Overflowing literal lint is silenced in range literals in loops on nightly

[varkor]

fn main() {
    for _ in 0..256u8 {} // should warn
}

since #60330.

[varkor]

It is hitting the err.emit() here:

rust/src/librustc_lint/types.rs

Line 102 in 9b67bd4

err.emit();

So I'm not quite sure why the error isn't being emitted yet.

[ehuss]

It appears to be hitting this line of code which is cancelling the diagnostic:

rust/src/librustc/lint/mod.rs

Line 746 in d15fc17

err.cancel()

[pnkfelix]

this appears to be a stable-to-beta regression (playpen)

[pnkfelix]

triage: P-high. Assigning to self.

[estebank]

We need to change

rust/src/librustc/lint/mod.rs

Line 871 in d15fc17

ExpnFormat::CompilerDesugaring(_) => return true, // well, it's "external"

to not consider desugarings coming from for loops as external. If that has regressions in our test suite, then we can add a new desugaring kind to differentiate between different parts of the for loop desugaring and target it further, but I do not expect that to be needed.

[varkor]

@pnkfelix: I've opened #61098 with a fix, based on @estebank's comment.