I'm importing google.golang.org/api/storagetransfer/v1 in one of my source files and attempting to run mockgen on it results in:

Loading input failed: path/to/source.go:16:24: failed parsing returns: path/to/source.go.go:16:45: unknown package "source"

Adding an alias to the import such as storagetransfer "google.golang.org/api/storagetransfer/v1", appears to resolve it, although Goland complains of a redundant alias.

I am using modules.