rustfmt takes 32 seconds for this 1140 character file

[Volker-Weissmann]

Formatting the code below takes 32 seconds on my machine.
This is not bad performance, this is a bug (If I remove one mod layer it takes 0.2 seconds).

In my real world, program (that uses pest), running cargo expand is therefore nearly impossible (I stopped it after an hour)

mod modA {
    mod modB {
        mod modC {
            mod modD {
                mod modE {
                    fn func() {
                        state . rule (Rule :: myrule , | state | { state . sequence (| state | { state . sequence (| state | { state . match_string ("abc") . and_then (| state | { super :: hidden :: skip (state) }) . and_then (| state | { state . match_string ("def") }) }) . and_then (| state | { super :: hidden :: skip (state) }) . and_then (| state | { state . sequence (| state | { state . optional (| state | { state . sequence (| state | { state . match_string ("abc") . and_then (| state | { super :: hidden :: skip (state) }) . and_then (| state | { state . match_string ("def") }) }) . and_then (| state | { state . repeat (| state | { state . sequence (| state | { super :: hidden :: skip (state) . and_then (| state | { state . sequence (| state | { state . match_string ("abc") . and_then (| state | { super :: hidden :: skip (state) }) . and_then (| state | { state . match_string ("def") }) }) }) }) }) }) }) }) }) }) });
                    }
                }
            }
        }
    }
}

[ytmimi]

Reopen since we had to revert #5139 in #5403