Nested matches format into something invalid

[Smaug123]

Issue created from fantomas-online

Code

let u = ""
match
    match u with
    | null -> ""
    | s -> s
    with
    | "" -> x
    | _ -> failwith ""

Result

let u = ""

match match u with
      | null -> ""
      | s -> s with
| "" -> x
| _ -> failwith ""

Problem description

This is absolutely hilarious, and I am going to change our code here because the pattern is absurd. But it is a bug in Fantomas, so I'll raise it; Fantomas shouldn't produce invalid F# even if the input F# was this mad.

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 01/27/2021 07:36:19 - 138146e

Default Fantomas configuration

_{Did you know that you can ignore files when formatting from fantomas-tool or the FAKE targets by using a .fantomasignore file?}

[nojaf]

Hey Patrick, it was right of you to raise this.
I do feel like the fix for this might be a good old wrap it with parenthesis 😅.