skip exit late lint pass on tests

[Jared-Prime]

changelog: [exit]: When using the --test or --all-targets flag, the exit lint should not fail on the main function.

Fixes #13518

With help from @sesgoe

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[y21]

This suppresses the lint entirely in --test sessions and will not emit a lint anywhere in the crate, even if we aren't actually in a main fn and we should emit a warning, right?

I think that would interact confusingly with #[expect] and create a situation similar to #13358, where if you have something like:

fn foo() {
  #[expect(clippy::exit)]
  std::process::exit();
}

and run cargo clippy --all-targets, then you get an unfulfilled lint expectation, but if you remove the #[expect], you do get the warning there.

--all-targets runs clippy twice, once without --test and again with --test, so only sometimes emitting a warning dependent on the session (like is done here) is a bit confusing for users IMO

[y21]

I wonder if, instead of using !is_entrypoint_fn at the end of the condition chain, which I guess is also dependent on the session and different for the test harness, we could just change that to check if the enclosing function's name is not literally "main". That seems closer to what we actually want and would be more consistent between compiler sessions

[sesgoe]

@y21 I had the same thought after reading your first comment, and upon consideration, this seems like a good way to go

I saw the if cx.sess().is_test_crate() { return; } pattern elsewhere, which is why it seemed reasonable to slot it in here too -- the only real thought was: in a test context, is this lint relevant?

The confusing interaction with --all-targets is worth fixing, and checking that the name is literally main makes it clear in both compilation contexts/sessions, so that feels like a good solution.

[Jared-Prime]

Thanks, @y21 . I added the changes and documentation updates recommended by @sesgoe then removed the blanket skip for test crates. Let me know if anything else required here!