From cd0f0abbb8169eea406e2eabea2d4efc8deed126 Mon Sep 17 00:00:00 2001
From: tdakkota <tanc13@yandex.ru>
Date: Mon, 21 Feb 2022 17:10:38 +0300
Subject: [PATCH] feat: add Cause function

---
 cause_test.go | 22 ++++++++++++++++++++++
 frame.go      |  6 +++---
 wrap.go       | 14 ++++++++++++++
 3 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 cause_test.go

diff --git a/cause_test.go b/cause_test.go
new file mode 100644
index 0000000..641baf5
--- /dev/null
+++ b/cause_test.go
@@ -0,0 +1,22 @@
+package errors
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+func TestCause(t *testing.T) {
+	err1 := fmt.Errorf("1")
+	erra := Wrap(err1, "wrap 2")
+	errb := Wrap(erra, "wrap3")
+
+	v, ok := Cause(errb)
+	if !ok {
+		t.Error("unexpected false")
+		return
+	}
+	if !reflect.DeepEqual(v, erra.(*wrapError).frame) {
+		t.Errorf("want %+v, got %+v", v, erra.(*wrapError).frame)
+	}
+}
diff --git a/frame.go b/frame.go
index 75ec0df..e74908c 100644
--- a/frame.go
+++ b/frame.go
@@ -25,10 +25,10 @@ func Caller(skip int) Frame {
 	return s
 }
 
-// location reports the file, line, and function of a frame.
+// Location reports the file, line, and function of a frame.
 //
 // The returned function may be "" even if file and line are not.
-func (f Frame) location() (function, file string, line int) {
+func (f Frame) Location() (function, file string, line int) {
 	frames := runtime.CallersFrames(f.frames[:])
 	if _, ok := frames.Next(); !ok {
 		return "", "", 0
@@ -45,7 +45,7 @@ func (f Frame) location() (function, file string, line int) {
 // after printing any other error detail.
 func (f Frame) Format(p Printer) {
 	if p.Detail() {
-		function, file, line := f.location()
+		function, file, line := f.Location()
 		if function != "" {
 			p.Printf("%s\n    ", function)
 		}
diff --git a/wrap.go b/wrap.go
index 7833483..61f008f 100644
--- a/wrap.go
+++ b/wrap.go
@@ -41,6 +41,20 @@ func Unwrap(err error) error {
 	return errors.Unwrap(err)
 }
 
+// Cause returns first recorded Frame.
+func Cause(err error) (f Frame, r bool) {
+	for {
+		we, ok := err.(*wrapError)
+		if !ok {
+			return f, r
+		}
+		f = we.frame
+		r = r || ok
+
+		err = we.err
+	}
+}
+
 type wrapError struct {
 	msg   string
 	err   error