Incompatible with Google Cloud SQL proxy socket connections

Google recommends using Google Cloud SQL proxy, which creates a local UNIX socket, to connect to its managed SQL service. These sockets are generated in the format:

project:region:instance

So you end up with a local file like:

/run/cloud_sql_proxy/my-project:us-central1:my-instance

Using this local file in db-config.php like:

'host' => 'localhost:/run/cloud_sql_proxy/my-project:us-central1:my-instance

Generates thousands of global__r errors in the debug.log and basically breaks everything. I think the colons in the local file aren’t being escaped / interpreted correctly and that makes the database unreachable.