rust-lang / rust-lang/rustfmt

Formatting a line comment inbetween a function parameter and its type results in the type being commented out

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A-comments C-bug I-invalid-code
Dominant language
Rust
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Description

Formatting

fn foo(x: //comment here
u32) {} 

results in (on playground 1.8.0-nightly (2025-03-22 b48576b4db))

pub fn foo(x: //comment here u32
) {
}

I agree this is a remarkably weird place to put a comment, but it should at least not result in breaking compilation.

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Research direction

Reproduce the reported formatting with the Rust snippet on rustfmt or the referenced Rust Playground version. Trace how the formatter handles a line comment between a parameter and its type, then verify that formatting preserves compilable code and does not comment out the type.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
50/100

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