`unused_imports` lint help on module named `tests_*` too assertive and potentially confusing

[jieyouxu]

Code

mod tests_revision_unpaired_stdout_stderr {
    use std::ptr;
}

fn main() {}

Current output

warning: unused import: `std::ptr`
 --> src/main.rs:2:9
  |
2 |     use std::ptr;
  |         ^^^^^^^^
  |
help: consider adding a `#[cfg(test)]` to the containing module
 --> src/main.rs:1:1
  |
1 | mod tests_revision_unpaired_stdout_stderr {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = note: `#[warn(unused_imports)]` on by default

Desired output

warning: unused import: `std::ptr`
 --> src/main.rs:2:9
  |
2 |     use std::ptr;
  |         ^^^^^^^^
  |
help: if this is a test module, consider adding a `#[cfg(test)]` to the containing module
 --> src/main.rs:1:1
  |
1 | mod tests_revision_unpaired_stdout_stderr {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = note: `#[warn(unused_imports)]` on by default

Rationale and extra context

This help message seems weird. I'd expect the help to be more like:

• Consider adding #[allow(unused_imports)] if you want to silent the lint on the unused import
• Consider removing the unused import

Suggesting to add #[cfg(test)] to the module is the least expected option, and it seems too assertive in its current wording.

Other cases

No response

Rust Version

rustc 1.78.0-nightly (bb594538f 2024-02-20)
binary: rustc
commit-hash: bb594538fc6e84213a6b8d5e165442570aa48923
commit-date: 2024-02-20
host: x86_64-apple-darwin
release: 1.78.0-nightly
LLVM version: 18.1.0

Anything else?

Perhaps the detection for triggering #[cfg(test)] on the module could be smarter and only consider a module as a potential test module if it contains at least one #[test] annotated function?

[Redidacove]

How can i proceed to solve this any suggestions on how can it be done changes to which file will make it happen since i am new to this repo

[jieyouxu]

Hi @Redidacove, thank you for your interest. For now, I think making the help message less assertive would be sufficient. Here are some tips to get you started:

1. You will need to find where this help message is emitted.

You can identify where this help message is coming from by grepping the repo, i.e.

$ rg --no-ignore --fixed-strings "consider adding a `#[cfg(test)]` to the containing module" compiler 
compiler/rustc_lint/src/context/diagnostics.rs
111:                    "consider adding a `#[cfg(test)]` to the containing module",

2. In this case, it might be as simple as changing this string to make it sound less assertive.
3. You can reformat your changes via ./x fmt.
4. Run the UI test suite to make sure at least one test fails -- this means at least one test is actually testing this diagnostic.
5. If you're happy with the stderr output from your change, re-bless the UI test suite and now make sure the UI test suite passes.
6. Run ./x test tidy to make sure tidy checks passes locally.

$ ./x test tests/ui --stage 1 --bless

7. Submit a PR and wait for review. Your reviewer will discuss with you to see if any further changes are desirable.

https://rustc-dev-guide.rust-lang.org/ is the more in-depth reference. If you are stuck, feel free to ask here, or make a new thread in #t-compiler/help.

[Suya1671]

@rustbot claim

[Suya1671]

(Unless @Redidacove already submitted a change and I didn't find it, I should be able to create a PR soon)