This is something I do wish Rust could better support. A `#![no_std]` library crate can at least discourage allocation (although it can always `extern crate alloc;` in lib.rs or invoke malloc via FFI...)

▲ maxbond 15 hours ago | parent [-]

Is the juice worth the squeeze to introduce two new function colors? What would you do if you needed to call `unreachable!()`?

It's a shame that you can't quite do this with a lint, because they can't recurse to check the definitions of functions you call. That would seem to me to be ideal, maintain it as an application-level discipline so as not to complicate the base language, but automate it.

▲ MaulingMonkey 14 hours ago | parent [-]

> Is the juice worth the squeeze to introduce two new function colors?

Typically no... which is another way of saying occasionally yes.

> What would you do if you needed to call `unreachable!()`?

Probably one of e.g.:

    unsafe { core::hint::unreachable_unchecked() }
    loop {}

Which are of course the wrong habits to form! (More seriously: in the contexts where such no-panic colors become useful, it's because you need to not call `unreachable!()`.)

> It's a shame that you can't quite do this with a lint, because they can't recurse to check the definitions of functions you call. That would seem to me to be ideal, maintain it as an application-level discipline so as not to complicate the base language, but automate it.

Indeed. You can mark a crate e.g. #![deny(clippy::panic)] and isolate that way, but it's not quite the rock solid guarantees Rust typically spoils us with.

	▲	VorpalWay 8 hours ago \| parent [-]
		> Typically no... which is another way of saying occasionally yes. You might be able to avoid generating panic handling landing pads if you know that a function does not call panic (transitively). Inlining and LTO often help, but there is no guarantee that it will be possible to elide, it depends on the whims of the optimiser. Knowing that panicking doesn't happen can also enable other optimisations that wouldn't have been correct if a panic were to happen. All of that is usually very minor, but in a hot loop it could matter, and it will help with code size and density. (Note that this is assuming SysV ABI as used by everyone except Windows, I have no clue how SEH exceptions on Windows work.) > Indeed. You can mark a crate e.g. #![deny(clippy::panic)] and isolate that way, but it's not quite the rock solid guarantees Rust typically spoils us with. Also, there are many things in Rust which can panic apart from actual calls to panic or unwrap: indexing out of bounds, integer overflow (in debug), various std functions if misused, ...