Doc-tests do not respect linker settings

[madonuko]

Problem

Doc-test in cargo test --doc and cargo test does not respect linker settings in ~/.cargo/config.toml.

Steps

1. Paste the following file into ~/.cargo/config.toml:

[target.x86_64-unknown-linux-gnu]
#linker = "gcc"
rustflags = ["-C", "link-arg=-fuse-ld=mold"]

2. Make any doc-test, whatever you like, then run cargo test --doc
3. Notice during normal test compilation and cargo build, mold is used, but not for doc-tests
4. uncomment linker = "gcc", try again (same behaviour)
5. use linker = "clang", try again (same behaviour)

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.79.0 (ffa9cf99a 2024-06-03)
release: 1.79.0
commit-hash: ffa9cf99a594e59032757403d4c780b46dc2c43a
commit-date: 2024-06-03
host: x86_64-unknown-linux-gnu
libgit2: 1.7.2 (sys:0.18.3 vendored)
libcurl: 8.6.0-DEV (sys:0.4.72+curl-8.6.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Ultramarine Linux 40.0.0 (lostumbrella) [64-bit]

[ehuss]

Thanks for the report! I believe this is a duplicate of #12532 and #7040, so closing in favor of those.

You can use -Zdoctest-xcompile on nightly to honor the linker flag.
For rustflags, you need to also specify rustdocflags. Conceptually, doctests are going through rustdoc which has a different field for specifying its flags.