Combining `[patch]` and `-Zbuild-std` logs that patches are unused even when they are

[Nemo157]

Problem

When building a project that has [patch]es configured with -Zbuild-std cargo will log warnings that those patches are unused, even when they are used.

Steps

> cargo new foo && cd foo
    Creating binary (application) `foo` package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

> cargo add serde
    Updating crates.io index
      Adding serde v1.0.203 to dependencies
    Updating crates.io index
     Locking 7 packages to latest compatible versions

> mkdir .cargo

> echo '[patch.crates-io]\nserde.git = "https://github.com/serde-rs/serde"' > .cargo/config.toml

> cargo check
    Updating git repository `https://github.com/serde-rs/serde`
     Locking 2 packages to latest compatible versions
      Adding serde v1.0.203 (https://github.com/serde-rs/serde#7aafa263)
      Adding serde_derive v1.0.203 (https://github.com/serde-rs/serde#7aafa263)
    Checking foo v0.1.0 (/tmp/scratch.rust-unwrapped.2024-06-03T15-10.uk9NtZ/foo)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s

> cargo check -Zbuild-std --target x86_64-unknown-linux-gnu
    Updating git repository `https://github.com/serde-rs/serde`
warning: Patch `serde v1.0.203 (https://github.com/serde-rs/serde#7aafa263)` was
not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
    Checking foo v0.1.0 (/tmp/scratch.rust-unwrapped.2024-06-03T15-10.uk9NtZ/foo)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.20s

Possible Solution(s)

Probably remove the patches from the context while building the sysroot, I wonder if this actually allows patching std's dependencies currently 🤔.

Notes

No response

Version

cargo 1.80.0-nightly (0de7f2ec6 2024-05-17)
release: 1.80.0-nightly
commit-hash: 0de7f2ec6c39d68022e6b97a39559d2f4dbf3930
commit-date: 2024-05-17
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: NixOS 24.5.0 [64-bit]