request for an option for not shrink into one line

Currently rust fmt wrap the lines into single line if max_width is large enough. However
I sometimes intendedly use next line to make types more visible to me. I would like to see
if there is any options to disable things shrinking into one line. If it is a no please kindly
close this issue, thanks.

Input

pub async fn update_config(
    cfg: HashMap<String, HashMap<String, f64>>,
) -> Result<(), Box<dyn Error>> {
    Ok(())
}

Output

pub async fn update_config(cfg: HashMap<String, HashMap<String, f64>>) -> Result<(), Box<dyn Error>> {
    Ok(())
}

Expected output

pub async fn update_config(
    cfg: HashMap<String, HashMap<String, f64>>,
) -> Result<(), Box<dyn Error>> {
    Ok(())
}

Meta

• rustfmt version: 1.4.20-nightly (48f6c32 2020-08-09)
• From where did you install rustfmt?: cargo install fmt sth like that