Can we stop rustc --test warning of an unused main()?

[chris-morgan]

$ echo 'fn main(){}' | rustc --test -
<anon>:1:1: 1:12 warning: code is never used: `main`, #[warn(dead_code)] on by default
<anon>:1 fn main(){}
         ^~~~~~~~~~~

I have put #[cfg(not(test))] on main a couple of times (though perhaps #[allow(dead_code)] would be better) and I have just observed another person doing it. Would it be reasonable to make the dead code lint permit main to be unused?

Perhaps it would be better to disable all warnings by default in test mode. Some people use tests as a "poor man's REPL", and warnings are just noise there.

[huonw]

The dead_code lint is really helpful for indicating tests that are missing their #[test] (and also the lints are useful for generally making sure that the tests do what they're supposed to).

[nixpulvis]

👍 for ignoring unused main. I agree keeping other dead code warning is defiantly a good idea, but warning about main is just noise.

[doy]

+1 to specifically ignoring main, but keeping other warnings.

[nixpulvis]

On a related note, ignoring main seems to ignore things when compiled with --test when trying to circumvent this issue.

[brycefisher]

:+ for ignoring main

[steveklabnik]

I'm interested in sheparding a patch like this, if anyone wants to give it a shot.

[Siosm]

@steveklabnik I've made a first try to fix this. This tentative fix is not valid but I already got failed tests that I'm investigating.
I think that I need to find a way to get the attributes associated with a function to check if it as the 'start' or 'main' attribute. The current documentation is unclear on this specific point (see http://doc.rust-lang.org/reference.html#function-only-attributes and http://doc.rust-lang.org/reference.html#marker-types).
Also, are functions starting with a '_' internal only? (src/librustc/middle/dead.rs:521)

[steveklabnik]

Starting with a _ is intended to supress warnings, yeah

[huonw]

@Siosm, NB. it is purely a warning/conventions thing, it just controls the lints, it doesn't have any effect on what is accessible externally or anything like that (that's the pub keyword).

[Siosm]

@huonw Ok. Is this documented somewhere? So far I can not find any mention of it in the reference or in the guide.

[felixc]

This issue appears to also affect the Emacs Flycheck mode for Rust. Emacs users will get Flycheck warnings saying main() is dead code. Arguably it's a bug in their end (is it?), but it's another data point to suggest it's unexpected behaviour.