Defer validation of required text fields in previews

wagtail/admin/tests/pages/test_preview.py

@@ -264,6 +264,53 @@ class TestPreview(WagtailTestUtils, TestCase):
         self.assertContains(response, "<li>Parties</li>")
         self.assertContains(response, "<li>Holidays</li>")
 
+    def test_preview_on_create_with_deferred_required_fields(self):
+        preview_url = reverse(
+            "wagtailadmin_pages:preview_on_add",
+            args=("tests", "eventpage", self.home_page.id),
+        )
+
+        preview_session_key = "wagtail-preview-tests-eventpage-{}".format(
+            self.home_page.id
+        )
+        self.assertNotIn(preview_session_key, self.client.session)
+
+        response = self.client.post(
+            preview_url,
+            {
+                "title": "Bare minimum",
+                "slug": "bare-minimum",
+                "carousel_items-TOTAL_FORMS": 0,
+                "carousel_items-INITIAL_FORMS": 0,
+                "speakers-TOTAL_FORMS": 0,
+                "speakers-INITIAL_FORMS": 0,
+                "related_links-TOTAL_FORMS": 0,
+                "related_links-INITIAL_FORMS": 0,
+                "head_counts-TOTAL_FORMS": 0,
+                "head_counts-INITIAL_FORMS": 0,
+            },
+        )
+
+        # Check the JSON response
+        self.assertEqual(response.status_code, 200)
+        self.assertJSONEqual(
+            response.content.decode(),
+            {"is_valid": True, "is_available": True},
+        )
+
+        # Check the user can refresh the preview
+        preview_session_key = "wagtail-preview-tests-eventpage-{}".format(
+            self.home_page.id
+        )
+        self.assertIn(preview_session_key, self.client.session)
+
+        response = self.client.get(preview_url)
+
+        # Check the HTML response
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, "tests/event_page.html")
+        self.assertContains(response, "Bare minimum")
+
     def test_preview_on_edit_with_m2m_field(self):
         preview_url = reverse(
             "wagtailadmin_pages:preview_on_edit", args=(self.event_page.id,)
@@ -354,6 +401,45 @@ class TestPreview(WagtailTestUtils, TestCase):
         self.assertContains(response, "<li>Parties</li>")
         self.assertContains(response, "<li>Holidays</li>")
 
+    def test_preview_on_edit_with_deferred_required_fields(self):
+        preview_url = reverse(
+            "wagtailadmin_pages:preview_on_edit", args=(self.event_page.id,)
+        )
+
+        response = self.client.post(
+            preview_url,
+            {
+                "title": "Bare minimum",
+                "slug": "bare-minimum",
+                "carousel_items-TOTAL_FORMS": 0,
+                "carousel_items-INITIAL_FORMS": 0,
+                "speakers-TOTAL_FORMS": 0,
+                "speakers-INITIAL_FORMS": 0,
+                "related_links-TOTAL_FORMS": 0,
+                "related_links-INITIAL_FORMS": 0,
+                "head_counts-TOTAL_FORMS": 0,
+                "head_counts-INITIAL_FORMS": 0,
+            },
+        )
+
+        # Check the JSON response
+        self.assertEqual(response.status_code, 200)
+        self.assertJSONEqual(
+            response.content.decode(),
+            {"is_valid": True, "is_available": True},
+        )
+
+        # Check the user can refresh the preview
+        preview_session_key = f"wagtail-preview-{self.event_page.id}"
+        self.assertIn(preview_session_key, self.client.session)
+
+        response = self.client.get(preview_url)
+
+        # Check the HTML response
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, "tests/event_page.html")
+        self.assertContains(response, "Bare minimum")
+
     def test_preview_on_edit_expiry(self):
         initial_datetime = timezone.now()
         expiry_datetime = initial_datetime + datetime.timedelta(

wagtail/admin/views/generic/preview.py

@@ -11,6 +11,7 @@ from django.utils.functional import cached_property
 from django.utils.translation import gettext
 from django.views.generic import TemplateView, View
 
+from wagtail.admin.forms.models import WagtailAdminModelForm
 from wagtail.admin.panels import get_edit_handler
 from wagtail.blocks.base import Block
 from wagtail.models import PreviewableMixin, RevisionMixin
@@ -77,10 +78,15 @@ class PreviewOnEdit(View):
             post_data = ""
         return QueryDict(post_data)
 
