`CARGO_UNSTABLE_BUILD_STD` doesn't support multiple crates anymore

[Nemo157]

Problem

> CARGO_UNSTABLE_BUILD_STD=std,panic_abort cargo run
error: invalid character `,` in package name: `std,panic_abort`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)

This works via the CLI arg:

> cargo run -Zbuild-std=std,panic_abort
...
   Compiling std v0.0.0 (/nix/store/gyinl9bb727ajna53pwz034xazca9aqz-rust-minimal-1.85.0-nightly-2025-01-02/lib/rustlib/src/rust/library/std)
...
   Compiling panic_abort v0.0.0 (/nix/store/gyinl9bb727ajna53pwz034xazca9aqz-rust-minimal-1.85.0-nightly-2025-01-02/lib/rustlib/src/rust/library/panic_abort)
...
Hello, world!

Tested on cargo 1.85.0-nightly (d73d2caf9 2024-12-31). This used to work via the env-var too, I didn't fully bisect but at least in cargo 1.84.0-nightly (e75214ea4 2024-10-25) it worked.

Steps

No response

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.85.0-nightly (d73d2caf9 2024-12-31)
release: 1.85.0-nightly
commit-hash: d73d2caf9e41a39daf2a8d6ce60ec80bf354d2a7
commit-date: 2024-12-31
host: x86_64-unknown-linux-gnu
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: NixOS 24.11.0 [64-bit]

[ehuss]

Thanks for the report!

@weihanglo This seems to have regressed from #14899. Is there a reason that removed the comma splitting?

[weihanglo]

No. It was an overlook