Problem Merging multiple compiler directives code

[Rajivhost]

Issue created from fantomas-online

Code

let Ok (content: string) =
#if API_GATEWAY || MADAPI
    APIGatewayHttpApiV2ProxyResponse(
        StatusCode = int HttpStatusCode.OK,
        Body = content,
    #if API_GATEWAY
        Headers = Map.empty.Add("Content-Type", "text/plain")
    #else
        Headers = Map.empty.Add("Content-Type", "application/json")
#endif
    )
#else
    ApplicationLoadBalancerResponse(
        StatusCode = int HttpStatusCode.OK,
        Body = content,
        Headers = Map.empty.Add("Content-Type", "text/plain")
    )
#endif

Problem description

We got this error:

System.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 together.
[API_GATEWAY, MADAPI] has 21 fragments
[] has 22 fragments
[API_GATEWAY] has 21 fragments
[MADAPI] has 20 fragments
Please raise an issue at https://fsprojects.github.io/fantomas-tools/#/fantomas/preview.
at Microsoft.FSharp.Core.PrintfModule.PrintFormatToStringThenFail@1439.Invoke(String message) in D:\a_work\1\s\src\fsharp\FSharp.Core\printf.fs:line 1439
at Fantomas.CodeFormatterImpl.format@410-3.Invoke(FSharpList1 _arg2) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodeFormatterImpl.fs:line 436 at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvokeNoHijackCheck[a,b](AsyncActivation1 ctxt, b result1, FSharpFunc2 userCode) in D:\a\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 465 at Fantomas.Async.map@167-2.Invoke(AsyncActivation1 ctxt) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Utils.fs:line 167
at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in D:\a_work\1\s\src\fsharp\FSharp.Core\async.fs:line 105

[nojaf]

Hello @Rajivhost, thank you for reporting this issue.

I was able to reproduce the problem using code comments.

This is a trivia issue, we don't print the comment (or in your case the #if) in

fantomas/src/Fantomas/CodePrinter.fs

Lines 2876 to 2880 in 896bc77

	let genExpr astContext e =
	match e with
	| InfixApp (equal, operatorExpr, e1, e2) when (equal = "=") ->
	genNamedArgumentExpr astContext operatorExpr e1 e2
	| _ -> genExpr astContext e

To do this, we would need to extend the InfixApp active pattern with the range of the outer SynExpr.App in

fantomas/src/Fantomas/SourceParser.fs

Lines 805 to 809 in 896bc77

	let (|InfixApp|_|) synExpr =
	match synExpr with
	| SynExpr.App (_, true, (Var "::" as e), Tuple ([ e1; e2 ], _), _) -> Some("::", e, e1, e2)
	| SynExpr.App (_, _, SynExpr.App (_, true, (Var s as e), e1, _), e2, _) -> Some(s, e, e1, e2)
	| _ -> None

Once this has been added, in CodePrinter you can to do something like:

     | InfixApp (equal, operatorExpr, e1, e2, range) when (equal = "=") -> 
         genNamedArgumentExpr astContext operatorExpr e1 e2 
         |> genTriviaFor SynExpr_App range

Are you interested in submitting a PR for this?