Empty iterator error

[obeis]

Closes #100635

[rust-highfive]

r? @fee1-dead

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[fee1-dead]

Thank you very much for the contribution! Could you please write this as a lint? (See rustc-dev-guide) You could also take a look at how clippy implemented this.

[fee1-dead]

I'm available on Zulip if you need any help.

[WaffleLapkin]

If done as a late lint I think this could also evaluate constants, for example

const A: u32 = 10;
const B: u32 = 0;

fn main() {
    for i in A..B {
        println!("{i}");
    }
}

[fee1-dead]

@rustbot author marking as waiting on author to address comments.

[rustbot]

rustc_error_messages was changed

cc @davidtwco, @compiler-errors, @JohnTitor, @estebank, @TaKO8Ki

[obeis]

@rustbot ready

[fee1-dead]

@rustbot author

[camsteffen]

This is a lint with a lot of room for enhancement. Static value range analysis could be used to reveal empty ranges x..y. Also there are ways other than for-loops to misuse an empty range (e.g. (2..1).map(|x| ..)). So that makes me wonder if this is really a good candidate for a rustc lint rather than space for 3rd party tools to explore.

[fee1-dead]

I was also wondering about this. Clippy has the lint.

However I think it would be nice to just add the for _ in 10..0 part and retain the other additional checks in clippy.

@rust-lang/compiler opinions?

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[bors]

☔ The latest upstream changes (presumably #102652) made this pull request unmergeable. Please resolve the merge conflicts.

[aDotInTheVoid]

@rustbot modify labels: -A-rustdoc-json

[apiraino]

Visiting again in T-compiler meeting on Zulip (notes). The general comment is that this lint should probably live in clippy in the first place rather than being implemented in the compiler.

@rustbot label -S-waiting-on-team

[bors]

☔ The latest upstream changes (presumably #104809) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC]

@obeis any updates on this?

[fee1-dead]

Closing as this should live in clippy for now.