The Go 2 error values proposal adds functionality to the errors and fmt packages of the standard library for Go 1.13. There is also a compatibility package, golang.org/x/xerrors, for earlier Go versions.

We suggest using the xerrors package for backwards compatibility. When you no longer wish to support Go versions before 1.13, use the corresponding standard library functions.

You need to be prepared that errors you get may be wrapped.

• If you currently compare errors using ==, use xerrors.Is instead. Example:

  if err == io.ErrUnexpectedEOF
  

  becomes

  if xerrors.Is(err, io.ErrUnexpectedEOF)
  

• Checks of the form if err == nil need not be changed.

• Comparisons to io.EOF need not be changed, because io.EOF should never be wrapped.