rust-lang / rust-lang/rustfmt

Comment in trait visibility position causes token duplication

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A-comments C-bug
Dominant language
Rust
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Description

Just noticed some weird behaviour, not sure if it's been reported already, I tried searching but I'm not sure how to classify it

this:

pub/* (crate) */ trait MyTrait {}

gets reformatted as:

pub trait MyTrait /* (crate) */ trait MyTrait {}

Test:

$ rustfmt <<< 'pub/* (crate) */ trait MyTrait {}'
pub trait MyTrait /* (crate) */ trait MyTrait {}

Worth noting, I didn't observe this behavior with structs, enums, unions and expanding the comment's scope to include the pub, it behaves correctly with this:

/* pub (crate) */ trait MyTrait {}

getting reformatted to:

/* pub (crate) */
trait MyTrait {}

Contributor guide

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the reported input with rustfmt and compare the trait case with the struct, enum, and union cases described in the issue. Trace the formatting path for a visibility comment and verify that the completed behavior preserves the comment without duplicating the trait declaration.

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
Mostly clear
Newbie friendliness
45/100

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