objc-nsinvocation-argument-lifetime

Finds calls to NSInvocation methods under ARC that don't have proper argument object lifetimes. When passing Objective-C objects as parameters to the NSInvocation methods getArgument:atIndex: and getReturnValue:, the values are copied by value into the argument pointer, which leads to to incorrect releasing behavior if the object pointers are not declared __unsafe_unretained.

For code:

id arg;
[invocation getArgument:&arg atIndex:2];

__strong id returnValue;
[invocation getReturnValue:&returnValue];

The fix will be:

__unsafe_unretained id arg;
[invocation getArgument:&arg atIndex:2];

__unsafe_unretained id returnValue;
[invocation getReturnValue:&returnValue];

The check will warn on being passed instance variable references that have lifetimes other than __unsafe_unretained, but does not propose a fix:

// "id _returnValue" is declaration of instance variable of class.
[invocation getReturnValue:&self->_returnValue];