Unwrap in Walk for compat with go1.13 errors

errwrap.go

@@ -44,6 +44,8 @@ func Wrap(outer, inner error) error {
 //
 // format is the format of the error message. The string '{{err}}' will
 // be replaced with the original error message.
+//
+// Deprecated: Use fmt.Errorf()
 func Wrapf(format string, err error) error {
 	outerMsg := "<nil>"
 	if err != nil {
@@ -148,11 +150,15 @@ func Walk(err error, cb WalkFunc) {
 		for _, err := range e.WrappedErrors() {
 			Walk(err, cb)
 		}
+	case interface { Unwrap() error }:
+		cb(err)
+		Walk(e.Unwrap(), cb)
 	default:
 		cb(err)
 	}
 }
 
+
 // wrappedError is an implementation of error that has both the
 // outer and inner errors.
 type wrappedError struct {

errwrap_test.go

@@ -42,6 +42,16 @@ func TestGetAll(t *testing.T) {
 			"foo",
 			1,
 		},
+		{
+			fmt.Errorf("foo: %w", fmt.Errorf("bar")),
+			"foo: bar",
+			1,
+		},
+		{
+			fmt.Errorf("foo: %w", fmt.Errorf("bar")),
+			"bar",
+			1,
+		},
 	}
 
 	for i, tc := range cases {
@@ -84,6 +94,11 @@ func TestGetAllType(t *testing.T) {
 			Wrapf("", nil),
 			0,
 		},
+		{
+			fmt.Errorf("one: %w", fmt.Errorf("two: %w", fmt.Errorf("three"))),
+			fmt.Errorf("%w", errors.New("")),
+			2,
+		},
 	}
 
 	for i, tc := range cases {