A number of services include the Locations mixin:

https://github.com/googleapis/googleapis/blob/117be9dfdf65ff766a794c8b85d5d7480a1fd83d/google/cloud/location/locations.proto#L29-L32

These mixins do not appear in the .proto file, they only seem to appear in the YAML file:

https://github.com/googleapis/googleapis/blob/117be9dfdf65ff766a794c8b85d5d7480a1fd83d/google/cloud/clouddms/v1/datamigration_v1.yaml#L6-L10

But they are part of the service and included in the API configuration:

https://cloud.google.com/database-migration/docs/reference/rest/v1/projects.locations

https://cloud.google.com/kms/docs/reference/rpc/google.cloud.location

I think the generator needs to support these. It is unclear if these methods should be part of the *Client , or there should be a common google::cloud::LocationClient with suitable endpoint defaults. Or some other solution. The first step is to write some kind of design doc.