make caller filepath package/file style

this code is from zap
9a9fa7d4b5/zapcore/entry.go (L101)

logger/default.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"os"
-	"path/filepath"
 	"runtime"
 	"sort"
 	"strings"
@@ -55,9 +54,28 @@ func copyFields(src map[string]interface{}) map[string]interface{} {
 	return dst
 }
 
+// logCallerfilePath returns a package/file:line description of the caller,
+// preserving only the leaf directory name and file name.
 func logCallerfilePath(loggingFilePath string) string {
-	parts := strings.Split(loggingFilePath, string(filepath.Separator))
+	// To make sure we trim the path correctly on Windows too, we
-	return parts[len(parts)-1]
+	// counter-intuitively need to use '/' and *not* os.PathSeparator here,
+	// because the path given originates from Go stdlib, specifically
+	// runtime.Caller() which (as of Mar/17) returns forward slashes even on
+	// Windows.
+	//
+	// See https://github.com/golang/go/issues/3335
+	// and https://github.com/golang/go/issues/18151
+	//
+	// for discussion on the issue on Go side.
+	idx := strings.LastIndexByte(loggingFilePath, '/')
+	if idx == -1 {
+		return loggingFilePath
+	}
+	idx = strings.LastIndexByte(loggingFilePath[:idx], '/')
+	if idx == -1 {
+		return loggingFilePath
+	}
+	return loggingFilePath[idx+1:]
 }
 
 func (l *defaultLogger) Log(level Level, v ...interface{}) {