Use checksum type of a package for publication if it's not configured.

CHANGES/8725.bugfix

@@ -0,0 +1,4 @@
+Ensure a checksum type of a package is used for publications when a checksum type was not explicitly configured in Pulp 2.
+
+If you plan to perform sync from the migrated Pulp 3 to a Pulp 2 instance, this fix is important, otherwise you can ignore it.
+If you've already started migration of the RPM plugin to Pulp 3, reset the migration for it and start again.

pulp_2to3_migration/app/plugin/rpm/repository.py

@@ -71,8 +71,21 @@ def migrate_to_pulp3(cls, pulp2distributor, repo_version):
             pulp2_checksum_type = pulp2_config.get('checksum_type')
             checksum_types = None
             if pulp2_checksum_type:
-                checksum_types = {'metadata': pulp2_checksum_type,
-                                  'package': pulp2_checksum_type}
+                checksum_types = {
+                    'metadata': pulp2_checksum_type,
+                    'package': pulp2_checksum_type
+                }
+            else:
+                # Set the checksum type based on content in a repo, pulp 2 supports only one
+                # checksum type for packages in a repo. It is important to set checksum type for
+                # Pulp 3 to Pulp 2 sync use case.
+                package_qs = repo_version.content.filter(pulp_type='rpm.package')
+                if package_qs.count():
+                    pkg_checksum_type = package_qs.first().cast().checksum_type
+                    checksum_types = {
+                        'metadata': pkg_checksum_type,
+                        'package': pkg_checksum_type
+                    }
             sqlite = pulp2_config.get('generate_sqlite', False)
             try:
                 publish(repo_version.pk, checksum_types=checksum_types, sqlite_metadata=sqlite)