I just found a stupid bug in some of my code where I wrote Var importantValue; NS_ABORT_IF_FALSE(!GetImportValue(&importantValue)); It'd be cool if I could get a warning when I do stupid things like this. There are a couple of complications: (1) Definition of "side-effecty." Some debug checks, like NS_ASSERT(!!ptr), end up making method calls to smart pointers, which look side-effecty but should be ignored. These would probably need to be special-cased. (2) SanityCheck()-type methods, e.g. NS_ASSERT(SanityCheck()). Personally I prefer a conditionally-compiled |AssertSanity()|-type method instead, so I would be perfectly happy with a warning for this case. Not sure how prevalent this pattern is though.

yeah we need a similar check for other macros too. I think what we want is a must_be_pure() marker on code and pure annotations on various methods that are pure enough