undef.go:12:6: error: reference to undefined name ‘x’
undef.go:13:6: error: reference to undefined name ‘x’
undef.go:14:6: error: reference to undefined name ‘x’
undef.go:22:25: error: reference to undefined name ‘y’
undef.go:42:11: error: reference to undefined name ‘v’

R=rsc
CC=golang-dev
https://golang.org/cl/2152045