[1.7.x] Fixed #22791 -- Invoke interactive questioner only for conflicts in specified apps.

Thanks bendavis78 for the report and Tim Graham for the review.

Backport of f7a78f9bba from master

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0001_initial.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    operations = [
+
+        migrations.CreateModel(
+            "Author",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+
+        migrations.CreateModel(
+            "Tribble",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("fluffy", models.BooleanField(default=True)),
+            ],
+        )
+
+    ]

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0002_conflicting_second.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("unspecified_app_with_conflict", "0001_initial")]
+
+    operations = [
+
+        migrations.CreateModel(
+            "Something",
+            [
+                ("id", models.AutoField(primary_key=True)),
+            ],
+        )
+
+    ]

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0002_second.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("unspecified_app_with_conflict", "0001_initial")]
+
+    operations = [
+
+        migrations.DeleteModel("Tribble"),
+
+        migrations.RemoveField("Author", "silly_field"),
+
+        migrations.AddField("Author", "rating", models.IntegerField(default=0)),
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+            ],
+        )
+
+    ]

tests/migrations/test_commands.py

@@ -493,3 +493,49 @@ class MakeMigrationsTests(MigrationTestBase):
             if os.path.exists(merge_file):
                 os.remove(merge_file)
         self.assertNotIn("Created new merge migration", stdout.getvalue())
+
+    @override_system_checks([])
+    @override_settings(
+        MIGRATION_MODULES={"migrations": "migrations.test_migrations_no_changes"},
+        INSTALLED_APPS=[
+            "migrations",
+            "migrations.migrations_test_apps.unspecified_app_with_conflict"])
+    def test_makemigrations_unspecified_app_with_conflict_no_merge(self):
+        """
+        Makes sure that makemigrations does not raise a CommandError when an
+        unspecified app has conflicting migrations.
+        """
+        try:
+            call_command("makemigrations", "migrations", merge=False, verbosity=0)
+        except CommandError:
+            self.fail("Makemigrations fails resolving conflicts in an unspecified app")
+
+    @override_system_checks([])
+    @override_settings(
+        INSTALLED_APPS=[
+            "migrations.migrations_test_apps.migrated_app",
+            "migrations.migrations_test_apps.unspecified_app_with_conflict"])
+    def test_makemigrations_unspecified_app_with_conflict_merge(self):
+        """
+        Makes sure that makemigrations does not create a merge for an
+        unspecified app even if it has conflicting migrations.
+        """
+        # Monkeypatch interactive questioner to auto accept
+        old_input = questioner.input
+        questioner.input = lambda _: "y"
+        stdout = six.StringIO()
+        merge_file = os.path.join(self.test_dir,
+                                  'migrations_test_apps',
+                                  'unspecified_app_with_conflict',
+                                  'migrations',
+                                  '0003_merge.py')
+        try:
+            call_command("makemigrations", "migrated_app", merge=True, interactive=True, stdout=stdout)
+            self.assertFalse(os.path.exists(merge_file))
+            self.assertIn("No conflicts detected to merge.", stdout.getvalue())
+        except CommandError:
+            self.fail("Makemigrations fails resolving conflicts in an unspecified app")
+        finally:
+            questioner.input = old_input
+            if os.path.exists(merge_file):
+                os.remove(merge_file)