Lint for functions that don't return but aren't written as "-> !"

[jruderman]

I think this should warn: f never returns, but it claims to return int.

fn f() -> int {
  fail!("f")
}

fn main() {
  f();
}

[sfackler]

It's a decently common idiom to stub out something with things like

fn foo() -> Bar {
    unimplemented!();
}

[thestinger]

@sfackler: It makes sense for the compiler to warn about a stubbed out function. It's a reminder that you should fix it before making a release.

[kmcallister]

Trait impls should be exempted, though, since their types are imposed externally.

[nham]

Triage: still an issue (rustc 1.1.0-nightly (4b88e8f63 2015-05-11) (built 2015-05-12))

FYI the updated code is:

fn f() -> isize {
  panic!("f")
}

fn main() {
  f();
}

[ghost]

@Manishearth does clippy offer this?

[Manishearth]

@Toby-s No, but file a bug. Given that there are some common patterns that encourage this, I'd prefer it to be a pedantic lint (off by default)

[steveklabnik]

Since new lints have a big impact on users of rustc, the policy is that they should go through the RFC process like other user-facing changes. As such, I'm going to give this one a close, but if anyone comes across this ticket and wants this lint, consider adding it to clippy and/or writing up an RFC. Thanks!