Suggest `..=` when someone tries to create an overflowing range

[D4v1d-L4u]

I tried this code:

for i in 0..256 as u8 {
        println!("{}", i);
}

I expected to see this happen:
printing all numbers from 0 to 255 (inclusive)

Instead, this happened:

error: literal out of range for `u8`
  --> src/main.rs:10:17
   |
10 |     for i in 0..256 as u8 {
   |                 ^^^
   |
   = note: the literal `256` does not fit into the type `u8` whose range is `0..=255`
   = note: `#[deny(overflowing_literals)]` on by default

rustc --version --verbose:

rustc 1.68.0 (2c8cc3432 2023-03-06)
binary: rustc
commit-hash: 2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74
commit-date: 2023-03-06
host: x86_64-unknown-linux-gnu
release: 1.68.0
LLVM version: 15.0.6

[Noratrieb]

The error is correct, 256 is indeed out of range for u8. You need to use 0..=255.

[scottmcm]

You can run that code if you want, by allowing the lint: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1d23a2e2a27104c5b6cb6351d5ad6722

But if you do you'll see that it will print nothing because the 256 overflows and becomes 0, so it's in 0..0 which is empty.

Examples like this where allowing the literal overflow would do something you don't want are exactly why this lint is deny-by-default 🙂

[scottmcm]

I've renamed this issue because the lint is correct. If there's anything to be done here, it would be to add a range-specific suggestion for this situation to help guide towards the correct code.

[mu001999]

@rustbot claim