fix func Cause(error) error returning nil on the root cause error

[win-t]

Some error struct have Cause() error method indicating the cause of
the error, but that method could return nil indicating that that itself
is the root cause in the error chain

look at this struct

type myError struct {
  message string
  cause   error
}

func (m *myError) Error() string { ... }

func (m *myError) Cause() error {
  return m.cause
}

func New(message string) error {
  return &myError{message: message}
}

[davecheney]

Can you please add a test so this change is not accidentally reverted in the future. Thank you.

…

On 15 Jan 2020, at 19:16, Kurnia D Win ***@***.***> wrote:  Some error struct have Cause() error method indicating the cause of the error, but that method could return nil indicating that that itself is the root cause in the error chain look at this struct type myError struct { message string cause error } func (m *myError) Error() string { ... } func (m *myError) Cause() error { return m.cause } func New(message string) error { return &myError{message: message} } You can view, comment on, or merge this pull request online at: #221 Commit Summary fix Cause File Changes M errors.go (6) Patch Links: https://github.com/pkg/errors/pull/221.patch https://github.com/pkg/errors/pull/221.diff — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[puellanivis]

We can avoid the spurious break control flow by structuring this the other way around:

cerr := cause.Cause()
if cerr == nil {
	return err
}
err = cerr

[puellanivis]

Also, this is a duplicate of #143