicitly
delete the existing print rather than throwing an error.

Ideally, we'll change the API, but we need to give API users time to
adjust to the world.

src/device.c

@@ -54,6 +54,11 @@ static gboolean action_authorization_handler (GDBusInterfaceSkeleton *,
                                               GDBusMethodInvocation *,
                                               gpointer user_data);
 
+static gboolean delete_enrolled_fingers (FprintDevice *rdev,
+                                         const char   *user,
+                                         FpFinger      finger,
+                                         GError      **error);
+
 static GQuark quark_auth_user = 0;
 
 typedef enum {
@@ -1979,22 +1984,21 @@ fprint_device_enroll_start (FprintDBusDevice      *dbus_dev,
   store.print_data_load (priv->dev, finger,
                          session->username, &existing_print);
 
-  if (existing_print)
-    {
-      g_set_error (&error, FPRINT_ERROR, FPRINT_ERROR_FINGER_ALREADY_ENROLLED,
-                   "Finger %d has already been enrolled for user %s", finger, session->username);
-      g_dbus_method_invocation_return_gerror (invocation,
-                                              error);
-      return TRUE;
-    }
-
-
   if (!can_start_action (rdev, &error))
     {
       g_dbus_method_invocation_return_gerror (invocation, error);
       return TRUE;
     }
 
+  if (existing_print)
+    {
+      if (!delete_enrolled_fingers (rdev, session->username, finger, &error))
+        {
+          g_dbus_method_invocation_return_gerror (invocation, error);
+          return TRUE;
+        }
+    }
+
   g_debug ("start enrollment device %d finger %d", priv->id, finger);
 
   priv->current_cancellable = g_cancellable_new ();

tests/fprintd.py

@@ -2315,9 +2315,21 @@ class FPrintdVirtualDeviceEnrollTests(FPrintdVirtualDeviceBaseTest):
     def test_enroll_already_enrolled_finger(self):
         self.enroll_image('whorl', start=False)
 
-        self.stop_on_teardown = False
+        # We can enroll a new image deleting the first
-        with self.assertFprintError('FingerAlreadyEnrolled'):
         self.device.EnrollStart('(s)', 'left-middle-finger')
+        self.enroll_image('arch', start=False)
+        self.stop_on_teardown = False
+
+        # If we verify, 'arch' will match, 'whorl' will not match
+        self.device.VerifyStart('(s)', 'any')
+        self.send_image('whorl')
+        self.assertVerifyNoMatch()
+        self.device.VerifyStop()
+
+        self.device.VerifyStart('(s)', 'any')
+        self.send_image('arch')
+        self.assertVerifyMatch()
+        self.device.VerifyStop()
 
     def test_enroll_duplicate_image(self):
         self.enroll_image('whorl', finger='left-thumb', start=False)