From d57124433f0d0f2bf61ea4e14962f3b663ab20c7 Mon Sep 17 00:00:00 2001
From: Tim Graham <timograham@gmail.com>
Date: Thu, 4 Dec 2014 09:11:30 -0500
Subject: [PATCH] [1.7.x] Fixed #23920 -- Fixed MySQL crash when adding
 blank=True to TextField.

Thanks wkornewald for the report and Markus Holtermann for review.

Backport of 765fa36d57d08d0568438f6fd74521e7a56abb61 from master
---
 django/db/backends/schema.py |  2 +-
 docs/releases/1.7.2.txt      |  5 ++++-
 tests/schema/models.py       |  4 ++++
 tests/schema/tests.py        | 15 ++++++++++++++-
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/django/db/backends/schema.py b/django/db/backends/schema.py
index 4fc6601dfd..06d7ad27bf 100644
--- a/django/db/backends/schema.py
+++ b/django/db/backends/schema.py
@@ -560,7 +560,7 @@ class BaseDatabaseSchemaEditor(object):
         # Default change?
         old_default = self.effective_default(old_field)
         new_default = self.effective_default(new_field)
-        if old_default != new_default:
+        if old_default != new_default and not self.skip_default(new_field):
             if new_default is None:
                 actions.append((
                     self.sql_alter_column_no_default % {
diff --git a/docs/releases/1.7.2.txt b/docs/releases/1.7.2.txt
index 771e353818..e3db0d404e 100644
--- a/docs/releases/1.7.2.txt
+++ b/docs/releases/1.7.2.txt
@@ -107,4 +107,7 @@ Bugfixes
 
 * Prevented the
   :class:`~django.contrib.auth.middleware.SessionAuthenticationMiddleware` from
-  setting a ``"Vary: Cookie"`` header on all responses.
+  setting a ``"Vary: Cookie"`` header on all responses (:ticket:`23939`).
+
+* Fixed a crash when adding ``blank=True`` to ``TextField()`` on MySQL
+  (:ticket:`23920`).
diff --git a/tests/schema/models.py b/tests/schema/models.py
index 3139838b97..df8a1c5ce4 100644
--- a/tests/schema/models.py
+++ b/tests/schema/models.py
@@ -171,3 +171,7 @@ class Thing(models.Model):
 
     def __str__(self):
         return self.when
+
+
+class Note(models.Model):
+    info = models.TextField()
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 4a7d537665..4c773599f9 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -10,7 +10,7 @@ from django.db.transaction import atomic
 from .models import (Author, AuthorWithDefaultHeight, AuthorWithM2M, Book, BookWithLongName,
     BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename,
     UniqueTest, Thing, TagThrough, BookWithM2MThrough, AuthorTag, AuthorWithM2MThrough,
-    AuthorWithEvenLongerName, BookWeak)
+    AuthorWithEvenLongerName, BookWeak, Note)
 
 
 class SchemaTests(TransactionTestCase):
@@ -423,6 +423,19 @@ class SchemaTests(TransactionTestCase):
         self.assertEqual(columns['name'][0], "TextField")
         self.assertEqual(bool(columns['name'][1][6]), False)
 
+    def test_alter_text_field(self):
+        # Regression for "BLOB/TEXT column 'info' can't have a default value")
+        # on MySQL.
+        new_field = TextField(blank=True)
+        new_field.set_attributes_from_name("info")
+        with connection.schema_editor() as editor:
+            editor.alter_field(
+                Note,
+                Note._meta.get_field_by_name("info")[0],
+                new_field,
+                strict=True,
+            )
+
     def test_alter_null_to_not_null(self):
         """
         #23609 - Tests handling of default values when altering from NULL to NOT NULL.