Parse Exception When Using Preprocessor Directives

[1eyewonder]

Issue created from fantomas-online

Code

#r "nuget: Expecto"

#if FABLE_COMPILER_PYTHON
open Fable.Pyxpecto
#endif
#if FABLE_COMPILER_JAVASCRIPT
open Fable.Mocha
#endif
#if !FABLE_COMPILER
open Expecto

[<Tests>] //needed for `dotnet test` to work
#endif
let allTests = testList "All Tests" [ ]

[<EntryPoint>]
let main argv =
#if FABLE_COMPILER_PYTHON
    Pyxpecto.runTests allTests
#endif
#if FABLE_COMPILER_JAVASCRIPT
    Mocha.runTests allTests
#endif
#if !FABLE_COMPILER
    Tests.runTestsWithCLIArgs [] argv allTests
#endif

Error

Fantomas.Core.ParseException: ParseException
  [{ Severity = Error
     SubCategory = "parse"
     Range = Some (26,0--26,6)
     ErrorNumber = Some 58
     Message =
      "Unexpected syntax or possible incorrect indentation: this token is offside of context started at position (17:1). Try indenting this further.
To continue using non-conforming indentation, pass the '--strict-indentation-' flag to the compiler, or set the language version to F# 7." };
   { Severity = Error
     SubCategory = "parse"
     Range = Some (26,0--26,6)
     ErrorNumber = Some 10
     Message =
      "Incomplete structured construct at or before this point in binding" }]
   at Fantomas.Core.CodeFormatterImpl.parse@39-6.Invoke(Unit unitVar) in /_//src/Fantomas.Core/CodeFormatterImpl.fs:line 47
   at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvoke[T,TResult](AsyncActivation`1 ctxt, TResult result1, FSharpFunc`2 part2) in D:\a\_work\1\s\src\FSharp.Core\async.fs:line 508
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in D:\a\_work\1\s\src\FSharp.Core\async.fs:line 112

Problem description

When working on a PR over in FsToolkit.ErrorHandling, I came across this parse exception. Here is the link to the actual code. We are currently working around this by utilizing the .fantomasignore file.

Extra information

• The formatted result breaks my code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.
• I would like a release if this problem is solved.

Options

Fantomas main branch at Dec 17, 2024

Default Fantomas configuration

_{Did you know that you can ignore files when formatting by using a .fantomasignore file?
PS: It's unlikely that someone else will solve your specific issue, as it's something that you have a personal stake in.}

[nojaf]

Hello, do all combinations of defines lead to valid code here?
If so, more information on what happens can be found in our docs.

Are you interested in submitting a PR for this?

[1eyewonder]

I see what you mean in regards to all paths needing to be correct i.e. the main function needs to have a return if none of the flags are true. Adding the one line allows fantomas to parse correctly.

#r "nuget: Expecto"

#if FABLE_COMPILER_PYTHON
open Fable.Pyxpecto
#endif
#if FABLE_COMPILER_JAVASCRIPT
open Fable.Mocha
#endif
#if !FABLE_COMPILER
open Expecto

[<Tests>] //needed for `dotnet test` to work
#endif
let allTests = testList "All Tests" []

[<EntryPoint>]
let main argv =
    printfn "Running tests" // added for sanity
#if FABLE_COMPILER_PYTHON
    Pyxpecto.runTests allTests
#endif
#if FABLE_COMPILER_JAVASCRIPT
    Mocha.runTests allTests
#endif
#if !FABLE_COMPILER
    Tests.runTestsWithCLIArgs [] argv allTests
#endif

I did go through the exercise of refactoring where I would consider all paths as valid and ended up coming up with the below code. Changing some of the #ifs to #elifs makes more sense (at least to me) since I don't believe we can have more than one compiler directive at a time. However, fantomas does encounter some issues with this approach.

#r "nuget: Expecto"

#if FABLE_COMPILER_PYTHON
open Fable.Pyxpecto
#elif FABLE_COMPILER_JAVASCRIPT
open Fable.Mocha
#elif FABLE_COMPILER
#else
open Expecto
[<Tests>] //needed for `dotnet test` to work
#endif
let allTests = testList "All Tests" [ ]

[<EntryPoint>]
let main argv =
#if FABLE_COMPILER_PYTHON
    Pyxpecto.runTests allTests
#elif FABLE_COMPILER_JAVASCRIPT
    Mocha.runTests allTests
#elif FABLE_COMPILER
#else
    Tests.runTestsWithCLIArgs [] argv allTests
#endif

After running fantomas, I get the following:

[20:30:46 ERR] Failed to format file: test.fsx : ParseException
  [{ Severity = Error
     SubCategory = "parse"
     Range = Some (5,1--5,5)
     ErrorNumber = Some 10
     Message =
      "Unexpected keyword 'elif' in directive. Expected identifier or other token." };
   { Severity = Error
     SubCategory = "parse"
     Range = Some (7,1--7,5)
     ErrorNumber = Some 10
     Message =
      "Unexpected keyword 'elif' in directive. Expected identifier or other token." };
   { Severity = Error
     SubCategory = "parse"
     Range = Some (18,1--18,5)
     ErrorNumber = Some 10
     Message =
      "Unexpected keyword 'elif' in directive. Expected identifier or other token." }]

---

Peeking through the code I think this may be the area to start looking in regards to supporting #elif if we think that is a desired feature. Just let me know how I can help if we see the #elif as a desired feature and I can try submitting a PR 😄

[nojaf]

#elif isn't a thing, https://learn.microsoft.com/en-us/dotnet/fsharp/language-reference/compiler-directives#preprocessor-directives

fsharp/fslang-suggestions#1370

[1eyewonder]

Well that would be why it doesn't work then 😅
I will go ahead and update my code accordingly then. Thanks for the help

[nojaf]

Alright, anything actionable left for Fantomas here?

[1eyewonder]

Nope! I feel silly but happy I learned this about F#. I didn't know it had different directive support than C#