`cargo --config` doesn't (seem) to work with `lints.*`

[kristof-mattei]

Problem

I'm trying to set up a separate linting strategy for local development with everything as a warning, but still allow me to compile. Who cares about dead code / unused imports when I'm iterating over a feature? I'll tidy up later.

But on the the CI I want things dialed up to the max.

With the release of lints support in Rust 1.74 I've been trying to get it to work together with --config <PATH> / --config KEY=VALUE, and I've not been successful.

Steps

1. cargo new lint-config
2. Put the following in src/main.rs:

   fn main() {
       let vârïàblê = "non-ascii";
   
       println!("Hello, {}!", vârïàblê);
   }

3. Put the following in ci.toml:

   [lints.rust]
   non_ascii_idents="deny"

4. Try and build with
   • cargo --config "lints.rust.non_ascii_idents = \"deny\"" build
   • cargo --config lints.rust.non_ascii_idents=\"deny\" build
   • cargo --config "lints.rust.non_ascii_idents='deny'" build
   • cargo --config 'lints.rust.non_ascii_idents="deny"' build
   • cargo --config ci.toml build
     In all situations I've tried forbid instead of deny, and moving build before config.
5. Notice that in none of the builds we get a failure, even though we expect it to.

Possible Solution(s)

No response

Notes

1. Moving the lint from ci.toml to Cargo.toml and building with cargo build produces the expected result:

   kristof@NOSTROMO:~/lint-config$ cargo build
      Compiling lint-config v0.1.0 (/home/kristof/lint-config)
   error: identifier contains non-ASCII characters
    --> src/main.rs:2:9
     |
   2 |     let vârïàblê = "non-ascii";
     |         ^^^^^^^^
     |
     = note: requested on the command line with `-D non-ascii-idents`
   
   error: could not compile `lint-config` (bin "lint-config") due to previous error    

2. Making sure this is supported I tried with cargo --config build.target-dir=\"somewhere-else\" build which changes the target dir & works as expected.

Version

cargo 1.74.0 (ecb9851af 2023-10-18)
release: 1.74.0
commit-hash: ecb9851afd3095e988daaa35a48bc7f3cb748e04
commit-date: 2023-10-18
host: x86_64-unknown-linux-gnu
libgit2: 1.7.1 (sys:0.18.0 vendored)
libcurl: 8.4.0-DEV (sys:0.4.68+curl-8.4.0 vendored ssl:OpenSSL/1.1.1u)
ssl: OpenSSL 1.1.1u  30 May 2023
os: Ubuntu 23.10 (mantic) [64-bit]

[weihanglo]

--config CLI arg is for setting cargo configuration value, i.e. .cargo/config.toml. It is not for Cargo.toml.

[weihanglo]

Here is the strategy rust-lang/cargo itself uses currently.

Set lint rules for development in Cargo.toml:

cargo/Cargo.toml

Lines 109 to 121 in 71cd3a9

	[workspace.lints.rust]
	rust_2018_idioms = "warn" # TODO: could this be removed?
	[workspace.lints.rustdoc]
	private_intra_doc_links = "allow"
	[workspace.lints.clippy]
	all = { level = "allow", priority = -1 }
	dbg_macro = "warn"
	disallowed_methods = "warn"
	print_stderr = "warn"
	print_stdout = "warn"
	self_named_module_files = "warn"

-D warnings in CI as a separate job. Note that -D warnings is set just because rust-lang/cargo only warns on a really small set of clippy rules. Generally speaking -D warnings is not recommended as it might break your CI bewteen Rust releases.

cargo/.github/workflows/main.yml

Line 69 in 71cd3a9

- run: cargo clippy --workspace --all-targets --no-deps -- -D warnings

[kristof-mattei]

Okay so if I understand correctly, -D warnings or --deny=warnings turns all warnings into deny.

It does not mean that there is a table with lints named warnings that are now denied (like -Dclippy::pedantic)?

[weihanglo]

Not exactly. For -D warnings it is set warnings lint group as denied.

To set rustc built-in lints in [lints] in Cargo.toml, specify them under [lints.rust] table. See this doc for more. Basically, the syntax is like:

[lints.<tool>]
lint-rule-name = "<level>"

I am going to close this, as it is not about bugs in Cargo. Feel free to open new issues for any doc enhancement idea.

[epage]

Generally speaking -D warnings is not recommended as it might break your CI bewteen Rust releases.

Clarification: setting that in CI is the recommended way but you likely want to pin to a specific rust release. I use my MSRV.