can't reproduce build with a custom target

[shkoo]

Problem

When compiling to a custom target based on a JSON target spec, Cargo seems to hash the full pathname of the JSON target spec into its metadata hash. This makes it very difficult to reproduce these builds on different machines with different filesystem layouts.

Ideally builds could be reproducible no matter what the full pathname is of the JSON target spec.

Steps

cargo new path-repro
cd path-repro
for i in a b
do
    mkdir $i
    rustc --print=target-spec-json -Z unstable-options |grep -v is-builtin > $i/x86_64-unknown-linux-gnu.json
    cargo +nightly rustc --release --target-dir=build-$i --target=$i/x86_64-unknown-linux-gnu.json -Z build-std -- --emit=asm
done
diff -u build-?/*/release/deps/path_repro*.s

Possible Solution(s)

I think this should be fixed by #10746

Notes

No response

Version

$ cargo version --verbose
cargo 1.63.0-nightly (4d92f07f3 2022-06-09)
release: 1.63.0-nightly
commit-hash: 4d92f07f34ba7fb7d7f207564942508f46c225d3
commit-date: 2022-06-09
host: x86_64-unknown-linux-gnu
libgit2: 1.4.2 (sys:0.14.2 vendored)
libcurl: 7.83.1-DEV (sys:0.4.55+curl-7.83.1 vendored ssl:OpenSSL/1.1.1n)
os: Ubuntu 20.04 (focal) [64-bit]

[weihanglo]

Fixed with #10746