rustfmt takes 32 seconds for this 1140 character file

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") }) }) }) }) }) }) }) }) }) }) });
                    }
                }
            }
        }
    }
}

Start by reproducing the reported timing with the 1140-character nested-module example, then compare it with the version where one module layer is removed. Investigate the rustfmt path exercised by this input; done means the example no longer takes about 32 seconds to format and the regression is covered by an appropriate test.