+    def validate_form(self, form):
+        if isinstance(form, WagtailAdminModelForm):
+            form.defer_required_fields()
+        return form.is_valid()
+
     def post(self, request, *args, **kwargs):
         self.remove_old_preview_data()
         form = self.get_form(request.POST)
-        is_valid = form.is_valid()
+        is_valid = self.validate_form(form)
 
         if is_valid:
             # TODO: Handle request.FILES.
@@ -89,7 +95,7 @@ class PreviewOnEdit(View):
         else:
             # Check previous data in session to determine preview availability
             form = self.get_form(self._get_data_from_session())
-            is_available = form.is_valid()
+            is_available = self.validate_form(form)
 
         return JsonResponse({"is_valid": is_valid, "is_available": is_available})
 
@@ -104,7 +110,7 @@ class PreviewOnEdit(View):
     def get(self, request, *args, **kwargs):
         form = self.get_form(self._get_data_from_session())
 
-        if not form.is_valid():
+        if not self.validate_form(form):
             return self.error_response()
 
         form.save(commit=False)

wagtail/admin/views/pages/preview.py

@@ -95,9 +95,9 @@ class PreviewOnCreate(PreviewOnEdit):
 
     def get_form(self, query_dict):
         form = super().get_form(query_dict)
-        if form.is_valid():
+        if self.validate_form(form):
             # Ensures our unsaved page has a suitable url.
             form.instance.set_url_path(form.parent_page)
 
-            form.instance.full_clean()
+            form.instance.minimal_clean()
         return form

wagtail/snippets/tests/test_preview.py

@@ -65,7 +65,7 @@ class TestPreview(WagtailTestUtils, TestCase):
     def test_preview_on_create_with_invalid_data(self):
         self.assertNotIn(self.session_key_prefix, self.client.session)
 
-        response = self.client.post(self.preview_on_add_url, {"text": ""})
+        response = self.client.post(self.preview_on_add_url, {"categories": [999999]})
 
         # Check the JSON response
         self.assertEqual(response.status_code, 200)
@@ -116,6 +116,36 @@ class TestPreview(WagtailTestUtils, TestCase):
         self.assertContains(response, "<li>Parties</li>")
         self.assertContains(response, "<li>Holidays</li>")
 
+    def test_preview_on_create_with_deferred_required_fields(self):
+        response = self.client.post(
+            self.preview_on_add_url,
+            {"categories": [self.holidays_category.id]},
+        )
+
+        # Check the JSON response
+        self.assertEqual(response.status_code, 200)
+        self.assertJSONEqual(
+            response.content.decode(),
+            {"is_valid": True, "is_available": True},
+        )
+
+        # Check the user can refresh the preview
+        self.assertIn(self.session_key_prefix, self.client.session)
+
+        response = self.client.get(self.preview_on_add_url)
+
+        # Check the HTML response
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, "tests/previewable_model.html")
+
+        # The text is empty
+        self.assertContains(response, "<title>(Default Preview)</title>", html=True)
+        self.assertContains(response, "<h1></h1>", html=True)
+
+        # The category is Holidays (only)
+        self.assertNotContains(response, "<li>Parties</li>")
+        self.assertContains(response, "<li>Holidays</li>")
+
     def test_preview_on_edit_with_m2m_field(self):
         response = self.client.post(self.preview_on_edit_url, self.post_data)
 
@@ -150,7 +180,7 @@ class TestPreview(WagtailTestUtils, TestCase):
 
         # Send an invalid update request
         response = self.client.post(
-            self.preview_on_edit_url, {**self.post_data, "text": ""}
+            self.preview_on_edit_url, {**self.post_data, "categories": [999999]}
         )
         self.assertEqual(response.status_code, 200)
         self.assertJSONEqual(
@@ -170,6 +200,36 @@ class TestPreview(WagtailTestUtils, TestCase):
         self.assertContains(response, "<li>Parties</li>")
         self.assertContains(response, "<li>Holidays</li>")
 
+    def test_preview_on_edit_with_deferred_required_fields(self):
+        response = self.client.post(
+            self.preview_on_edit_url,
+            {"categories": [self.holidays_category.id]},
+        )
+
+        # Check the JSON response
+        self.assertEqual(response.status_code, 200)
+        self.assertJSONEqual(
+            response.content.decode(),
+            {"is_valid": True, "is_available": True},
+        )
+
+        # Check the user can refresh the preview
+        self.assertIn(self.edit_session_key, self.client.session)
+
+        response = self.client.get(self.preview_on_edit_url)
+
+        # Check the HTML response
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, "tests/previewable_model.html")
+
+        # The text is empty
+        self.assertContains(response, "<title>(Default Preview)</title>", html=True)
+        self.assertContains(response, "<h1></h1>", html=True)
+
+        # The category is Holidays (only)
+        self.assertNotContains(response, "<li>Parties</li>")
+        self.assertContains(response, "<li>Holidays</li>")
+
     def test_preview_on_edit_expiry(self):
         initial_datetime = timezone.now()
         expiry_datetime = initial_datetime + datetime.timedelta(