Chained method statements are not formatted if they contain a string that exceeds `max_width`

[J-Westin]

The following example does not get formatted at all when running cargo fmt, and does not report anything on cargo fmt --check. I've set max_width = 50 to make it easier to visualize, but similar behavior can be seen with the default max width.

// max width of 50 characters is here ---------->|
fn _finagle() {
    let _my_string =
        "The quick brown fox jumps over the lazy dog."


             .split(" ")
  .next()

            .unwrap();
}

This seems to be triggered by the fact that the string literal cannot be formatted to fit within max_width, which can be demonstrated by shortening it. Removing "lazy" causes the above example to get formatted to this:

// max width of 50 characters is here ---------->|
fn _finagle() {
    let _my_string =
        "The quick brown fox jumps over the dog."
            .split(" ")
            .next()
            .unwrap();
}

However, I would have expected the original example to format to this:

// max width of 50 characters is here ---------->|
fn _finagle() {
    let _my_string =
        "The quick brown fox jumps over the lazy dog."
            .split(" ")
            .next()
            .unwrap();
}

It seems strange for the formatter to give up on the entire statement and ignore random blank lines and indentation if part of it can't be fit within the line length limit.

I'm using rustfmt 1.8.0-stable (05f9846f89 2025-03-31) with edition = "2024".

[sjmik]

I wonder if I have the same issue, or if this is different... I'll just piggyback on your issue instead of creating a new one.

This code breaks the formatter for the entire file, not just the one statement:

use clap::{command, Arg};
pub fn main() {
    command!()
       
        .arg(
            Arg::new("ignore-case")         
                        .long("ignore-ca")
                .value_name("FILE")
                .help("________10________20________30________40________50________60________70________80__")
        );
}

Now, if I delete one of the letters from ANY of the strings, it will format. For example, let's delete E from FILE and run the formatter:

use clap::{command, Arg};
pub fn main() {
    command!().arg(
        Arg::new("igore-case")
            .long("ignore-ca")
            .value_name("FIL")
            .help(
            "________10________20________30________40________50________60________70________80__",
        ),
    );
}

This happened with every version I tried.

$ rustup run nightly rustfmt -v src/main.rs 
Formatting /work/scratch/src/main.rs
Spent 0.001 secs in the parsing phase, and 0.000 secs in the formatting phase
error[internal]: left behind trailing whitespace
 --> /work/scratch/src/main.rs:5:5:1
  |
5 |        
  | ^^^^^^^
  |

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

$ rustup run nightly rustfmt -V
rustfmt 1.8.0-nightly (59aa1e8730 2025-06-03)
$ rustup run 1.87.0 rustfmt -V
rustfmt 1.8.0-stable (17067e9ac6 2025-05-09)
$ rustfmt -V
rustfmt 1.8.0-stable (9fc6b43126 2025-01-07)

All of my settings are default, no rustfmt.toml, etc.
Here is the Cargo.toml for the test:

[package]
name = "scratch"
version = "0.1.0"
edition = "2021"

[dependencies]
clap = { version = "4.5.39", features = ["cargo"] }

[sjmik]

@ytmimi, do you think my issue really is the same as #3863?

Two things seem different:

• rustfmt obviously can fit the long string into 97 characters
• nothing else in my file gets formatted when the issue is present, the entire formatter is broken

[ytmimi]

@sjmik I'd suggest opening up a new issue for what you're experiencing. The original issue is certainly a duplicate.