when using profile overrides for "core" and -Zbuild-std, cargo emits incorrect warning that profile override is unused

[codyps]

Problem

Cargo prints a warning: profile package spec `core` in profile `dev` did not match any packages when a profile.dev.package.core section exists in Cargo.toml.

The options specified in the profile.dev.package.core are used, despite the warning.

Command + verbose output showing that the debug-assertions is passed to rustc:

cody@truman profile-core % cargo +nightly check -Zbuild-std=core --target thumbv7em-none-eabihf --verbose
warning: profile package spec `core` in profile `dev` did not match any packages
   Compiling core v0.0.0 (/Users/cody/Library/Caches/rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/core)
     Running `/Users/cody/.local/bin/sccache-wrapper2 rustc --crate-name core --edition=2021 /Users/cody/Library/Caches/rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 -C debug-assertions=off -C metadata=8c45ea5e23dd0d5b -C extra-filename=-8c45ea5e23dd0d5b --out-dir /Users/cody/p/profile-core/target/thumbv7em-none-eabihf/debug/deps --target thumbv7em-none-eabihf -Z force-unstable-if-unmarked -L dependency=/Users/cody/p/profile-core/target/thumbv7em-none-eabihf/debug/deps -L dependency=/Users/cody/p/profile-core/target/debug/deps --cap-lints allow`

Cargo.toml content:

[package]
name = "profile-core"
version = "0.1.0"
edition = "2021"

[dependencies]

[profile.dev.package.core]
overflow-checks = false
debug-assertions = false

Steps

I've created a sample project here: https://github.com/jmesmon/cargo-bug-profile-core. Run it with the command cargo +nightly check -Zbuild-std=core --target thumbv7em-none-eabihf --verbose or similar.

1. create a cargo lib package
2. make it no_std (makes things easier to reproduce here, but not strictly requried)
3. Add [profile.dev.package.core] debug-assertions = false to the Cargo.toml (or some other profile adjustment)
4. build with cargo +nightly check -Zbuild-std=core --target thumbv7em-none-eabihf --verbose (or similar)
5. note the warning: profile package spec `core` in profile `dev` did not match any packages printed, but the debug-assertions option is passed to rustc.

Notes

This specific issue is mentioned in #10118 (comment). It may be related to #8328 (which also is regarding this warning, but not for core)

Version

cody@truman profile-core % cargo +nightly version --verbose
cargo 1.61.0-nightly (65c826642 2022-03-09)
release: 1.61.0-nightly
commit-hash: 65c82664263feddc5fe2d424be0993c28d46377a
commit-date: 2022-03-09
host: x86_64-apple-darwin
libgit2: 1.4.1 (sys:0.14.1 vendored)
libcurl: 7.77.0 (sys:0.4.51+curl-7.80.0 system ssl:(SecureTransport) LibreSSL/2.8.3)
os: Mac OS 12.2.1 [64-bit]

[ehuss]

Thanks for the detailed report and reproduction! The way profile overrides interact with the standard library hasn't been decided upon. This is being tracked in rust-lang/wg-cargo-std-aware#2, so I'm going to close in favor of that.