rust-lang / rust-lang/reference
Clarify longest match behavior of the grammar
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- Dominant language
- Rust
- Stars
- 1.6k
- Forks
- 607
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Description
https://doc.rust-lang.org/reference/expressions.html claims as binds tighter than than + or <
Indeed, with +: let b = 0 as u32 + 0 as u32 parses correctly,
However, with <: let b = 0 as u32 < 0 as u32 gives a syntax error.
I suspect this is due to a conflict in the grammar that looks ahead at the token < and sees the beginning of a type application (in types), but if I'm reading just https://doc.rust-lang.org/reference/expressions.html#r-expr.precedence there's not enough information for me to write a correct Rust syntax printer.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the Rust Reference expressions page, especially the precedence section linked in the issue, and compare the + and < examples. Trace the grammar wording relevant to the lookahead for <; done means the Reference clearly explains the longest-match behavior and provides enough guidance for a correct Rust syntax printer.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100