build.rs

#![allow(unknown_lints, clippy::undocumented_unsafe_blocks)]

#[::rustversion::since(1.80)]
fn rustc_cfg() {
    println!("cargo:rustc-check-cfg=cfg(nightly)");
}
#[::rustversion::before(1.80)]
fn rustc_cfg() {
    // noop
}

#[::rustversion::nightly]
#[allow(dead_code)]
const fn is_nightly() -> bool {
    true
}
#[::rustversion::not(nightly)]
#[allow(dead_code)]
const fn is_nightly() -> bool {
    false
}

fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rerun-if-changed=src/ffi/c/calloca.c");

    let failures = run_checks();
    if failures.is_empty() {
        // all success, now enable "nightly" if on the nightly toolchain
        rustc_cfg();
        #[cfg(not(feature = "no_nightly"))]
        if is_nightly() {
            println!("cargo:rustc-cfg=nightly");
        }
        #[cfg(feature = "stack_alloc")]
        {
            if let Err(e) = cc::Build::new().file("src/ffi/c/calloca.c").try_compile("calloca") {
                panic!("failed to compile calloca.c: {}", e);
            }
        }

        return;
    }

    for Failure { source, code, msg } in &failures {
        eprintln!("UB test {}:{} failed: {}", source, code, msg);
    }

    let example_toolchain = "nightly-x86_64-unknown-linux-gnu 1.91.0 (840b83a10 2025-07-30)";
    let req_info = "please open an issue with your rust toolchain info";
    let get_tc_info = "(`rustup default`, `cargo --version`).";
    panic!(
        "UB checks failed (codes: {:?}).\n{} {}\nexample: {}",
        failures.iter().map(|f| f.code).collect::<Vec<_>>(),
        req_info,
        get_tc_info,
        example_toolchain
    );
}

pub struct Failure {
    source: usize,
    code: usize,
    msg: &'static str
}

fn run_checks() -> Vec<Failure> {
    let mut failures = Vec::new();

    failures.extend(checks::sp_frp::check());

    failures
}

mod checks {
    pub mod sp_frp {
        use {crate::Failure, ::core::ptr::NonNull};

        #[cfg_attr(miri, track_caller)]
        pub fn check() -> Vec<Failure> {
            let mut failures = Vec::<Failure>::new();
            let i = 4;

            let mut data: Vec<usize> = (0..i).map(|j| 64 << j).collect();
            let slice: &mut [usize] = &mut data;

            let ptr = slice.as_mut_ptr();
            let len = slice.len();

            let slice_ptr = slice_ptr_from_parts(ptr, len);

            // check that they dereference to the same thing
            if unsafe { &*slice_ptr } != slice {
                failures.push(Failure {
                    source: 0,
                    code: 0,
                    msg: "result doesn't dereference properly"
                });
            }
            // check that they have the same pointer and length
            if slice.as_ptr() != slice_ptr.cast::<usize>() {
                failures.push(Failure {
                    source: 0,
                    code: 1,
                    msg: "result doesn't have the same pointer"
                });
            }
            if unsafe { slice_ptr.as_ref() }.unwrap().len() != len {
                failures.push(Failure {
                    source: 0,
                    code: 2,
                    msg: "result doesn't have the same length"
                });
            }

            unsafe {
                if len
                    != nonnull_slice_len(nonnull_slice_from_parts(NonNull::new_unchecked(ptr), len))
                {
                    failures.push(Failure {
                        source: 0,
                        code: 3,
                        msg: "result doesn't have the correct metadata"
                    });
                }
            }

            for (i, &elem) in slice.iter().enumerate() {
                let via_raw = unsafe { (&*slice_ptr)[i] };
                // check that the values are all the same
                if elem != via_raw {
                    failures.push(Failure {
                        source: 0,
                        code: 4,
                        msg: "values differ between original slice and raw-slice"
                    });
                }

                // manually check that the values are the same
                if via_raw != 64_usize << i {
                    failures.push(Failure {
                        source: 0,
                        code: 5,
                        msg: "raw-slice value mismatch against expected"
                    });
                }
            }

            failures
        }

        // from the crate
        #[cfg_attr(miri, track_caller)]
        #[must_use]
        fn nonnull_slice_len<T>(ptr: NonNull<[T]>) -> usize {
            unsafe { (&*ptr.as_ptr()).len() }
        }

        #[cfg_attr(miri, track_caller)]
        #[must_use]
        fn nonnull_slice_from_parts<T>(p: NonNull<T>, len: usize) -> NonNull<[T]> {
            unsafe { NonNull::new_unchecked(slice_ptr_from_parts(p.as_ptr(), len)) }
        }

        #[cfg_attr(miri, track_caller)]
        #[must_use]
        fn slice_ptr_from_parts<T>(p: *mut T, len: usize) -> *mut [T] {
            unsafe { union_transmute((p, len)) }
        }

        #[cfg_attr(miri, track_caller)]
        unsafe fn union_transmute<Src: Copy, Dst: Copy>(src: Src) -> Dst {
            union Either<Src: Copy, Dst: Copy> {
                src: Src,
                dst: Dst
            }

            Either { src }.dst
        }
    }
}