! go get -d example.com/retract/ambiguous/other
stderr 'ambiguous import: found package example.com/retract/ambiguous/nested in multiple modules:'
stderr '^go: warning: example.com/retract/ambiguous/nested@v1.9.0-bad: retracted by module author: nested modules are bad$'

-- go.mod --
module example.com/use

go 1.16

require example.com/retract/ambiguous/nested v1.9.0-bad