env GO111MODULE=off

! go build canonical/d
stderr 'package canonical/d'
stderr 'imports canonical/b'
stderr 'imports canonical/a/: non-canonical'

-- canonical/a/a.go --
package a

import _ "c"
-- canonical/b/b.go --
package b

import _ "canonical/a/"
-- canonical/a/vendor/c/c.go --
package c
-- canonical/d/d.go --
package d

import _ "canonical/b"