Implicit unit else results in extra lines with each reformat

[renngar]

Issue created from fantomas-online

Code

let fn () =
    if true then
        DoSomething ()
        DoSomethingElse()
    elif shouldWe then
        Whatever()

let  nextfunc () =
    printf "Hi"

Result

let fn () =
    if true then
        DoSomething()
        DoSomethingElse()
    elif shouldWe then
        Whatever()


let nextfunc () = printf "Hi"

Problem description

Nested ifs or if-else chains can result in additional blank lines being inserted with each reformat. This seems to happen only when they have an implicit unit-returning else tail.

I have many variants of this in my code. Some occur at the end of a function others in the middle of a function. In the latter case, the rest of the function is pushed further down the page with each iteration. In the former, the same happens to the following function.

Extra information

• The formatted result breaks by code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.

I am not familiar with the Fantomas code, but would be will to try to fix this with some pointers or hints.

In places I've had to resort to things like:

let private setState (host: IViewHost) retryMsg program (state: Model) dispatch =
    // create new view and update the host only if new model is not equal to a prev one
    let stateDiffers = (Some state).Equals(!stateRef) |> not

    if stateDiffers then
        let updated = state.ThrottleUpdates() |> not
        // Only build a new view if the screen has been updated with the previous one
        if updated then
            stateRef := Some state
            let view = ((Program.view program) state dispatch)
            host.Update(Some(view :> IView))
        elif retryMsgInFlight |> not then
            // Otherwise, dispatch a message after a while so that we can retry updating with the latest.
            DispatcherTimer.RunOnce(Action(fun () -> retryMsg |> dispatch), TimeSpan.FromMilliseconds 50.0)
            |> ignore

            retryMsgInFlight <- true
        else
            () // Avoid Fantomas formatting problems
    else
        () // Avoid Fantomas formatting problems

Interestingly, if I only put the comment on one of the elses, Fantomas will insert it on both.

Options

Fantomas Master at 10/02/2020 17:06:53 - 31305c2

Default Fantomas configuration

[nojaf]

Hello @renngar, thanks for reporting this.
I believe we are adding a newline too much somewhere in CodePrinter.
Sorry that this doesn't really narrow this down a lot.

The learn about how Fantomas works internally, you can check out some videos on YouTube.
And check out our little Contributing guide section.

As for tackling this, I propose you create a unit test in IfThenElseTests.fs and do some debugging to see which code path is taken.

Don't hesitate to open a draft PR and ask some further questions down the road.