in encoder.go [111:123]
func (c *caller) MarshalLogObject(enc zapcore.ObjectEncoder) error {
var file string
if c.fullPath {
file = c.File
} else {
file = c.TrimmedPath()
file = file[:strings.LastIndex(file, ":")]
}
enc.AddString("function", c.Function)
enc.AddString("file.name", file)
enc.AddInt("file.line", c.Line)
return nil
}