`std` wanted features & bugfixes

[ojeda]

Note: there is the "A-rust-for-linux" label in the rust repository: https://github.com/rust-lang/rust/labels/A-rust-for-linux.

Features that we would like to see

Required (we almost certainly want them)

Nice to have (not critical, we could workaround if needed, etc.)

Low priority (we will likely not use them in the end)

• Make test not depend on std.
  • TODO: try out #![test_runner] + #![reexport_test_harness_main] as suggested by @bjorn3: std wanted features & bugfixes #572 (comment).
  • It would require customizing whatever test needs from std at the moment.
  • It would avoid having to build std for tests.
  • It would allow to run tests in kernel space ("#[test(kernel)]").
  • It would avoid having to wait for Cargo's -Zbuild-std fixes & stabilization.

Done (stabilized, fixed, not needed anymore, etc.)

• A way to customize/override the dependency graph in -Zbuild-std to use our custom alloc etc.

  • alloc was dropped, so we do not need it anymore.
  • Related issue: Custom source standard library rust-lang/wg-cargo-std-aware#7.
  • Related issue: Can we tailor the version of the compiler-builtins package that is compiled and linked together with the core crate? rust-lang/wg-cargo-std-aware#61.

• A way to use -Zbuild-std for building custom sysroots (and not packages).

  • We do not use -Zbuild-std anymore.

---

Bugs that we would like to see fixed

Required (we almost certainly want them)

Nice to have (probably not critical, we could workaround if needed, etc.)

Low priority (we will likely not use them in the end)

Done (stabilized, fixed, or not needed anymore, etc.)

[bjorn3]

Make test not depend on std.

For no-std testing there is the unstable #![test_runner] + #![reexport_test_harness_main]. This was implemented in rust-lang/rust#53410. See https://os.phil-opp.com/testing/ for an example. To copy the example there:

#![feature(custom_test_frameworks)]
#![test_runner(crate::test_runner)]
#![reexport_test_harness_main = "test_main"]

#[cfg(test)]
fn test_runner(tests: &[&dyn Fn()]) {
    println!("Running {} tests", tests.len());
    for test in tests {
        test();
    }
}

#[no_mangle]
pub extern "C" fn _start() -> ! {
    println!("Hello World{}", "!");

    #[cfg(test)]
    test_main();

    loop {}
}

#[test_case]
fn trivial_assertion() {
    print!("trivial assertion... ");
    assert_eq!(1, 1);
    println!("[ok]");
}

I believe I have already linked it before by the way.

[ojeda]

Thanks! I think you did, yeah. Linked in the list to avoid missing it again :)

I was filling this one to keep track of some of the bits from the meeting the other day that were not yet in the list.