clippy::cargo lint is applied to sibling crates

[purplesyringa]

Summary

When #[warn(clippy::cargo)] is enabled in one crate in a workspace, warnings are emitted for other crates in the same workspace too.

Reproducer

I tried this code:

.
├── a
│  ├── Cargo.toml
│  └── src
│     └── main.rs
├── b
│  ├── Cargo.toml
│  └── src
│     └── main.rs
├── Cargo.lock
└── Cargo.toml

a/src/main.rs:

#![warn(clippy::cargo)]

fn main() {
    println!("Hello, world!");
}

b/src/main.rs:

fn main() {
    println!("Hello, world!");
}

I expected to see this happen: cargo clippy emits warnings for a but not b

Instead, this happened: cargo clippy emits warnings for both a and b

Version

rustc 1.84.0-nightly (1e4f10ba6 2024-10-29)
binary: rustc
commit-hash: 1e4f10ba6476e48a42a79b9f846a2d9366525b9e
commit-date: 2024-10-29
host: x86_64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.1

Additional Labels

No response

[blyxyas]

I've tested this, and seems that it doesn't lint on sibling crates anymore =^w^= do you have another example or do we close this as completed?

[purplesyringa]

It's still kind of broken, though the reproducer gets a bit uglier.

$ tree
.
├── a
│   ├── Cargo.toml
│   └── src
│       └── lib.rs
├── b
│   ├── Cargo.toml
│   └── src
│       └── lib.rs
├── Cargo.lock
└── Cargo.toml

Workspace-level Cargo.toml enables the lint:

[workspace]
members = ["a", "b"]
resolver = "2"

[workspace.lints.clippy]
cargo = "warn"

Crate A disables the lint in a/src/lib.rs:

#![allow(clippy::cargo)]

Crate B's lib.rs is empty.

cargo clippy warns about missing metadata fields for both A and B even though the lint is disabled for A.

---

More data: if the lints are disabled for both A and B, no warnings are shown. If neither A nor B disable the lints, lints are obviously emitted for both A and B, but: Clippy emits 12 warnings in total (so 6 for A and 6 for B) and then says

warning: `a` (lib) generated 12 warnings
warning: `b` (lib) generated 12 warnings (12 duplicates)

So what I think happening is that linting one crate emits warnings for all crates, and the "12 duplicates" here demonstrates this quadratic behavior.

[purplesyringa]

Looks like the whole clippy::cargo lint namespace is cursed. I'm assuming that LateLintPass::check_crate is invoked for each crate individually, but then common_metadata::check iterates over each package, but the same applies to feature_name, too. lint_groups_priority reads Cargo.toml directly, and I don't know if that's correct, multiple_crate_versions works correctly but has superquadratic time complexity because it sorts packages on each iteration for some reason, and wildcard_dependencies only lints the first package.