import (
"errors"
"fmt"
)
// *** before: ***
func readConfig() error {
err := errors.New("file not found")
return fmt.Errorf("read config: %v", err)
}
// the original error is lost, nothing further down can compare with it
// *** in version 1.13: ***
var ErrNotFound = errors.New("file not found")
func readConfig() error {
return fmt.Errorf("read config: %w", ErrNotFound)
}