Linker error with u32::to_ne_bytes and map

[ejmount]

I tried this code (playground example)

#![allow(incomplete_features)]
#![feature(const_generics)]

pub fn main() {
    // this causes a linker error if const_generics is enabled
    let _ = [0; 1].map(u32::to_ne_bytes);
    
    // but this does not!
    //let _ = [0; 1].map(|x| u32::to_ne_bytes(x));
}

I expected to see this happen: a compile error. And also, I particularly expect map(foo) and map(|x| foo(x)) to behave similarly.

Instead, this happened: the linker falls over:

error: linking with `cc` failed: exit status: 1
  |
  = note: "cc" "-m64" "/playground/target/debug/deps/playground-4c173013dcdff931.playground.8c85a93c-cgu.0.rcgu.o" "/playground/target/debug/deps/playground-4c173013dcdff931.12vh8z6qs538xs91.rcgu.o" "-Wl,--as-needed" "-L" "/playground/target/debug/deps" "-L" "/playground/target/debug/build/libsqlite3-sys-0d351e27eaa1e97b/out" "-L" "/playground/target/debug/build/ring-38bf9793e960dc3f/out" "-L" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-03b16363306a53dd.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-4695c0f6311791db.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-1a282f8b292d9e3f.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-a54ae5159230894d.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-13671d003abcccd5.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-7509adad918d4b3b.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-66d0be1f7efaf5ca.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-41443b46a1557b2c.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-60812e99072283ff.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-412d545269c27063.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-0dbc7e011696d844.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-78b2343cc72ff57a.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-65fa19680bfb5ee4.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-72cab8079f9b3b1e.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-32d13a5363efe47b.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-9ee1d5d15e6abbeb.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-52d5241975807511.rlib" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-9924c22ae1efcf66.rlib" "-Wl,--end-group" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-96219fb718f2f3e8.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/playground/target/debug/deps/playground-4c173013dcdff931" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs"
  = note: /usr/bin/ld: /playground/target/debug/deps/playground-4c173013dcdff931.playground.8c85a93c-cgu.0.rcgu.o: in function `core::array::collect_into_array':
          /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:506: undefined reference to `core::mem::maybe_uninit::MaybeUninit<T>::uninit_array'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:485: undefined reference to `core::mem::zeroed'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:508: undefined reference to `core::mem::maybe_uninit::MaybeUninit<T>::slice_as_mut_ptr'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:515: undefined reference to `core::slice::<impl [T]>::get_unchecked_mut'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:515: undefined reference to `core::mem::maybe_uninit::MaybeUninit<T>::write'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:521: undefined reference to `core::mem::forget'
          /usr/bin/ld: /rustc/5d6804469d80aaf26f98090ae016af45e267f58f/library/core/src/array/mod.rs:525: undefined reference to `core::mem::maybe_uninit::MaybeUninit<T>::array_assume_init'
          /usr/bin/ld: /playground/target/debug/deps/playground-4c173013dcdff931: hidden symbol `_ZN4core5slice29_$LT$impl$u20$$u5b$T$u5d$$GT$17get_unchecked_mut17hab68e22870af8369E' isn't defined
          /usr/bin/ld: final link failed: bad value
          collect2: error: ld returned 1 exit status
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

[hellow554]

It looks like you are using an oder version of rustc? Can you post your version please (rustc -vV). In the meantime, use rustup update to update your compiler.

I can't see the error anymore on the latest nightly

Wow, this is funny!

So feature(const_generics) is now "removed" (in #88369) and replaced by either adt_const_params or generic_const_exprs. If you choose the first, the program will compile fine and gives no warning and even runs as intended.

But if you choose the later, the program will error out with the exact same message as @ejmount described.

Second fun fact, if the second map isn't commeted out (and the still one is still in place) the program will compile fine in both configurations.

[Rain336]

Sounds to me like a monomorpization problem! It seams like the first example doesn't create a monomorpized version of the u32::to_ne_bytes function, but still references it! That would also explain why it would work if the second example is enabled, since that one would correctly generate a monomorpized version of u32::to_ne_bytes, which can then be used by the first example!

[fmease]

I can no longer reproduce this even if I follow

So feature(const_generics) is now "removed" (in #88369) and replaced by either adt_const_params or generic_const_exprs. If you choose the first, the program will compile fine and gives no warning and even runs as intended.

Closing as fixed. Please ping me if I missed anything.