Tracking issue for `illegal_floating_point_literal_pattern` compatibility lint

[est31]

This is a tracking issue for the compatibility lint disallowing floating point literals in patterns.

The corresponding RFC is RFC 1445. Originally, #36890 was the only tracking issue for floats in patterns, but after it was found out that the implementation of that lint doesn't cover literals (issue #41255), another lint and tracking issue were required.

The goal of this lint is to make code like this a hard error:

fn main() {
    let x = 13.4;

    match x {
        1.0 => println!("one"),
        22.4 => println!("two"),
        3.67 => println!("three"),
        13.4 => println!("thirteen point four"),
        _ => println!("anything"),
    }
}

• PR Implement the illegal_floating_point_literal_pattern compat lint #41293 introduces the lint as warn by default
• PR xxxx makes the lint deny by default
• PR xxxx makes the lint a hard error

[SimonSapin]

RFC 1445 is about const constants. Why are float literals restricted as well?

[SimonSapin]

This is a breaking change (rejecting previously-accepted programs) but as far as I can tell this one is not part of an accepted RFC.

[SimonSapin]

Is this a duplicate of #36890?

[est31]

RFC 1445 is about const constants. Why are float literals restricted as well?

Hmm a quick glance over the RFC seemed to confirm this. Let's discuss this in #36890, okay?

Is this a duplicate of #36890?

No, its separate. There are two separate lints. This one is about literals, the one tracked in that issue is about constants. I have opened the PR #41293 after finding out about #41255.

[withoutboats]

RFC 1445 is about const constants. Why are float literals restricted as well?

From my perspective, primitive literals (as opposed to destructuring struct literals) are a kind of constant. The same questions raised by consts in that RFC are raised by primitive literals.

[SimonSapin]

No, its separate. There are two separate lints. This one is about literals, the one tracked in that issue is about constants.

Yet the example given in #36890 uses literals.

From my perspective, primitive literals (as opposed to destructuring struct literals) are a kind of constant.

Given that we have a language keyword named const, I think it is reasonable to assume that constants are cont items and nothing else. If a different definition of the term is intended, it should absolutely be defined explicitly. This is not the case in this RFC.

[est31]

No, its separate. There are two separate lints. This one is about literals, the one tracked in that issue is about constants.

Yet the example given in #36890 uses literals.

The example quoted in the tracking issue you linked never was implemented that way. I have asked about whether to create a separate lint or add the check to the existing one, and it was decided to create a separate lint.

I guess the example should be removed from that issue's description.