bugprone-unused-raii

Finds temporaries that look like RAII objects.

The canonical example for this is a scoped lock.

{
  scoped_lock(&global_mutex);
  critical_section();
}

The destructor of the scoped_lock is called before the critical_section is entered, leaving it unprotected.

We apply a number of heuristics to reduce the false positive count of this check:

• Ignore code expanded from macros. Testing frameworks make heavy use of this.
• Ignore types with trivial destructors. They are very unlikely to be RAII objects and there's no difference when they are deleted.
• Ignore objects at the end of a compound statement (doesn't change behavior).
• Ignore objects returned from a call.