rust-lang / rust-lang/rustfmt

`use_try_shorthand = true` disallows formatting on chains with comments

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A-call-chains A-comments C-bug only-with-option SO-use_try_shorthand
Dominant language
Rust
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Description

rustfmt.toml

# rustfmt.toml
# outdated default — `?` was unstable at the time
# additionally the `try!` macro is deprecated now
use_try_shorthand =true

main.rs

fn main() {
    let e: Result<(), &str> = Ok(());
    let _e = e // hello comment
            .map_err(|_| "This is an error message") // Hello comment - Fails to format
        .map(|_| ());

    println!("Hello, world!");
}
rustfmt version: 
    `rustfmt 1.7.0-stable (07dca489 2024-02-04)`
Nightly:
    `rustfmt 1.7.0-nightly (1388d7a0 2024-03-20)`

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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

Reproduce the formatting failure using the shown rustfmt.toml and main.rs, with use_try_shorthand = true and comments in the method chain. Start by tracing rustfmt's handling of try shorthand and commented chains, then add regression coverage for this example. Done means the chain formats successfully without dropping or misplacing either comment.

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
Active
Clarity
Clearly specified
Newbie friendliness
68/100

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