Filesystem-oriented flags: sad, messy and not going away

Consider for example the Iterator trait in Rust. People expect code written using iterators to compile down to something that you would find hard to distinguish from a C for loop in disassembly, which requires the compiler to inline a whole bunch of calls to tiny functions and remove some intermediate values. And not all those tiny functions have to come from the same library, they can come from many different ones, and many will have generic arguments or callbacks with generic arguments from still other libraries.

And it's not just Iterator, the same goes for asynchronous I/O using Futures, and probably more absolutely core functionality that I'm forgetting about right now. As soon as parts of that become dynamically linked, you start having to make some really tough calls about what the compiler can statically assume and optimize out.