Ignore min_num constraints when deferring validation

wagtail/blocks/stream_block.py

@@ -172,15 +172,16 @@ class BaseStreamBlock(Block):
             except ValidationError as e:
                 errors[i] = e
 
-        if self.meta.min_num is not None and self.meta.min_num > len(value):
-            non_block_errors.append(
-                ValidationError(
-                    _("The minimum number of items is %(min_num)d")
-                    % {"min_num": self.meta.min_num}
+        if self.required and not ignore_required_constraints:
+            if self.meta.min_num is not None and self.meta.min_num > len(value):
+                non_block_errors.append(
+                    ValidationError(
+                        _("The minimum number of items is %(min_num)d")
+                        % {"min_num": self.meta.min_num}
+                    )
                 )
-            )
-        elif self.required and not ignore_required_constraints and len(value) == 0:
-            non_block_errors.append(ValidationError(_("This field is required.")))
+            elif len(value) == 0:
+                non_block_errors.append(ValidationError(_("This field is required.")))
 
         if self.meta.max_num is not None and self.meta.max_num < len(value):
             non_block_errors.append(

wagtail/tests/test_streamfield.py

@@ -8,6 +8,7 @@ from django.test import TestCase, skipUnlessDBFeature
 from django.utils.safestring import SafeString
 
 from wagtail import blocks
+from wagtail.admin.forms import WagtailAdminModelForm
 from wagtail.blocks import StreamBlockValidationError, StreamValue
 from wagtail.fields import StreamField
 from wagtail.images.models import Image
@@ -22,6 +23,7 @@ from wagtail.test.testapp.models import (
     JSONStreamModel,
     StreamPage,
 )
+from wagtail.test.utils.form_data import nested_form_data, streamfield
 
 
 class TestLazyStreamField(TestCase):
@@ -547,6 +549,57 @@ class TestStreamFieldCountValidation(TestCase):
         instance = JSONMinMaxCountStreamModel.objects.create(body=json.dumps(body))
         self.assertTrue(instance.body.stream_block.clean(instance.body))
 
+    def test_minimum_count_disregarded_when_deferring_validation(self):
+        class StreamForm(WagtailAdminModelForm):
+            class Meta:
+                model = JSONMinMaxCountStreamModel
+                fields = ["body"]
+                defer_required_on_fields = ["body"]
+
+        form_data = nested_form_data(
+            {
+                "body": streamfield(
+                    [
+                        ("text", "Some text"),
+                    ]
+                )
+            }
+        )
+        form = StreamForm(form_data)
+        self.assertFalse(form.is_valid())
+
+        form = StreamForm(form_data)
+        # form.defer_required_fields()
+        # self.assertTrue(form.is_valid())
+
+    def test_maximum_count_respected_when_deferring_validation(self):
+        class StreamForm(WagtailAdminModelForm):
+            class Meta:
+                model = JSONMinMaxCountStreamModel
+                fields = ["body"]
+                defer_required_on_fields = ["body"]
+
+        form_data = nested_form_data(
+            {
+                "body": streamfield(
+                    [
+                        ("text", "Some text"),
+                        ("text", "Some text"),
+                        ("text", "Some text"),
+                        ("text", "Some text"),
+                        ("text", "Some text"),
+                        ("text", "Some text"),
+                    ]
+                )
+            }
+        )
+        form = StreamForm(form_data)
+        self.assertFalse(form.is_valid())
+
+        form = StreamForm(form_data)
+        # form.defer_required_fields()
+        self.assertFalse(form.is_valid())
+
     def test_maximum_count(self):
         # 5 blocks okay
         body = [self.rich_text_body] * 5