Attribute on member of mutually dependent types fails to validate

[ntwilson]

Issue created from fantomas-online

Code

module BreakFantomas

open System.Diagnostics.CodeAnalysis

type X = A
and Y = B with
    [<ExcludeFromCodeCoverage>] 
    member this.M () = true

Result

module BreakFantomas

open System.Diagnostics.CodeAnalysis

type X = A

and Y = B
    with
        member [<ExcludeFromCodeCoverage>] this.M() = true

Problem description

It formats via the web page, but the output isn't valid F#, and it lists parse failures at the bottom. Via the CLI tool, it fails with

Formatted content is not valid F# code

If you change and Y = B to type Y = B everything works as expected.

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 4.6 branch at 10/15/2021 14:45:28 - d8896cc

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]

Hello, thank you for reporting this issue.
This feels related to #1898 and #1874.
I should check to be sure though.

I believe the problem is introduced by the ASTContext, the field IsFirstChild is used for the recursive type and has an unexpected impact on the attribute generation later on.
Are you interested in submitting a PR for this?