Fix error chain from pkgerrors (#552)

pkgerrors/stacktrace.go

@@ -47,10 +47,27 @@ func MarshalStack(err error) interface{} {
 	type stackTracer interface {
 		StackTrace() errors.StackTrace
 	}
-	sterr, ok := err.(stackTracer)
+	var sterr stackTracer
+	var ok bool
+	for err != nil {
+		sterr, ok = err.(stackTracer)
+		if ok {
+			break
+		}
+
+		u, ok := err.(interface {
+			Unwrap() error
+		})
 		if !ok {
 			return nil
 		}
+
+		err = u.Unwrap()
+	}
+	if sterr == nil {
+		return nil
+	}
+
 	st := sterr.StackTrace()
 	s := &state{}
 	out := make([]map[string]string, 0, len(st))

pkgerrors/stacktrace_test.go

@@ -4,6 +4,7 @@ package pkgerrors
 
 import (
 	"bytes"
+	"fmt"
 	"regexp"
 	"testing"
 
@@ -17,11 +18,11 @@ func TestLogStack(t *testing.T) {
 	out := &bytes.Buffer{}
 	log := zerolog.New(out)
 
-	err := errors.Wrap(errors.New("error message"), "from error")
+	err := fmt.Errorf("from error: %w", errors.New("error message"))
 	log.Log().Stack().Err(err).Msg("")
 
 	got := out.String()
-	want := `\{"stack":\[\{"func":"TestLogStack","line":"20","source":"stacktrace_test.go"\},.*\],"error":"from error: error message"\}\n`
+	want := `\{"stack":\[\{"func":"TestLogStack","line":"21","source":"stacktrace_test.go"\},.*\],"error":"from error: error message"\}\n`
 	if ok, _ := regexp.MatchString(want, got); !ok {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
@@ -33,11 +34,11 @@ func TestLogStackFromContext(t *testing.T) {
 	out := &bytes.Buffer{}
 	log := zerolog.New(out).With().Stack().Logger() // calling Stack() on log context instead of event
 
-	err := errors.Wrap(errors.New("error message"), "from error")
+	err := fmt.Errorf("from error: %w", errors.New("error message"))
 	log.Log().Err(err).Msg("") // not explicitly calling Stack()
 
 	got := out.String()
-	want := `\{"stack":\[\{"func":"TestLogStackFromContext","line":"36","source":"stacktrace_test.go"\},.*\],"error":"from error: error message"\}\n`
+	want := `\{"stack":\[\{"func":"TestLogStackFromContext","line":"37","source":"stacktrace_test.go"\},.*\],"error":"from error: error message"\}\n`
 	if ok, _ := regexp.MatchString(want, got); !ok {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}