Error when combining #if directive with async block and let

[theimowski]

Issue created from fantomas-ui

Fantomas fails to format if given a conditional #if block in conjunction with async block and a let binding within (works ok when I remove let from async)

Code

#if TEST
let f () =
    async {
        let x = 2
        return x
    }
#endif

Error

Exception: Fantomas is trying to format the input multiple times due to the detect of multiple defines.
There is a problem with merging all the code back togheter. Please raise an issue at https://github.com/fsprojects/fantomas/issues. Stack Trace:    at Microsoft.FSharp.Core.PrintfModule.PrintFormatToStringThenFail@1637.Invoke(String message) in E:\A\_work\130\s\src\fsharp\FSharp.Core\printf.fs:line 1637
   at Fantomas.String.merge(String a, String b)
   at Fantomas.CodeFormatterImpl.merged@415.Invoke(String a, String b)
   at Microsoft.FSharp.Collections.ListModule.Fold[T,TState](FSharpFunc`2 folder, TState state, FSharpList`1 list) in E:\A\_work\130\s\src\fsharp\FSharp.Core\list.fs:line 221
   at Microsoft.FSharp.Collections.ListModule.Reduce[T](FSharpFunc`2 reduction, FSharpList`1 list) in E:\A\_work\130\s\src\fsharp\FSharp.Core\list.fs:line 233
   at Fantomas.CodeFormatterImpl.format@405-1.Invoke(Tuple`2[] _arg1)
   at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvokeNoHijackCheck[a,b](AsyncActivation`1 ctxt, FSharpFunc`2 userCode, b result1) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 416
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 109
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.FSharp.Control.AsyncResult`1.Commit() in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 349
   at Microsoft.FSharp.Control.AsyncPrimitives.RunSynchronouslyInCurrentThread[a](CancellationToken cancellationToken, FSharpAsync`1 computation) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 870
   at Microsoft.FSharp.Control.AsyncPrimitives.RunSynchronously[T](CancellationToken cancellationToken, FSharpAsync`1 computation, FSharpOption`1 timeout) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 890
   at Microsoft.FSharp.Control.FSharpAsync.RunSynchronously[T](FSharpAsync`1 computation, FSharpOption`1 timeout, FSharpOption`1 cancellationToken) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 1153
   at Server.Result.attempt[a](FSharpFunc`2 f) in /build/src/Server/Server.fs:line 24

Options

Fantomas 3.0.0

Name	Value
IndentOnTryWith	false
IndentSpaceNum	4
KeepNewlineAfter	false
PageWidth	120
ReorderOpenDeclaration	false
SemicolonAtEndOfLine	false
SpaceAfterComma	true
SpaceAfterSemicolon	true
SpaceAroundDelimiter	true
SpaceBeforeArgument	true
SpaceBeforeColon	false
StrictMode	false

[nojaf]

I think the problem is more related to having only code within an #if directive.
Nevertheless thanks for reporting this bug.

[theimowski]

If you remove the let binding, it works perfectly fine