pkgerrors: remove fmt dep

pkgerrors/stacktrace.go

@@ -1,8 +1,6 @@
 package pkgerrors
 
 import (
-	"fmt"
-
 	"github.com/pkg/errors"
 )
 
@@ -12,6 +10,36 @@ var (
 	StackSourceFunctionName = "func"
 )
 
+type state struct {
+	b []byte
+}
+
+// Write implement fmt.Formatter interface.
+func (s *state) Write(b []byte) (n int, err error) {
+	s.b = b
+	return len(b), nil
+}
+
+// Width implement fmt.Formatter interface.
+func (s *state) Width() (wid int, ok bool) {
+	return 0, false
+}
+
+// Precision implement fmt.Formatter interface.
+func (s *state) Precision() (prec int, ok bool) {
+	return 0, false
+}
+
+// Flag implement fmt.Formatter interface.
+func (s *state) Flag(c int) bool {
+	return false
+}
+
+func frameField(f errors.Frame, s *state, c rune) string {
+	f.Format(s, c)
+	return string(s.b)
+}
+
 // MarshalStack implements pkg/errors stack trace marshaling.
 //
 //   zerolog.ErrorStackMarshaler = MarshalStack
@@ -25,12 +53,13 @@ func MarshalStack(err error) interface{} {
 	} else {
 		return nil
 	}
+	s := &state{}
 	out := make([]map[string]string, 0, len(st))
 	for _, frame := range st {
 		out = append(out, map[string]string{
-			StackSourceFileName:     fmt.Sprintf("%s", frame),
-			StackSourceLineName:     fmt.Sprintf("%d", frame),
-			StackSourceFunctionName: fmt.Sprintf("%n", frame),
+			StackSourceFileName:     frameField(frame, s, 's'),
+			StackSourceLineName:     frameField(frame, s, 'd'),
+			StackSourceFunctionName: frameField(frame, s, 'n'),
 		})
 	}
 	return out

pkgerrors/stacktrace_test.go

@@ -26,3 +26,16 @@ func TestLogStack(t *testing.T) {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
 }
+
+func BenchmarkLogStack(b *testing.B) {
+	zerolog.ErrorStackMarshaler = MarshalStack
+	out := &bytes.Buffer{}
+	log := zerolog.New(out)
+	err := errors.Wrap(errors.New("error message"), "from error")
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		log.Log().Stack().Err(err).Msg("")
+		out.Reset()
+	}
+}