Remove some unused crate dependencies.

[nnethercote]

I found these by setting the unused_crate_dependencies lint temporarily to Warn.

r? @jackh726

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

This PR changes Stable MIR

cc @oli-obk, @celinval, @ouz-a

[nnethercote]

There's an argument to be made that we should add #[deny(unused_crate_dependencies)] to most of the crates in the compiler, but I haven't done that here.

[jackh726]

Can you make an MCP to change the lint to deny?

[jackh726]

This change seems weird?

[jackh726]

Why this change?

[mati865]

I think it could be enabled in in [lints] section of Cargo.toml. This should be more manageable than adding deny to each lib.rs.

[nnethercote]

Something I didn't say is that when I enabled it universally I had to deal with several annoying cases, mostly in library/.

• Some crates are only used in certain configurations.
• Some crates are in Cargo.toml because of weird packaging reasons. E.g.

  rust/compiler/rustc/Cargo.toml

  Lines 9 to 20 in e1ac0fa

  	# Make sure rustc_codegen_ssa ends up in the sysroot, because this
  	# crate is intended to be used by codegen backends, which may not be in-tree.
  	rustc_codegen_ssa = { path = "../rustc_codegen_ssa" }
  	rustc_driver = { path = "../rustc_driver" }
  	rustc_driver_impl = { path = "../rustc_driver_impl" }
  	# Make sure rustc_smir ends up in the sysroot, because this
  	# crate is intended to be used by stable MIR consumers, which are not in-tree.
  	rustc_smir = { path = "../rustc_smir" }
  	stable_mir = { path = "../stable_mir" }

These need use rustc_foo as _; items to avoid the warning, or some fiddling with conditional compilation stuff. Both of the cases you asked about above were leftovers for that kind of thing that I failed to removed.

So my conclusion is that this would be good to enable for almost every compiler crate (except the rustc crate), but not library/. There are also these false positive cases:

rust/compiler/rustc_lint_defs/src/builtin.rs

Lines 533 to 539 in e1ac0fa

	/// This lint is "allow" by default because it can provide false positives
	/// depending on how the build system is configured. For example, when
	/// using Cargo, a "package" consists of multiple crates (such as a
	/// library and a binary), but the dependencies are defined for the
	/// package as a whole. If there is a dependency that is only used in the
	/// binary, but not the library, then the lint will be incorrectly issued
	/// in the library.

So I think changing it to Deny in general is not a good idea.

[nnethercote]

I think it could be enabled in in [lints] section of Cargo.toml. This should be more manageable than adding deny to each lib.rs.

I tried adding this to the top level Cargo.toml:

[workspace.lints.rust]
unused_crate_dependencies = "warn"

and it had no effect, even on a stage 2 build. I also tried without the workspace. but then I got a Cargo error. Any other suggestions? I'm no expert on Cargo and workspaces.

[mati865]

When you add it to the workspace, you also have to enable lints inheritance in each member:

[lints]
workspace = true

https://doc.rust-lang.org/cargo/reference/workspaces.html#the-lints-table

[bors]

☔ The latest upstream changes (presumably #126108) made this pull request unmergeable. Please resolve the merge conflicts.

[nnethercote]

I rebased.

[jackh726]

@bors r+

As much as I am wary about landing one-off changes like this without also linting to prevent similar PRs in the future, sounds like there are real reasons we can't lint (at the moment at least). So, I'm fine to land this.

[bors]

📌 Commit 29629d0 has been approved by jackh726

It is now in the queue for this repository.

[jackh726]

(I would still recommend following up with linting for compiler crates if possible)

[nnethercote]

When you add it to the workspace, you also have to enable lints inheritance in each member:

Would I have to make that change to the Cargo.toml file of every rustc_* crate under compiler/? If so, that's worse than adding a single #![deny(unused_crate_dependencies)] line to every lib.rs file.