Rustfmt fails to fmt

[jyn514]

Consider the following code:

impl S {
    fn f() {
        self.g(
            {
                if b {
                    Err(w(
                        i(
                            "expected float or integer types for both operands of {}, got '{}' and '{}'",
                            token,
                        )), left)
                }
                match d {
                    _ => h(m,b), 
                }
            },
        )
    }
}

There are many style issues, but the one that caught my attention was the lack of a space after the comma. I tried and sure enough if you add a trailing space rustfmt will refuse to format at all and give an internal error as a result:

error[internal]: left behind trailing whitespace
  --> /home/joshua/src/rust/rcc/comma.rs:13:13:32
   |
13 |                     _ => h(m,b), 
   |                                 ^

[jyn514]

This appears to be related to the length of the string somehow, if I cut down the length it formats correctly:

impl S {
    fn f() {
        self.g(
            {
                if b {
                    Err(w(
                        i(
                            "expected ",
                            token,
                        )), left)
                }
                match d {
                    _ => h(m,b), 
                }
            },
        )
    }
}

transformed to

impl S {
    fn f() {
        self.g({
            if b {
                Err(w(i("expected ", token)), left)
            }
            match d {
                _ => h(m, b),
            }
        })
    }
}

[calebcartwright]

Closing in favor of #3863