Panic In Defer (ARCH5155)

Key go.logging.panic-in-defer · Severity error · Category logging

Panicking inside a defer block masks any in-flight error from the function body. This is the Go analogue of throwing from a finally block.

Incorrect

func process(path string) error {
  f, err := os.Open(path)
  if err != nil {
    return err
  }
  defer func() {
    if err := f.Close(); err != nil {
      panic(err) // masks the real error
    }
  }()
  return parse(f)
}

Correct

func process(path string) (err error) {
  f, err := os.Open(path)
  if err != nil {
    return err
  }
  defer func() {
    if cerr := f.Close(); cerr != nil && err == nil {
      err = cerr
    }
  }()
  return parse(f)
}

Fix

Assign the error to a named return value instead of panicking in defer, and don’t overwrite an existing error.