From 3fa5eb125cac752ce46362bad31484c874498b43 Mon Sep 17 00:00:00 2001
From: Matt Westcott <matt@west.co.tt>
Date: Fri, 8 Jul 2022 18:40:07 +0100
Subject: [PATCH] Implement max_length validation on RichTextBlock

---
 docs/reference/streamfield/blocks.md |  1 +
 wagtail/blocks/field_block.py        | 11 ++++++++++-
 wagtail/tests/test_blocks.py         | 14 ++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/docs/reference/streamfield/blocks.md b/docs/reference/streamfield/blocks.md
index 011df6c111..6fe66cac5a 100644
--- a/docs/reference/streamfield/blocks.md
+++ b/docs/reference/streamfield/blocks.md
@@ -205,6 +205,7 @@ All block definitions accept the following optional keyword arguments:
    :param editor: The rich text editor to be used (see :ref:`WAGTAILADMIN_RICH_TEXT_EDITORS`).
    :param features: Specifies the set of features allowed (see :ref:`rich_text_features`).
    :param required: If true (the default), the field cannot be left blank.
+   :param max_length: The maximum allowed length of the field. Only text is counted; rich text formatting and embedded content does not count towards the limit.
    :param help_text: Help text to display alongside the field.
    :param validators: A list of validation functions for the field (see `Django Validators <https://docs.djangoproject.com/en/stable/ref/validators/>`__).
    :param form_classname: A value to add to the form field's ``class`` attribute when rendered on the page editing form.
diff --git a/wagtail/blocks/field_block.py b/wagtail/blocks/field_block.py
index ee9e7b4e90..702235aa1b 100644
--- a/wagtail/blocks/field_block.py
+++ b/wagtail/blocks/field_block.py
@@ -13,7 +13,11 @@ from django.utils.translation import gettext as _
 
 from wagtail.admin.staticfiles import versioned_static
 from wagtail.coreutils import camelcase_to_underscore, resolve_model_string
-from wagtail.rich_text import RichText, get_text_for_indexing
+from wagtail.rich_text import (
+    RichText,
+    RichTextMaxLengthValidator,
+    get_text_for_indexing,
+)
 from wagtail.telepath import Adapter, register
 
 from .base import Block
@@ -642,9 +646,14 @@ class RichTextBlock(FieldBlock):
         help_text=None,
         editor="default",
         features=None,
+        max_length=None,
         validators=(),
         **kwargs,
     ):
+        if max_length is not None:
+            validators = list(validators) + [
+                RichTextMaxLengthValidator(max_length),
+            ]
         self.field_options = {
             "required": required,
             "help_text": help_text,
diff --git a/wagtail/tests/test_blocks.py b/wagtail/tests/test_blocks.py
index 67ecf00b15..f869bc4a87 100644
--- a/wagtail/tests/test_blocks.py
+++ b/wagtail/tests/test_blocks.py
@@ -629,6 +629,20 @@ class TestRichTextBlock(TestCase):
         with self.assertRaises(ValidationError):
             block.clean(RichText("<p>bar</p>"))
 
+    def test_validate_max_length(self):
+        block = blocks.RichTextBlock(max_length=20)
+
+        block.clean(RichText("<p>short</p>"))
+
+        with self.assertRaises(ValidationError):
+            block.clean(RichText("<p>this exceeds the 20 character limit</p>"))
+
+        block.clean(
+            RichText(
+                '<p><a href="http://really-long-domain-name.example.com">also</a> short</p>'
+            )
+        )
+
     def test_get_searchable_content(self):
         block = blocks.RichTextBlock()
         value = RichText(