Wrong anon module formatting when filename starts with a digit

[auduchinok]

Consider file 60Seconds.fsx with following content:

let simplePatternMatch =
    let x = "a"
    match x with
    | "a" -> printfn "x is a"
    | "b" -> printfn "x is b"
    | _ -> printfn "x is %s" x

It's being formatted to

     |
     |
     |
module ``60Seconds``
let simplePatternMatch =
    let x = "a"
    match x with
    | "a" -> printfn "x is a"
    | "b" -> printfn "x is b"
    | _ -> printfn "x is %s" x

[nojaf]

Hmm, not getting this by formatting with command line.
Any idea how you are doing the formatting? What code do you call?

[auduchinok]

@nojaf Sorry I forgot to add the initial issue link.
https://youtrack.jetbrains.com/issue/RIDER-24086
I suppose it's default Rider formatting settings, i.e. have Preserve end of line option turned on.

[nojaf]

Ok, I'm able to reproduce this in Rider. I think there are two problems:

• A module statement is added where none existed.
• Preserve end of line adds pipes and messes up the code.

For the first problem I'd like to know how Fantomas is called when pressing Reformated Code.
@auduchinok could you point me to the code in https://github.com/JetBrains/fsharp-support?

As for the second problem, --preserve-eol will go away in the next major so I'm not that eager to solve that problem.

[auduchinok]

@nojaf Sure, look at ReformatCode.fs.

The first problem looks like a repro for #264.

As for the second problem and that option going away I'd be happy to discuss it when the next version is being designed as I think it's quite important to try to preserve user formatting for line endings and that's why we have this option turned on by default.

[nojaf]

Well as might know by now I'm not sure we should preserve user formatting.

• Other formatters (based on AST) don't have this. F.ex prettier.
• Fantomas didn't have this option for most of its existence. I feel like we merged it in without fully understanding all the consequences. And the current implementation has a lot of issues, even more than logged. And the original writer of --preserveEOL has moved on.
• preserve user formatting is also a very broad spectrum. Where do we draw the line?

Feel free to further discuss in #390.

[auduchinok]

Other formatters (based on AST) don't have this. F.ex prettier.

R# and IntelliJ do it for other languages. I believe as a user I'd expect it to do it for F# code as well. :)

Thanks, I'll try to add some meaningful input there.

[nojaf]

Is there any way of knowing the value of parsedInput ?
What would the exact AST be? Could you show me how the AST was created?

[auduchinok]

It's coming from FSharpChecker.ParseFile, called inside FSharpCheckerService.fs. It should be the same result as when using FSharp.Compiler.Sevice.dll from NuGet inside a script, at least before the recently (yesterday?) released FCS, due to changes in dotnet/fsharp#6027 which help with dealing with anon modules.
Otherwise, If you want to debug our code in Rider, you can build the F# plugin and attach to R# process calling everything discussed above.

[nojaf]

Yeah I knew it would have to come from FSharpChecker but was more wondering what FSharpParsingOptions are passed.

[auduchinok]

It's default options with file name set and IsExe = true for scripts (i.e. this case).

let getParsingOptionsForSingleFile (file: IPsiSourceFile) =
        { FSharpParsingOptions.Default with SourceFiles = [| file.GetLocation().FullPath |] }

member x.GetParsingOptions(file) =
    if isScriptLike file then { getParsingOptionsForSingleFile file with IsExe = true } else

    getOrCreateFSharpProject file
    |> Option.map (fun fsProject -> fsProject.ParsingOptions)
    |> Option.defaultWith (fun _ -> getParsingOptionsForSingleFile file)

[nojaf]

Ok, thanks for all the pointers. I can try and write a unit test now.

[nojaf]

I can't reproduce this anymore in Rider.
And I've added a regression test.
Should be ok, please re-open if needed.