Make "self" cause a compilation error only within blocks.

gistfile1.m

#define self \
	( \
		_Pragma("clang diagnostic push") _Pragma("clang diagnostic ignored \"-Wunused-value\"") self, \
		/* Depends on _cmd being a const copy, like other captured variables. */ \
		_Pragma("clang diagnostic pop") (*(_cmd = _cmd, &self)) \
	)

// Replace libextobjc's @weakify with one that's aware of the "self" macro.
#undef ext_weakify_
#define ext_weakify_(INDEX, CONTEXT, VAR) \
	CONTEXT metamacro_if_eq(metamacro_argcount(VAR), metamacro_argcount(, VAR))(ext_weakify__(VAR))(ext_weakify_self)

#define ext_weakify__(VAR) \
	__typeof__(VAR) metamacro_concat(VAR, _weak_) = (VAR);

#define ext_weakify_self \
	ext_weakify__(metamacro_head self) \
	/* The diagnostic pop from above got stripped out, so we add it back in manually. */ \
	_Pragma("clang diagnostic pop") \
	SEL _cmd_copy = _cmd;

// Replace libextobjc's @strongify with one that's aware of the "self" macro.
#undef ext_strongify_
#define ext_strongify_(INDEX, VAR) \
	metamacro_if_eq(metamacro_argcount(VAR), metamacro_argcount(, VAR))(ext_strongify__(VAR))(ext_strongify_self)

#define ext_strongify__(VAR) \
    __strong __typeof__(VAR) VAR = metamacro_concat(VAR, _weak_);

#define ext_strongify_self \
	ext_strongify__(metamacro_head self) \
	/* The diagnostic pop from above got stripped out, so we add it back in manually. */ \
	_Pragma("clang diagnostic pop") \
	/* Replace _cmd with a mutable variable so that the "self" macro works fine in the block. */ \
	SEL _cmd = _cmd_copy;