Add support for self-contained object files (musl).

[UebelAndre]

In newer rust-std artifacts there is a self-contained directory which contains some .o files. These are currently ignored but without them the rules cannot target musl and users will see a similar linker error:

error: linking with `...`
  |
  = note: `...`
  = note: `...`: error: rct1.o: No such file or directory
          `...`: error: crti.o: No such file or directory
          `...`: error: crtbeginS.o: No such file or directory
          `...`: error: crtendS.o: No such file or directory
          `...`: error: crtn.o: No such file or directory

These files appear to have been introduced in Rust 1.46.0. They seem related to rust-lang/rust#70740 but I'm still not clear what mechanism actually generates and installs these directories in the artifacts.

Regardless, this change addresses these linker issues without impacting other target triples as far as I can tell.

[UebelAndre]

I also wrote this script to find what artifacts contained the self-contained directory and what was inside it. Only musl populates this directory.

#!/bin/bash

set -euo pipefail

MUSL=(
rust-std-1.26.0-aarch64-unknown-linux-musl
rust-std-1.26.0-x86_64-unknown-linux-musl
rust-std-1.36.0-aarch64-unknown-linux-musl
rust-std-1.36.0-aarch64-unknown-linux-musl
rust-std-1.45.0-aarch64-unknown-linux-musl
rust-std-1.45.0-x86_64-unknown-linux-musl
rust-std-1.46.0-aarch64-unknown-linux-musl
rust-std-1.46.0-x86_64-unknown-linux-musl
rust-std-1.53.0-aarch64-unknown-linux-musl
)

OTHER=(
rust-std-1.45.0-x86_64-apple-darwin
rust-std-1.45.0-wasm32-unknown-unknown
rust-std-1.45.0-x86_64-pc-windows-msvc
rust-std-1.46.0-x86_64-apple-darwin
rust-std-1.46.0-wasm32-unknown-unknown
rust-std-1.46.0-x86_64-pc-windows-msvc
)

function find_self_contained() {
    temp_dir="$(mktemp -d -t rust-self-contained)"
    pushd "${temp_dir}"
    for art in ${@}; do
        echo "${art}"
        wget --quiet https://static.rust-lang.org/dist/${art}.tar.gz
        tar -xf "${art}.tar.gz"
        find "${art}" -name "self-contained" -exec tree {} \;
    done
    popd && rm -rf "${temp_dir}"
}

echo "Test MUSL"
find_self_contained ${MUSL[@]}

echo "Test OTHER"
find_self_contained ${OTHER[@]}

Test MUSL
/var/folders/hf/phjl9q7501gb5wt_qr4ltn3m0000gn/T/rust-self-contained.KEpXUBeb ~/Code/rules_rust
rust-std-1.26.0-aarch64-unknown-linux-musl
rust-std-1.26.0-x86_64-unknown-linux-musl
rust-std-1.36.0-aarch64-unknown-linux-musl
rust-std-1.36.0-aarch64-unknown-linux-musl
rust-std-1.45.0-aarch64-unknown-linux-musl
rust-std-1.45.0-x86_64-unknown-linux-musl
rust-std-1.46.0-aarch64-unknown-linux-musl
rust-std-1.46.0-aarch64-unknown-linux-musl/rust-std-aarch64-unknown-linux-musl/lib/rustlib/aarch64-unknown-linux-musl/lib/self-contained
├── Scrt1.o
├── crt1.o
├── crti.o
├── crtn.o
└── rcrt1.o

0 directories, 5 files
rust-std-1.46.0-x86_64-unknown-linux-musl
rust-std-1.46.0-x86_64-unknown-linux-musl/rust-std-x86_64-unknown-linux-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained
├── Scrt1.o
├── crt1.o
├── crti.o
├── crtn.o
└── rcrt1.o

0 directories, 5 files
rust-std-1.53.0-aarch64-unknown-linux-musl
rust-std-1.53.0-aarch64-unknown-linux-musl/rust-std-aarch64-unknown-linux-musl/lib/rustlib/aarch64-unknown-linux-musl/lib/self-contained
├── Scrt1.o
├── crt1.o
├── crtbegin.o
├── crtbeginS.o
├── crtend.o
├── crtendS.o
├── crti.o
├── crtn.o
└── rcrt1.o

0 directories, 9 files
~/Code/rules_rust
Test OTHER
/var/folders/hf/phjl9q7501gb5wt_qr4ltn3m0000gn/T/rust-self-contained.0crH80lq ~/Code/rules_rust
rust-std-1.45.0-x86_64-apple-darwin
rust-std-1.45.0-wasm32-unknown-unknown
rust-std-1.45.0-x86_64-pc-windows-msvc
rust-std-1.46.0-x86_64-apple-darwin
rust-std-1.46.0-x86_64-apple-darwin/rust-std-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/self-contained

0 directories, 0 files
rust-std-1.46.0-wasm32-unknown-unknown
rust-std-1.46.0-wasm32-unknown-unknown/rust-std-wasm32-unknown-unknown/lib/rustlib/wasm32-unknown-unknown/lib/self-contained

0 directories, 0 files
rust-std-1.46.0-x86_64-pc-windows-msvc
rust-std-1.46.0-x86_64-pc-windows-msvc/rust-std-x86_64-pc-windows-msvc/lib/rustlib/x86_64-pc-windows-msvc/lib/self-contained

0 directories, 0 files

[UebelAndre]

Also, I'm not sure how to add a test for musl... The changes here work though 😅

[illicitonion]

I don't feel like I have enough context to really review this (or indeed to suggest how to test it on CI), but in general the change looks reasonable? If anyone has more context, it'd be great for them to review, otherwise I can somewhat unknowingly approve...

[hlopko]

Is there a way we could have a test?

[UebelAndre]

Is there a way we could have a test?

I had the same question (#829 (comment)) and opened bazelbuild/continuous-integration#1190 to try and answer it. Any suggestions?