From e490247d3b5bc48f82fdd9a1a357a2455106e6f2 Mon Sep 17 00:00:00 2001
From: Tobias Klauser <tklauser@distanz.ch>
Date: Fri, 5 Feb 2021 00:27:06 +0100
Subject: [PATCH] =?UTF-8?q?cmp/cmpopts:=20use=20errors.Is=20with=20?=
 =?UTF-8?q?=E2=89=A5go1.13=20in=20compareErrors?=
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Use the standard definition of errors.Is to implement compareErrors with
≥go1.13. Retain the implementation using golang.org/x/xerrors for versions <go1.13.

This will allow packages using newer Go versions and already relying on
the errors package to get rid of the transitive dependency on
golang.org/x/xerrors.
---
 cmp/cmpopts/equate.go         |  8 --------
 cmp/cmpopts/errors_go113.go   | 15 +++++++++++++++
 cmp/cmpopts/errors_xerrors.go | 18 ++++++++++++++++++
 3 files changed, 33 insertions(+), 8 deletions(-)
 create mode 100644 cmp/cmpopts/errors_go113.go
 create mode 100644 cmp/cmpopts/errors_xerrors.go

diff --git a/cmp/cmpopts/equate.go b/cmp/cmpopts/equate.go
index 51ce36f..e4ffca8 100644
--- a/cmp/cmpopts/equate.go
+++ b/cmp/cmpopts/equate.go
@@ -11,7 +11,6 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"golang.org/x/xerrors"
 )
 
 func equateAlways(_, _ interface{}) bool { return true }
@@ -147,10 +146,3 @@ func areConcreteErrors(x, y interface{}) bool {
 	_, ok2 := y.(error)
 	return ok1 && ok2
 }
-
-func compareErrors(x, y interface{}) bool {
-	xe := x.(error)
-	ye := y.(error)
-	// TODO(≥go1.13): Use standard definition of errors.Is.
-	return xerrors.Is(xe, ye) || xerrors.Is(ye, xe)
-}
diff --git a/cmp/cmpopts/errors_go113.go b/cmp/cmpopts/errors_go113.go
new file mode 100644
index 0000000..26fe25d
--- /dev/null
+++ b/cmp/cmpopts/errors_go113.go
@@ -0,0 +1,15 @@
+// Copyright 2021, 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 cmpopts
+
+import "errors"
+
+func compareErrors(x, y interface{}) bool {
+	xe := x.(error)
+	ye := y.(error)
+	return errors.Is(xe, ye) || errors.Is(ye, xe)
+}
diff --git a/cmp/cmpopts/errors_xerrors.go b/cmp/cmpopts/errors_xerrors.go
new file mode 100644
index 0000000..6eeb8d6
--- /dev/null
+++ b/cmp/cmpopts/errors_xerrors.go
@@ -0,0 +1,18 @@
+// Copyright 2021, 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
+
+// TODO(≥go1.13): For support on <go1.13, we use the xerrors package.
+// Drop this file when we no longer support older Go versions.
+
+package cmpopts
+
+import "golang.org/x/xerrors"
+
+func compareErrors(x, y interface{}) bool {
+	xe := x.(error)
+	ye := y.(error)
+	return xerrors.Is(xe, ye) || xerrors.Is(ye, xe)
+}