fix: panic in case NewContext is used to initialize logger with Fatal

entry.go

@@ -90,7 +90,7 @@ func (e ChainEntry) Write() {
 	e.Entry.enc.Release()
 
 	if e.exit {
-		e.Entry.l.ExitFn(1)
+		e.Entry.l.exit(1)
 	}
 }
 

logger.go

@@ -78,6 +78,7 @@ func NewContext(w io.Writer, levels uint8, contextName string) *Logger {
 		w:           w,
 		levels:      levels,
 		contextName: contextName,
+		ExitFn:      os.Exit,
 	}
 }
 
@@ -93,6 +94,7 @@ func (l *Logger) copy(ctxName string) *Logger {
 		w:           l.w,
 		hook:        l.hook,
 		contextName: ctxName,
+		ExitFn:      l.ExitFn,
 	}
 	if len(l.ctx) > 0 {
 		var ctx = make([]func(e Entry), len(l.ctx))
@@ -485,7 +487,7 @@ func (l *Logger) Fatal(msg string) {
 
 	e.enc.Release()
 
-	l.ExitFn(1)
+	l.exit(1)
 }
 
 // FatalWith returns a ChainEntry with FATAL level.
@@ -546,7 +548,7 @@ func (l *Logger) FatalWithFields(msg string, fields func(Entry)) {
 	l.finalizeIfContext(e)
 
 	e.enc.Release()
-	l.ExitFn(1)
+	l.exit(1)
 }
 
 func (l *Logger) openEntry(enc *Encoder) {
@@ -617,6 +619,14 @@ func (l *Logger) closeEntry(e Entry) {
 	}
 }
 
+func (l *Logger) exit(code int) {
+	if l.ExitFn == nil {
+		// fallback to os.Exit to prevent panic incase set as nil.
+		os.Exit(code)
+	}
+	l.ExitFn(code)
+}
+
 // Caller returns the caller in the stack trace, skipped n times.
 func (l *Logger) Caller(n int) string {
 	_, f, fl, _ := runtime.Caller(n)

logger_test.go

@@ -2,6 +2,8 @@ package onelog
 
 import (
 	"errors"
+	"os"
+	"os/exec"
 	"strings"
 	"testing"
 
@@ -80,7 +82,7 @@ func TestOnelogFeature(t *testing.T) {
 		logger := New(nil, DEBUG|INFO|WARN|ERROR|FATAL)
 		str := logger.Caller(1)
 		strs := strings.Split(str, "/")
-		assert.Equal(t, "logger_test.go:81", strs[len(strs)-1], "file should be logger_test.go:81")
+		assert.Equal(t, "logger_test.go:83", strs[len(strs)-1], "file should be logger_test.go:81")
 	})
 }
 func TestOnelogWithoutFields(t *testing.T) {
@@ -1256,3 +1258,25 @@ func TestOnelogFieldsChainAndContext(t *testing.T) {
 		logger.Fatal("message")
 	})
 }
+
+func TestFatalActualOsExit(t *testing.T) {
+	if os.Getenv("FatalActualOsExit") == "1" {
+		parent := NewContext(os.Stdout, DEBUG|INFO|WARN|ERROR|FATAL, "params")
+		logger := parent.WithContext("")
+		logger.ExitFn = nil
+		logger.FatalWithFields("message", func(e Entry) {
+			e.String("userID", "123456")
+			e.String("action", "login")
+			e.String("result", "success")
+			e.Int64("int64", 120)
+		})
+		return
+	}
+	cmd := exec.Command(os.Args[0], "-test.run=TestFatalActualOsExit")
+	cmd.Env = append(os.Environ(), "FatalActualOsExit=1")
+	err := cmd.Run()
+	if e, ok := err.(*exec.ExitError); ok && !e.Success() {
+		return
+	}
+	t.Fatalf("process ran with err %v, want exit status 1", err)
+}