In Go 1.16, the go command prints error messages containing suggested commands to fix missing imports.

$ go list example.com/missing
no required module provides package example.com/missing; try 'go get -d example.com/missing' to add it

We should remove the -d flag from these messages. The -d flag is not essential to the operation, its meaning is not obvious to many people, and we're planning to deprecate it and make it a no-op in a future release.