From eb18a1a6b819f87b37f0a886506f0943c71d1456 Mon Sep 17 00:00:00 2001
From: izumin5210 <m@izum.in>
Date: Fri, 22 Nov 2019 23:28:02 +0900
Subject: [PATCH 1/2] Check error comparability for avoiding panic

---
 pkgerrors.go      | 12 ++++++++++--
 pkgerrors_test.go | 28 ++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/pkgerrors.go b/pkgerrors.go
index 785a12b..44a8cba 100644
--- a/pkgerrors.go
+++ b/pkgerrors.go
@@ -1,6 +1,7 @@
 package fail
 
 import (
+	"reflect"
 	"strings"
 
 	pkgerrors "github.com/pkg/errors"
@@ -79,8 +80,15 @@ func extractPkgError(err error) *pkgError {
 		break
 	}
 
-	if len(stackTraces) == 0 && rootErr == err {
-		return nil
+	if len(stackTraces) == 0 {
+		ret, et := reflect.TypeOf(rootErr), reflect.TypeOf(err)
+		if ret != nil && et != nil && ret.Comparable() && et.Comparable() {
+			if rootErr == err {
+				return nil
+			}
+		} else if reflect.DeepEqual(rootErr, err) {
+			return nil
+		}
 	}
 
 	// Extract annotated messages by removing the trailing message.
diff --git a/pkgerrors_test.go b/pkgerrors_test.go
index 41d41ce..e9dda20 100644
--- a/pkgerrors_test.go
+++ b/pkgerrors_test.go
@@ -2,6 +2,7 @@ package fail
 
 import (
 	"errors"
+	"strings"
 	"testing"
 
 	pkgerrors "github.com/pkg/errors"
@@ -20,6 +21,13 @@ func TestExtractPkgError(t *testing.T) {
 		assert.Nil(t, pkgErr)
 	})
 
+	t.Run("slice error", func(t *testing.T) {
+		err := errorSlice{errors.New("error")}
+
+		pkgErr := extractPkgError(err)
+		assert.Nil(t, pkgErr)
+	})
+
 	t.Run("pkg/errors.New", func(t *testing.T) {
 		err := pkgErrorsNew("message")
 
@@ -84,6 +92,16 @@ func TestExtractPkgError(t *testing.T) {
 			assert.NotEmpty(t, pkgErr.StackTrace)
 			assert.Equal(t, "pkgErrorsWrap", pkgErr.StackTrace[0].Func)
 		})
+
+		t.Run("with slice error", func(t *testing.T) {
+			err0 := errorSlice{errors.New("error")}
+			err1 := pkgErrorsWrap(err0, "message")
+
+			pkgErr := extractPkgError(err1)
+			assert.NotNil(t, pkgErr)
+			assert.Equal(t, err0, pkgErr.Err)
+			assert.NotEmpty(t, pkgErr.StackTrace)
+		})
 	})
 
 	t.Run("pkg/errors.WithMessage", func(t *testing.T) {
@@ -156,3 +174,13 @@ func pkgErrorsNew(msg string) error {
 func pkgErrorsWrap(err error, msg string) error {
 	return pkgerrors.Wrap(err, msg)
 }
+
+type errorSlice []error
+
+func (s errorSlice) Error() string {
+	msg := make([]string, len(s))
+	for i, e := range s {
+		msg[i] = e.Error()
+	}
+	return strings.Join(msg, ": ")
+}

From 4dc2444760cf27e435c692cb158ffd17ba314a84 Mon Sep 17 00:00:00 2001
From: Yuki Iwanaga <yuki@creasty.com>
Date: Tue, 14 Jan 2020 14:05:25 +0900
Subject: [PATCH 2/2] Remove redundant comparison

---
 pkgerrors.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkgerrors.go b/pkgerrors.go
index 44a8cba..bd1624e 100644
--- a/pkgerrors.go
+++ b/pkgerrors.go
@@ -86,7 +86,7 @@ func extractPkgError(err error) *pkgError {
 			if rootErr == err {
 				return nil
 			}
-		} else if reflect.DeepEqual(rootErr, err) {
+		} else {
 			return nil
 		}
 	}