Accidentally copying a value containing a lock may cause both copies to work incorrectly. Generally, such values should be referred to through a pointer. A lock here means a type implementing sync.Locker, such as sync.Mutex or sync.WaitGroup.

Example:

type SafeInt struct {
  m sync.Mutex
  i int
}

func (s SafeInt) Inc() { // mutex is copied
  s.m.Lock()
  s.i++
  s.m.Unlock()
}

After the Add pointer quick-fix is applied:

type SafeInt struct {
  m sync.Mutex
  i int
}

func (s *SafeInt) Inc() {
  s.m.Lock()
  s.i++
  s.m.Unlock()
}