[1.7.x] Fixed #23405 -- Fixed makemigrations prompt when adding Text/CharField.

A default is no longer required.

Backport of d8f3b86a76 from master

django/db/migrations/autodetector.py

@@ -802,8 +802,11 @@ class MigrationAutodetector(object):
                         None,
                         True
                     ))
-            # You can't just add NOT NULL fields with no default
-            if not field.null and not field.has_default() and not isinstance(field, models.ManyToManyField):
+            # You can't just add NOT NULL fields with no default or fields
+            # which don't allow empty strings as default.
+            if (not field.null and not field.has_default() and
+                    not isinstance(field, models.ManyToManyField) and
+                    not (field.blank and field.empty_strings_allowed)):
                 field = field.clone()
                 field.default = self.questioner.ask_not_null_addition(field_name, model_name)
                 self.add_operation(

docs/releases/1.7.2.txt

@@ -140,3 +140,6 @@ Bugfixes
   a user specified ``default``. For example, a ``CharField`` with ``blank=True``
   didn't set existing rows to an empty string which resulted in a crash when
   adding the ``NOT NULL`` constraint (:ticket:`23987`).
+
+* ``makemigrations`` no longer prompts for a default value when adding
+  ``TextField()`` or ``CharField()`` without a ``default`` (:ticket:`23405`).

tests/migrations/test_autodetector.py

@@ -54,6 +54,16 @@ class AutodetectorTests(TestCase):
         ("name", models.CharField(max_length=200, default=DeconstructableObject())),
     ])
     author_custom_pk = ModelState("testapp", "Author", [("pk_field", models.IntegerField(primary_key=True))])
+    author_with_biography_non_blank = ModelState("testapp", "Author", [
+        ("id", models.AutoField(primary_key=True)),
+        ("name", models.CharField()),
+        ("biography", models.TextField()),
+    ])
+    author_with_biography_blank = ModelState("testapp", "Author", [
+        ("id", models.AutoField(primary_key=True)),
+        ("name", models.CharField(blank=True)),
+        ("biography", models.TextField(blank=True)),
+    ])
     author_with_book = ModelState("testapp", "Author", [
         ("id", models.AutoField(primary_key=True)),
         ("name", models.CharField(max_length=200)),
@@ -1641,3 +1651,44 @@ class AutodetectorTests(TestCase):
         self.assertNumberMigrations(changes, 'a', 1)
         self.assertOperationTypes(changes, 'a', 0, ["CreateModel"])
         self.assertMigrationDependencies(changes, 'a', 0, [])
+
+    def test_add_blank_textfield_and_charfield(self):
+        """
+        #23405 - Adding a NOT NULL and blank `CharField` or `TextField`
+        without default should not prompt for a default.
+        """
+        class CustomQuestioner(MigrationQuestioner):
+            def ask_not_null_addition(self, field_name, model_name):
+                raise Exception("Should not have prompted for not null addition")
+
+        before = self.make_project_state([self.author_empty])
+        after = self.make_project_state([self.author_with_biography_blank])
+        autodetector = MigrationAutodetector(before, after, CustomQuestioner())
+        changes = autodetector._detect_changes()
+        self.assertNumberMigrations(changes, 'testapp', 1)
+        self.assertOperationTypes(changes, 'testapp', 0, ["AddField", "AddField"])
+        self.assertOperationAttributes(changes, 'testapp', 0, 0)
+
+    def test_add_non_blank_textfield_and_charfield(self):
+        """
+        #23405 - Adding a NOT NULL and non-blank `CharField` or `TextField`
+        without default should prompt for a default.
+        """
+        class CustomQuestioner(MigrationQuestioner):
+            def __init__(self):
+                super(CustomQuestioner, self).__init__()
+                self.ask_method_call_count = 0
+
+            def ask_not_null_addition(self, field_name, model_name):
+                self.ask_method_call_count += 1
+
+        before = self.make_project_state([self.author_empty])
+        after = self.make_project_state([self.author_with_biography_non_blank])
+        questioner_instance = CustomQuestioner()
+        autodetector = MigrationAutodetector(before, after, questioner_instance)
+        changes = autodetector._detect_changes()
+        # need to check for questioner call count
+        self.assertEqual(questioner_instance.ask_method_call_count, 2)
+        self.assertNumberMigrations(changes, 'testapp', 1)
+        self.assertOperationTypes(changes, 'testapp', 0, ["AddField", "AddField"])
+        self.assertOperationAttributes(changes, 'testapp', 0, 0)