Re-vendor

vendor/github.com/pkg/errors/errors.go

@@ -82,7 +82,7 @@
 //
 //     if err, ok := err.(stackTracer); ok {
 //             for _, f := range err.StackTrace() {
-//                     fmt.Printf("%+s:%d\n", f, f)
+//                     fmt.Printf("%+s:%d", f)
 //             }
 //     }
 //
@@ -159,9 +159,6 @@ type withStack struct {
 
 func (w *withStack) Cause() error { return w.error }
 
-// Unwrap provides compatibility for Go 1.13 error chains.
-func (w *withStack) Unwrap() error { return w.error }
-
 func (w *withStack) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
@@ -244,9 +241,6 @@ type withMessage struct {
 func (w *withMessage) Error() string { return w.msg + ": " + w.cause.Error() }
 func (w *withMessage) Cause() error  { return w.cause }
 
-// Unwrap provides compatibility for Go 1.13 error chains.
-func (w *withMessage) Unwrap() error { return w.cause }
-
 func (w *withMessage) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
@@ -260,3 +254,29 @@ func (w *withMessage) Format(s fmt.State, verb rune) {
 		io.WriteString(s, w.Error())
 	}
 }
+
+// Cause returns the underlying cause of the error, if possible.
+// An error value has a cause if it implements the following
+// interface:
+//
+//     type causer interface {
+//            Cause() error
+//     }
+//
+// If the error does not implement Cause, the original error will
+// be returned. If the error is nil, nil will be returned without further
+// investigation.
+func Cause(err error) error {
+	type causer interface {
+		Cause() error
+	}
+
+	for err != nil {
+		cause, ok := err.(causer)
+		if !ok {
+			break
+		}
+		err = cause.Cause()
+	}
+	return err
+}