`use_try_shorthand = true` disallows formatting on chains with comments

[Laifsyn]

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# outdated default — `?` was unstable at the time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)`

[jieyouxu]

Triage:

• Default stable config with rustfmt --check formats
• rustfmt --check --config=use_try_shorthand=true as reported does not format the chain.
  • The trailing // Hello comment - Fails to format comment is load-bearing.

[ytmimi]

@jieyouxu is use_try_shorthand=true necessary to trigger this? I don't see any try!() calls in the input snippet.

[jieyouxu]

Is use_try_shorthand=true necessary to trigger this? I don't see any try!() calls in the input snippet.

From my testing, apparently that is indeed necessary¹ to trigger this (at least with default stable option-values, i.e. just --check, I don't observe this failed formatting). The lack of try!() doesn't seem to actually matter curiously.

Footnotes

1. But not sufficient, the trailing // Hello comment seems to be additionally needed as a "sufficient" condition to trigger this ↩

[matthewhughes934]

I think I accidentally fixed this while doing some reworking of the chain code: see #7095

I was noticed some other bugs with use_try_shorthand and came looking to see if they were already documented. Then tried reproducing this bug on my branch, and it wasn't working 😅 , then got very confused trying to bisect master to see which commit fixed it.