Tests of reference to implicit type switch vars, which are
a special case in go/types.Info{Def,Use,Implicits}.

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

-- a/a.go --
package a

func _(x interface{}) {
	switch y := x.(type) { //@loc(yDecl, "y"), refs("y", yDecl, yInt, yDefault)
	case int:
		println(y) //@loc(yInt, "y"), refs("y", yDecl, yInt, yDefault)
	default:
		println(y) //@loc(yDefault, "y")
	}
}