Fix go1.19

.travis.yml

@@ -2,7 +2,6 @@ language: go
 
 go:
   - "1.8.x"
-  - "1.10.x"
-  - "1.13.x"
-  - "1.14.x"
+  - "1.11.x"
   - "1.16.x"
+  - "1.21.x"

error_1_13.go

@@ -33,29 +33,3 @@ func Is(e error, original error) bool {
 
 	return false
 }
-
-// Join returns an error that wraps the given errors.
-// Any nil error values are discarded.
-// Join returns nil if every value in errs is nil.
-// The error formats as the concatenation of the strings obtained
-// by calling the Error method of each element of errs, with a newline
-// between each string.
-//
-// A non-nil error returned by Join implements the Unwrap() []error method.
-//
-// For more information see stdlib errors.Join.
-func Join(errs ...error) error {
-	return baseErrors.Join(errs...)
-}
-
-// Unwrap returns the result of calling the Unwrap method on err, if err's
-// type contains an Unwrap method returning error.
-// Otherwise, Unwrap returns nil.
-//
-// Unwrap only calls a method of the form "Unwrap() error".
-// In particular Unwrap does not unwrap errors returned by [Join].
-//
-// For more information see stdlib errors.Unwrap.
-func Unwrap(err error) error {
-	return baseErrors.Unwrap(err)
-}

join_unwrap_1_20.go

@@ -0,0 +1,32 @@
+//go:build go1.20
+// +build go1.20
+
+package errors
+
+import baseErrors "errors"
+
+// Join returns an error that wraps the given errors.
+// Any nil error values are discarded.
+// Join returns nil if every value in errs is nil.
+// The error formats as the concatenation of the strings obtained
+// by calling the Error method of each element of errs, with a newline
+// between each string.
+//
+// A non-nil error returned by Join implements the Unwrap() []error method.
+//
+// For more information see stdlib errors.Join.
+func Join(errs ...error) error {
+	return baseErrors.Join(errs...)
+}
+
+// Unwrap returns the result of calling the Unwrap method on err, if err's
+// type contains an Unwrap method returning error.
+// Otherwise, Unwrap returns nil.
+//
+// Unwrap only calls a method of the form "Unwrap() error".
+// In particular Unwrap does not unwrap errors returned by [Join].
+//
+// For more information see stdlib errors.Unwrap.
+func Unwrap(err error) error {
+	return baseErrors.Unwrap(err)
+}

join_unwrap_backward.go

@@ -0,0 +1,71 @@
+//go:build !go1.20
+// +build !go1.20
+
+package errors
+
+// Disclaimer: functions Join and Unwrap are copied from the stdlib errors
+// package v1.21.0.
+
+// Join returns an error that wraps the given errors.
+// Any nil error values are discarded.
+// Join returns nil if every value in errs is nil.
+// The error formats as the concatenation of the strings obtained
+// by calling the Error method of each element of errs, with a newline
+// between each string.
+//
+// A non-nil error returned by Join implements the Unwrap() []error method.
+func Join(errs ...error) error {
+	n := 0
+	for _, err := range errs {
+		if err != nil {
+			n++
+		}
+	}
+	if n == 0 {
+		return nil
+	}
+	e := &joinError{
+		errs: make([]error, 0, n),
+	}
+	for _, err := range errs {
+		if err != nil {
+			e.errs = append(e.errs, err)
+		}
+	}
+	return e
+}
+
+type joinError struct {
+	errs []error
+}
+
+func (e *joinError) Error() string {
+	var b []byte
+	for i, err := range e.errs {
+		if i > 0 {
+			b = append(b, '\n')
+		}
+		b = append(b, err.Error()...)
+	}
+	return string(b)
+}
+
+func (e *joinError) Unwrap() []error {
+	return e.errs
+}
+
+// Unwrap returns the result of calling the Unwrap method on err, if err's
+// type contains an Unwrap method returning error.
+// Otherwise, Unwrap returns nil.
+//
+// Unwrap only calls a method of the form "Unwrap() error".
+// In particular Unwrap does not unwrap errors returned by [Join].
+func Unwrap(err error) error {
+	u, ok := err.(interface {
+		Unwrap() error
+	})
+	if !ok {
+		return nil
+	}
+	return u.Unwrap()
+}