Strange bug with `cargo fmt`

help
1

Hi! I've been having some strange issues with rust's formatter recently, specifically in one file. When I add an extra line, I get an error "left behind trailing whitespace." However, it still won't format the code when I remove that line. When I remove lines 27-173 it starts formatting correctly. The code compiles just fine as well.

2

I suspect it would be helpful to post the exact error message.

3

The strangest thing is there aren't any messages, that's what really got my head scratching.

On further investigation, I've also reproduced it by copying the code in the file into a new rust project, no fmt settings. When removing those lines, it formats the code.

To reproduce:

cargo new bugtest
cd bugtest

Replace contents of main.rs with contents of m_0000_add_polyphonic_prop.rs:

cargo fmt --all

No errors, no formatting.

Remove lines 26-181. Now it formats.

4

Oops, I should also post system info:

cargo fmt --version
# rustfmt 1.5.1-stable
uname -r
# 6.0.9-arch1-1
5

I've been able to reduce it to this, I'll keep hacking away to see if I can get a smaller example though:

pub fn main() {
    let foo: Vec<()> = vec![];

    foo
        .iter()
        .for_each(|_| {
                            let x = "a really really really really really really really really really long line of text";
        });
}
6

It will reformat correctly inside of a normal block, but when it's in a closure block it stops formatting.

7

Never mind, looks like it's an open issue: Gives up on chains if any line is too long. · Issue #3863 · rust-lang/rustfmt · GitHub

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