proto, internal/errors: add Error sentinel, errors.Wrap
Add a sentinel proto.Error error which matches all errors returned by
packages in this module.
Document that protoregistry.NotFound is an exact sentinel value for
performance reasons.
Add a Wrap function to the internal/errors package and use it to wrap
errors from outside sources (resolvers). Wrapped errors match
proto.Error.
Fixes golang/protobuf#1021.
Change-Id: I45567df3fd6c8dc9a5caafdb55654827f6fb1941
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/215338
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/internal/errors/is_go112.go b/internal/errors/is_go112.go
new file mode 100644
index 0000000..0f5e585
--- /dev/null
+++ b/internal/errors/is_go112.go
@@ -0,0 +1,42 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !go1.13
+
+package errors
+
+import "reflect"
+
+// Is is a copy of Go 1.13's errors.Is for use with older Go versions.
+func Is(err, target error) bool {
+ if target == nil {
+ return err == target
+ }
+
+ isComparable := reflect.TypeOf(target).Comparable()
+ for {
+ if isComparable && err == target {
+ return true
+ }
+ if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
+ return true
+ }
+ // TODO: consider supporing target.Is(err). This would allow
+ // user-definable predicates, but also may allow for coping with sloppy
+ // APIs, thereby making it easier to get away with them.
+ if err = unwrap(err); err == nil {
+ return false
+ }
+ }
+}
+
+func unwrap(err error) error {
+ u, ok := err.(interface {
+ Unwrap() error
+ })
+ if !ok {
+ return nil
+ }
+ return u.Unwrap()
+}