From 38abe5b2a4ec5e296a6ab1be569425f8342753a6 Mon Sep 17 00:00:00 2001
From: "Derrick J. Wippler" <thrawn01@gmail.com>
Date: Fri, 30 Jun 2023 14:03:57 -0500
Subject: [PATCH] Added errors.Cause() (#6)

---
 go.mod       |  2 --
 go.sum       |  4 ----
 wrap.go      | 12 ++++++++++++
 wrap_test.go |  9 +++++++++
 4 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/go.mod b/go.mod
index 17301ba..a2b50e3 100644
--- a/go.mod
+++ b/go.mod
@@ -4,14 +4,12 @@ go 1.19
 
 require (
 	github.com/ahmetb/go-linq v3.0.0+incompatible
-	github.com/mailgun/holster/v4 v4.11.0
 	github.com/sirupsen/logrus v1.9.0
 	github.com/stretchr/testify v1.8.1
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
diff --git a/go.sum b/go.sum
index d4ff782..508ca75 100644
--- a/go.sum
+++ b/go.sum
@@ -3,10 +3,6 @@ github.com/ahmetb/go-linq v3.0.0+incompatible/go.mod h1:PFffvbdbtw+QTB0WKRP0cNht
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/mailgun/holster/v4 v4.11.0 h1:c9DT3QZCfiUgcmOYvxJI9rRhLbtX6IqfaClrMjLxkLE=
-github.com/mailgun/holster/v4 v4.11.0/go.mod h1:sXpF+rzEqA89uBEiX19FrVUdbCUKDfR4GRdXmIkINQQ=
-github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
-github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
diff --git a/wrap.go b/wrap.go
index 7aa9793..21c678a 100644
--- a/wrap.go
+++ b/wrap.go
@@ -1,6 +1,7 @@
 package errors
 
 import (
+	"errors"
 	"fmt"
 	"io"
 
@@ -31,6 +32,17 @@ func Wrapf(err error, format string, a ...any) error {
 	}
 }
 
+// Cause returns the last error in the stack of wrapped errors.
+func Cause(err error) error {
+	for {
+		wrapped := errors.Unwrap(err)
+		if wrapped == nil {
+			return err
+		}
+		err = wrapped
+	}
+}
+
 type wrappedError struct {
 	msg     string
 	wrapped error
diff --git a/wrap_test.go b/wrap_test.go
index 77653eb..206f5d0 100644
--- a/wrap_test.go
+++ b/wrap_test.go
@@ -124,3 +124,12 @@ func TestWrapErrorValue(t *testing.T) {
 	wrap := errors.Wrap(err, "message")
 	assert.True(t, errors.Is(wrap, io.EOF))
 }
+
+func TestCause(t *testing.T) {
+	err := errors.Errorf("error: %w", errors.Wrap(errors.Wrap(errors.New("the cause"), "wrap 2"), "wrap 1"))
+	cause := errors.Cause(err)
+	require.Error(t, err)
+	require.Error(t, cause)
+	assert.Equal(t, "error: wrap 1: wrap 2: the cause", err.Error())
+	assert.Equal(t, "the cause", cause.Error())
+}