Fixed #31144 -- Relaxed system check for max_length of CharFields on MySQL/MariaDB by turning into a warning.

2 files changed, 11 insertions, 3 deletions

diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 5f9f9301ed..2ebaf5201f 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -127,9 +127,12 @@ MySQL and MariaDB
 If you're using MySQL or MariaDB, the following checks will be performed:
 
 * **mysql.E001**: MySQL/MariaDB does not allow unique ``CharField``\s to have a
-  ``max_length`` > 255.
+  ``max_length`` > 255. *This check was changed to* ``mysql.W003`` *in Django
+  3.1 as the real maximum size depends on many factors.*
 * **mysql.W002**: MySQL/MariaDB Strict Mode is not set for database connection
   '<alias>'. See also :ref:`mysql-sql-mode`.
+* **mysql.W003**: MySQL/MariaDB may not allow unique ``CharField``\s to have a
+  ``max_length`` > 255.
 
 Model fields
 ------------
diff --git a/docs/ref/databases.txt b/docs/ref/databases.txt
index f61158c191..4d4a7d2aa9 100644
--- a/docs/ref/databases.txt
+++ b/docs/ref/databases.txt
@@ -581,13 +581,18 @@ these methods in no-op's based in the results of such detection.
 Notes on specific fields
 ------------------------
 
+.. _mysql-character-fields:
+
 Character fields
 ~~~~~~~~~~~~~~~~
 
-Any fields that are stored with ``VARCHAR`` column types have their
+Any fields that are stored with ``VARCHAR`` column types may have their
 ``max_length`` restricted to 255 characters if you are using ``unique=True``
 for the field. This affects :class:`~django.db.models.CharField`,
-:class:`~django.db.models.SlugField`.
+:class:`~django.db.models.SlugField`. See `the MySQL documentation`_ for more
+details.
+
+.. _the MySQL documentation: https://dev.mysql.com/doc/refman/en/create-index.html#create-index-column-prefixes
 
 ``TextField`` limitations
 ~~~~~~~~~~~~~~~~~~~~~~~~~