"left behind trailing whitespace" with comment between `let x =` and value

[camelid]

Code

Playground

fn main() {
    let number = 
    // A comment
    1;
}

Error

error[internal]: left behind trailing whitespace
 --> /playground/src/main.rs:2:2:17
  |
2 |     let number = 
  |                 ^
  |

warning: rustfmt has failed to format. See previous 1 errors.

Version

1.4.37-nightly (2021-10-05 25ec827) (current version on the playground)

[lesurp]

Not sure if that's the same root cause, but I got the same error with:

impl Bar {
    fn foo() {
        if let Some(curr_m) = m {
            for meow in baz {
                match &a.mission {
                    Some(m) => {
                        if 1 == 2 {
                            debug!(
                                "{}{}{}{}aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
                                a, a, a, a, 
                            );
                        }
                    }
                    None => {}
                }
            }
        }
    }
}

⮞ rustfmt paf.rs   
error[internal]: left behind trailing whitespace
  --> paf.rs:10:10:44
   |
10 |                                 a, a, a, a, 
   |                                            ^
   |

warning: rustfmt has failed to format. See previous 1 errors.

[camelid]

@lesurp I'd suggest opening another issue for that one since it seems like it might have a different cause.

[calebcartwright]

This has already been fixed in sourced (at some point) but was done on a different branch and needs to be pulled back into the mainline

[yuribudilov]

Hello,

I am running the latest Rust 1.57 (stable) and VS Code latest version (1.63.2) with latest (nightly) rust-analyser.

rustfmt 1.4.37-stable (f1edd042 2021-11-29)

I am still getting this error.
This prevents rust-analyzer VS Code formatting the Rust code, due to trailing spaces causing internal error.
It is not a big deal to manually fix the issue for those who know about this problem.
But it will trip the new Rust & VS-Code converts.

When will this fix be released to stable tool-chain?
Thank you.

[poliorcetics]

Same here, still present in rustfmt:

$ rustfmt +nightly -V
rustfmt 1.4.38-nightly (5d8767cb 2022-02-12)

[calebcartwright]

As noted above, this should just be a backport/cherry-pick.

I'm unlikely to be able to get to this any time soon, so for anyone looking for a faster resolution and/or simply willing to help, I'd suggest seeing if cherry-picking the commits from #3857 and/or #4550 resolves the issue (note those commits should be somewhere on the rustfmt-2.0.0-rc.2 branch, and they could be predicated on other changes that don't exist on our mainline master branch).

If the fix isn't in one of those, then you'll want to look through the other 100+ potential PRs listed in https://github.com/rust-lang/rustfmt/pulls?q=is%3Apr+label%3Abackport-triage+is%3Aclosed

[calebcartwright]

Also, please remember that the "left behind trailing whitespace" error message is a common symptom for a class of very different problems. It simply means that there was some construct in your input source code which rustfmt was unable to format for one reason or another, and in your original input you had trailing whitespace. If your original input is not the same type of construct, as represented at the AST level, then it's not the same issue; just the same symptom.

So while I appreciate folks commenting on an open issue to avoid duplicates, if you're not referring to a comment between the operator and the start of the right-hand-side in an assignment, then you're talking about something different than what's been reported in this issue.