[#3378] Fixed form logic trigger_from_step for copied form

Backport-of: #3478

src/openforms/forms/models/form.py

@@ -388,10 +388,16 @@ def copy(self):
 
             form_step.save()
 
-        for logic in self.formlogic_set.all():
+        for logic in self.formlogic_set.all().select_related("trigger_from_step"):
             logic.pk = None
             logic.uuid = _uuid.uuid4()
             logic.form = copy
+
+            if logic.trigger_from_step:
+                logic.trigger_from_step = logic.form.formstep_set.get(
+                    order=logic.trigger_from_step.order
+                )
+
             logic.save()
 
         FormVariable.objects.create_for_form(copy)

src/openforms/forms/tests/admin/test_form.py

@@ -549,6 +549,25 @@ def test_form_admin_copy(self):
         copied_form_step_form_definition = copied_form_step.form_definition
         self.assertEqual(copied_form_step_form_definition, form_step.form_definition)
 
+    @tag("gh-3378")
+    def test_copy_form_with_trigger_from_step_in_logic(self):
+        user = SuperUserFactory.create()
+        self.client.force_login(user)
+
+        form_step = FormStepFactory.create()
+        FormLogicFactory.create(form=form_step.form, trigger_from_step=form_step)
+
+        admin_url = reverse("admin:forms_form_change", args=(form_step.form.pk,))
+
+        # React UI renders this input, so simulate it in a raw POST call
+        self.client.post(admin_url, data={"_copy": "Copy"})
+
+        copied_form = Form.objects.exclude(pk=form_step.form.pk).get()
+        copied_step = FormStep.objects.exclude(pk=form_step.pk).get()
+        copied_logic = copied_form.formlogic_set.get()
+
+        self.assertEqual(copied_logic.trigger_from_step, copied_step)
+
 
 @disable_2fa
 class FormAdminActionsTests(FormListAjaxMixin, WebTest):