[1.7.x] Fixed #22676 -- makemigrations --dry-run should not ask for defaults

Made the fix in InteractiveMigrationQuestioner class code, rather than
MigrationAutodetector, because --dry-run shouldn't affect whether
MigrationAutodetector will detect non-nullable fields, but the
questioner should skip the question and returns a None for default
(since that won't be used anyway) if --dry-run is used.

Backport of ee14961a2a from master

django/core/management/commands/makemigrations.py

@@ -77,7 +77,7 @@ class Command(BaseCommand):
         autodetector = MigrationAutodetector(
             loader.project_state(),
             ProjectState.from_apps(apps),
-            InteractiveMigrationQuestioner(specified_apps=app_labels),
+            InteractiveMigrationQuestioner(specified_apps=app_labels, dry_run=self.dry_run),
         )
 
         # If they want to make an empty migration, make one for each app

django/db/migrations/questioner.py

@@ -18,9 +18,10 @@ class MigrationQuestioner(object):
     interactive subclass is what the command-line arguments will use.
     """
 
-    def __init__(self, defaults=None, specified_apps=None):
+    def __init__(self, defaults=None, specified_apps=None, dry_run=None):
         self.defaults = defaults or {}
         self.specified_apps = specified_apps or set()
+        self.dry_run = dry_run
 
     def ask_initial(self, app_label):
         "Should we create an initial migration for the app?"
@@ -93,37 +94,39 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
 
     def ask_not_null_addition(self, field_name, model_name):
         "Adding a NOT NULL field to a model"
-        choice = self._choice_input(
-            "You are trying to add a non-nullable field '%s' to %s without a default;\n" % (field_name, model_name) +
-            "we can't do that (the database needs something to populate existing rows).\n" +
-            "Please select a fix:",
-            [
-                "Provide a one-off default now (will be set on all existing rows)",
-                "Quit, and let me add a default in models.py",
-            ]
-        )
-        if choice == 2:
-            sys.exit(3)
-        else:
-            print("Please enter the default value now, as valid Python")
-            print("The datetime module is available, so you can do e.g. datetime.date.today()")
-            while True:
-                if six.PY3:
-                    # Six does not correctly abstract over the fact that
-                    # py3 input returns a unicode string, while py2 raw_input
-                    # returns a bytestring.
-                    code = input(">>> ")
-                else:
-                    code = input(">>> ").decode(sys.stdin.encoding)
-                if not code:
-                    print("Please enter some code, or 'exit' (with no quotes) to exit.")
-                elif code == "exit":
-                    sys.exit(1)
-                else:
-                    try:
-                        return eval(code, {}, {"datetime": datetime_safe})
-                    except (SyntaxError, NameError) as e:
-                        print("Invalid input: %s" % e)
+        if not self.dry_run:
+            choice = self._choice_input(
+                "You are trying to add a non-nullable field '%s' to %s without a default;\n" % (field_name, model_name) +
+                "we can't do that (the database needs something to populate existing rows).\n" +
+                "Please select a fix:",
+                [
+                    "Provide a one-off default now (will be set on all existing rows)",
+                    "Quit, and let me add a default in models.py",
+                ]
+            )
+            if choice == 2:
+                sys.exit(3)
+            else:
+                print("Please enter the default value now, as valid Python")
+                print("The datetime module is available, so you can do e.g. datetime.date.today()")
+                while True:
+                    if six.PY3:
+                        # Six does not correctly abstract over the fact that
+                        # py3 input returns a unicode string, while py2 raw_input
+                        # returns a bytestring.
+                        code = input(">>> ")
+                    else:
+                        code = input(">>> ").decode(sys.stdin.encoding)
+                    if not code:
+                        print("Please enter some code, or 'exit' (with no quotes) to exit.")
+                    elif code == "exit":
+                        sys.exit(1)
+                    else:
+                        try:
+                            return eval(code, {}, {"datetime": datetime_safe})
+                        except (SyntaxError, NameError) as e:
+                            print("Invalid input: %s" % e)
+        return None
 
     def ask_rename(self, model_name, old_name, new_name, field_instance):
         "Was this field really renamed?"

tests/migrations/test_commands.py

@@ -6,6 +6,7 @@ import os
 import shutil
 
 from django.apps import apps
+from django.db import models
 from django.core.management import call_command, CommandError
 from django.db.migrations import questioner
 from django.test import override_settings, override_system_checks
@@ -362,3 +363,22 @@ class MakeMigrationsTests(MigrationTestBase):
         self.assertIn("Merging migrations", stdout.getvalue())
         self.assertIn("Branch 0002_second", stdout.getvalue())
         self.assertIn("Branch 0002_conflicting_second", stdout.getvalue())
+
+    @override_system_checks([])
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_no_default"})
+    def test_makemigrations_dry_run(self):
+        """
+        Ticket #22676 -- `makemigrations --dry-run` should not ask for defaults.
+        """
+
+        class SillyModel(models.Model):
+            silly_field = models.BooleanField(default=False)
+            silly_date = models.DateField()  # Added field without a default
+
+            class Meta:
+                app_label = "migrations"
+
+        stdout = six.StringIO()
+        call_command("makemigrations", "migrations", dry_run=True, stdout=stdout)
+        # Output the expected changes directly, without asking for defaults
+        self.assertIn("Add field silly_date to sillymodel", stdout.getvalue())

tests/migrations/test_migrations_no_default/0001_initial.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SillyModel',
+            fields=[
+                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
+                ('silly_field', models.BooleanField(default=False)),
+            ],
+            options={
+            },
+            bases=(models.Model,),
+        ),
+    ]