dtolnay/iota

Support underscore constants

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#3 opened on Dec 26, 2019

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help wanted

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Description

As introduced in rust 1.37: https://blog.rust-lang.org/2019/08/15/Rust-1.37.0.html#using-unnamed-const-items-for-macros

Iota currently rejects code containing underscore names.

iota! {
    const A: u8 = 1 << iota;
        | _
        | C
}

error: no rules expected the token `|`
 --> src/main.rs:5:9
  |
5 |         | _
  |         ^ no rules expected this token in macro call

Contributor guide

Research direction
Examine the iota macro implementation to understand how it parses constant names, then modify the parser to accept underscore prefixed identifiers (e.g., ` `, ` A`) as valid constant names.
Tech stack
rust
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RustRust macros
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65