This test attempts to rename a.S.X to x, which would make it
inaccessible from its external test package. The rename tool
should report an error rather than wrecking the program.
See issue #59403.

-- go.mod --
module example.com
go 1.12

-- a/a.go --
package a

var S struct{ X int } //@renameerr("X", "x", oops)

-- a/a_test.go --
package a_test

import "example.com/a"

var Y = a.S.X

-- @oops --
a/a.go:3:15: renaming "X" to "x" would make it unexported
a/a_test.go:5:13:	breaking references from packages such as "example.com/a_test"