Add the ability to capture the logger caller file and line number

Fixes #34, #22

context.go

@@ -302,3 +302,17 @@ func (c Context) Interface(key string, i interface{}) Context {
 	c.l.context = json.AppendInterface(json.AppendKey(c.l.context, key), i)
 	return c
 }
+
+type callerHook struct{}
+
+func (ch callerHook) Run(e *Event, level Level, msg string) {
+	e.caller(4)
+}
+
+var ch = callerHook{}
+
+// Caller adds the file:line of the caller with the zerolog.CallerFieldName key.
+func (c Context) Caller() Context {
+	c.l = c.l.Hook(ch)
+	return c
+}

event.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"runtime"
+	"strconv"
 	"sync"
 	"time"
 
@@ -561,3 +563,20 @@ func (e *Event) Interface(key string, i interface{}) *Event {
 	e.buf = json.AppendInterface(json.AppendKey(e.buf, key), i)
 	return e
 }
+
+// Caller adds the file:line of the caller with the zerolog.CallerFieldName key.
+func (e *Event) Caller() *Event {
+	return e.caller(2)
+}
+
+func (e *Event) caller(skip int) *Event {
+	if e == nil {
+		return e
+	}
+	_, file, line, ok := runtime.Caller(skip)
+	if !ok {
+		return e
+	}
+	e.buf = json.AppendString(json.AppendKey(e.buf, CallerFieldName), file+":"+strconv.Itoa(line))
+	return e
+}

globals.go

@@ -16,6 +16,9 @@ var (
 	// ErrorFieldName is the field name used for error fields.
 	ErrorFieldName = "error"
 
+	// CallerFieldName is the field name used for caller field.
+	CallerFieldName = "caller"
+
 	// TimeFieldFormat defines the time format of the Time field type.
 	// If set to an empty string, the time is formatted as an UNIX timestamp
 	// as integer.

log_test.go

@@ -3,7 +3,9 @@ package zerolog
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"reflect"
+	"runtime"
 	"testing"
 	"time"
 )
@@ -74,7 +76,7 @@ func TestInfo(t *testing.T) {
 
 func TestWith(t *testing.T) {
 	out := &bytes.Buffer{}
-	log := New(out).With().
+	ctx := New(out).With().
 		Str("foo", "bar").
 		AnErr("some_err", nil).
 		Err(errors.New("some error")).
@@ -91,10 +93,12 @@ func TestWith(t *testing.T) {
 		Uint64("uint64", 10).
 		Float32("float32", 11).
 		Float64("float64", 12).
-		Time("time", time.Time{}).
+		Time("time", time.Time{})
-		Logger()
+	_, file, line, _ := runtime.Caller(0)
+	caller := fmt.Sprintf("%s:%d", file, line+3)
+	log := ctx.Caller().Logger()
 	log.Log().Msg("")
-	if got, want := out.String(), `{"foo":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"time":"0001-01-01T00:00:00Z"}`+"\n"; got != want {
+	if got, want := out.String(), `{"foo":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"time":"0001-01-01T00:00:00Z","caller":"`+caller+`"}`+"\n"; got != want {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
 }
@@ -132,7 +136,10 @@ func TestFields(t *testing.T) {
 	out := &bytes.Buffer{}
 	log := New(out)
 	now := time.Now()
+	_, file, line, _ := runtime.Caller(0)
+	caller := fmt.Sprintf("%s:%d", file, line+3)
 	log.Log().
+		Caller().
 		Str("string", "foo").
 		Bytes("bytes", []byte("bar")).
 		AnErr("some_err", nil).
@@ -154,7 +161,7 @@ func TestFields(t *testing.T) {
 		Time("time", time.Time{}).
 		TimeDiff("diff", now, now.Add(-10*time.Second)).
 		Msg("")
-	if got, want := out.String(), `{"string":"foo","bytes":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"dur":1000,"time":"0001-01-01T00:00:00Z","diff":10000}`+"\n"; got != want {
+	if got, want := out.String(), `{"caller":"`+caller+`","string":"foo","bytes":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"dur":1000,"time":"0001-01-01T00:00:00Z","diff":10000}`+"\n"; got != want {
 		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
 	}
 }