Compile warning while compiling libstd with Xargo (use of #[allow_internal_unstable])

[johnthagen]

I am seeing a build warning when building libstd in a simple "Hello World" using Xargo.

     Running `rustc --crate-name std /home/travis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/lib.rs --color always --crate-type dylib --crate-type rlib --emit=dep-info,link -C prefer-dynamic -C opt-level=z -C panic=abort -C codegen-units=1 -C metadata=6a8dec85bcef7069 --out-dir /tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps -L dependency=/tmp/xargo.5pshJ0HoG6fd/target/release/deps --extern alloc=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/liballoc-e8747074132386de.rlib --extern compiler_builtins=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/libcompiler_builtins-8346f6da3599dc11.rlib --extern core=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/libcore-54d405ee7be45efa.rlib --extern libc=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/liblibc-ba56a133f24710be.rlib --extern panic_abort=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/libpanic_abort-e431905f180ae625.rlib --extern rustc_demangle=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/librustc_demangle-cfd6040da80adc90.rlib --extern rustc_asan=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/librustc_asan-6890241a7ab63939.rlib --extern rustc_lsan=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/librustc_lsan-a6443c9ae07827d9.rlib --extern rustc_msan=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/librustc_msan-3ad28f250536833b.rlib --extern rustc_tsan=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/librustc_tsan-c59201cb2ed07266.rlib --extern unwind=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/deps/libunwind-420cd95ff7b95cd4.rlib --sysroot /home/travis/.xargo/HOST -Z force-unstable-if-unmarked -l dl -l rt -l pthread -L native=/tmp/xargo.5pshJ0HoG6fd/target/x86_64-unknown-linux-gnu/release/build/compiler_builtins-6b448c751373bea5/out`
warning: allow_internal_unstable expects list of feature names. In the future this will become a hard error. Please use `allow_internal_unstable(foo, bar)` to only allow the `foo` and `bar` features
  --> /home/travis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/../stdsimd/crates/std_detect/src/detect/arch/x86.rs:82:1
   |
82 | #[allow_internal_unstable]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^

Full build job: https://travis-ci.org/johnthagen/min-sized-rust/jobs/494234235

Project source: https://github.com/johnthagen/min-sized-rust/tree/master/xargo

Build command (using latest nightly):

https://github.com/johnthagen/min-sized-rust/blob/master/.travis.yml#L32-L34

$ rustup component add rust-src;
$ cargo install xargo --force;
$ xargo build --target x86_64-unknown-linux-gnu --release --verbose

[Mark-Simulacrum]

cc @oli-obk - #58098

I suspect this just needs a nightly update to happen but not sure.

[johnthagen]

And for quick reference, the nightly version used in the build was:

$ rustc --version
rustc 1.34.0-nightly (a9410cd1a 2019-02-15)

[oli-obk]

yea this will go away after we get a bootstrap compiler update and then are able to update stdsimd

[Mark-Simulacrum]

In that case I'm going to close as tracking this separately seems not that useful (we'll do both of those naturally anyway); it's only a warning anyway.