Fix items_after_test_module for non root modules, add applicable suggestion

[Alexendoo]

Fixes #11050
Fixes #11153

changelog: [items_after_test_module]: Now suggests a machine-applicable suggestion.
changelog: [items:after_test_module]: Also lints for non root modules

[rustbot]

r? @blyxyas

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[blyxyas]

I was testing the master version of this lint with the following setup:

// main.rs ==================================
#![deny(clippy::items_after_test_module)]

mod other_mod;
use crate::other_mod::add;

fn main() {
    println!("{}", add(3, 54));
}

// other_mod.rs ==============================
pub fn add(a: usize, b: usize) -> usize {
    a + b
}

#[cfg(test)]
mod tests {
    #[test]
    fn my_test() {}
}

const MY_ITEM: usize = 0;

But it doesn't emit. Turns out that the lint doesn't emit on any module that isn't on the main.rs / lib.rs. This is a bug.

[Alexendoo]

Reworked the lint to cover that, also added a hidden suggestion that can be applied by --fix and tweaked the spans while I was at it

[blyxyas]

Just some mini-nits and a question and this should be ready (｡･ω･｡)

[blyxyas]

Kinda weird how what should be submodule.rs's standard error is actually stored in in_submodule.stderr

[Alexendoo]

It's because it's the stderr output from running the in_submodule.rs test

[blyxyas]

LGTM, Thanks! ❤️ ( =ノωヽ=)

[blyxyas]

@bors r+

[bors]

📌 Commit dcc4001 has been approved by blyxyas

It is now in the queue for this repository.

[bors]

⌛ Testing commit dcc4001 with merge 279127c...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: blyxyas
Pushing 279127c to master...