-- go.mod --
module example.com
go 1.18

-- template/template.go --
package template

import (
	"errors"
	"fmt"
)

func before(s string) error { return fmt.Errorf("%s", s) }
func after(s string) error {
	n := fmt.Sprintf("error - %s", s)
	return errors.New(n)
}

-- in/i1/i1.go --
package i1

import "fmt"

func example() {
	_ = fmt.Errorf("%s", "foo")
}

-- out/i1/i1.go --
package i1

import (
	"errors"
	"fmt"
)

func example() {

	n := fmt.Sprintf("error - %s", "foo")
	_ = errors.New(n)
}