Fantomas format is "unstable/oscillates" after upcast operator: adds/removes empty line

[kodfodrasz]

Issue created from fantomas-online

Code

module S3v2

open System.Threading.Tasks
open Amazon.Runtime

let waitAndUpcast (x: Task<'t>) =
    let t =
        x |> Async.AwaitTask |> Async.RunSynchronously
    x.Result :> AmazonWebServiceResponse

Result

module S3v2

open System.Threading.Tasks
open Amazon.Runtime

let waitAndUpcast (x: Task<'t>) =
    let t =
        x |> Async.AwaitTask |> Async.RunSynchronously

    x.Result :> AmazonWebServiceResponse

Problem description

After having run the formatter on the code above, an empty line was added before the x.Result :> AmazonWebServiceResponse line.
When the output is pasted to the input field the line will be removed.
Eventually re-running fantomas with the snippet above will oscillate between two state differing only in that empty line.

I have noticed this while running fantomas 4.2.0 locally in check mode on a file with the above snippet in it.

When the upcast operation (:> AmazonWebServiceResponse) is removed the code formatting is stable.

Please describe here the Fantomas problem you encountered.
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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.

Options

Fantomas Master at 11/02/2020 11:33:23 - f7b8f3a

Default Fantomas configuration