Add lint almost_complete_digit_range

[phtown]

changelog: [almost_complete_digit_range]: Add digit analog to almost_complete_letter_range

I have added a lint that will detect '0'..'9' and suggest converting it to '0'..='9', the same way almost_complete_letter_range does for ascii letters. I tied into the implementation of AlmostCompleteLetterRange in order to do that, but I didn't change its interface.
This is my first contribution to Clippy, so please let me know if there's anything I should do differently. I'll be happy to incorporate any suggestions you have.
Thanks!

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Jarcho (or someone else) soon.

Please see the contribution instructions for more information.

[Jarcho]

Just a comment on naming. It would be better to rename almost_complete_letter_range to almost_complete_range, and then use the same lint to implement both. Changes look good otherwise.

Might be easier to start from master, use cargo dev rename_lint almost_complete_letter_range almost_complete_range and then add your changes onto that.

[phtown]

While making the change you suggested I ran into an issue I hope you can shed some light on. If you run the test tests/ui/almost_complete_range and look at the macro b, you'll see the lint only triggers on the first instance it should. Is that expected behavior for macro_rules macros? I can't see anything in the lint definition that would make it do that.

[Jarcho]

I'm surprised the compiler isn't complaining about that. Only the first arm of that macro will ever be expanded.

You probably meant to do something like

macro_rules! b {
    () => {{
        let _ = 'a'..'z';
        let _ = 'A'..'Z';
        let _ = '0'..'9';
    }};
}

[phtown]

Oh, woops. Looks like rustc and I are equally good at noticing when a macro definition is wrong.

[Jarcho]

Looks good to go. You can squash the changes. Probably best to have the rename as a separate commit, but not necessary if that's too much effort.

[Jarcho]

Weird. I wonder what you did.

Thank you. @bors r+

[bors]

📌 Commit 4c80f21 has been approved by Jarcho

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4c80f21 with merge ef2018c...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Jarcho
Pushing ef2018c to master...