generate proto from bigquery schema

[derekperkins]

We're wanting to migrate all our schema interactions to happen proto first, but that's tough because we have lots of BigQuery schemas with no matching proto. It would help us if we could provide the schema json, and use that to create the proto scaffold. In most cases, I think that's a one-time translation, but I think there are also use cases if you don't control a schema, where it would be convenient to keep the proto in sync as the upstream BigQuery schema changes.

[jordanfowler]

@derekperkins Not sure if you've looked into this, but there is a way to get a protoreflect.MessageDescriptor directly from a bigquery schema using the following method:

// adapt from: cloud.google.com/go/bigquery/storage/managedwriter/adapt
var schema bigquery.Schema
tableSchema, err := adapt.BQSchemaToStorageTableSchema(schema)
if err != nil {
	return nil, err
}

schemaDescriptor, err := adapt.StorageSchemaToProto2Descriptor(tableSchema, "root")
if err != nil {
	return nil, err
}

messageDescriptor, ok := schemaDescriptor.(protoreflect.MessageDescriptor)
if !ok {
	return nil, fmt.Errorf("schema descriptor is not a message descriptor")
}

[derekperkins]

I haven't checked that out, thanks for the suggestion!