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Fable's JsInterop ? dynamic access operator causes formatting error #3135

Closed
#3218
Closed
Fable's JsInterop ? dynamic access operator causes formatting error#3135
#3218
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bug (soundness)

Description

@joprice
joprice
opened on Nov 4, 2024

Issue created from fantomas-online

Code

Jest.expect(json)?oMatchSnapshot ()

Error

System.Exception: cannot determine if Expr AppLongIdentAndSingleParenArg
  Fantomas.Core.SyntaxOak+ExprAppLongIdentAndSingleParenArgNode is uppercase or lowercase
   at Microsoft.FSharp.Core.PrintfModule.PrintFormatToStringThenFail@1448.Invoke(String message)
   at Fantomas.Core.CodePrinter.sepSpaceBeforeParenInFuncInvocation(Expr functionExpr, Expr argExpr, Context ctx) in /_//src/Fantomas.Core/CodePrinter.fs:line 2549
   at Fantomas.Core.CodePrinter.genExpr@1036-197.Invoke(Context ctx)
   at Fantomas.Core.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /_//src/Fantomas.Core/Context.fs:line 430
   at Fantomas.Core.Context.shortExpressionWithFallback(FSharpFunc`2 shortExpression, FSharpFunc`2 fallbackExpression, Int32 maxWidth, FSharpOption`1 startColumn, Context ctx) in /_//src/Fantomas.Core/Context.fs:line 616
   at Fantomas.Core.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /_//src/Fantomas.Core/Context.fs:line 430
   at Fantomas.Core.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /_//src/Fantomas.Core/Context.fs:line 430
   at Fantomas.Core.Context.col[T](FSharpFunc`2 f', IEnumerable`1 c, FSharpFunc`2 f, Context ctx) in /_//src/Fantomas.Core/Context.fs:line 463
   at Fantomas.Core.CodePrinter.genFile@4066-4.Invoke(Context ctx)
   at Fantomas.Core.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /_//src/Fantomas.Core/Context.fs:line 430
   at Fantomas.Core.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /_//src/Fantomas.Core/Context.fs:line 430
   at Fantomas.Core.CodeFormatterImpl.formatAST(ParsedInput ast, FSharpOption`1 sourceText, FormatConfig config, FSharpOption`1 cursor) in /_//src/Fantomas.Core/CodeFormatterImpl.fs:line 74
   at Fantomas.Core.CodeFormatterImpl.formatDocument@89-3.Invoke(Unit unitVar) in /_//src/Fantomas.Core/CodeFormatterImpl.fs:line 89
   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 using the ? operator on the result of a tupled function call, a parse error is hit. A workaround is to call the first function without parens: (Jest.expect json)?oMatchSnapshot ()

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 11/04/2024

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.

Activity

  1. nojaf commented on Nov 5, 2024

    @nojaf
    nojaf
    on Nov 5, 2024
    Contributor

    Hello,

    Thanks for reporting this problem!

    You would need to extend

    fantomas/src/Fantomas.Core/CodePrinter.fs

    Lines 44 to 63 in b7dca79

    match expr with
    | Expr.Ident ident -> upperOrLower ident.Text
    | Expr.OptVar node -> lastFragmentInList node.Identifier
    | Expr.Chain node ->
    match List.tryLast node.Links with
    | None
    | Some(ChainLink.Dot _) -> LowercaseExpr
    | Some(ChainLink.Identifier e)
    | Some(ChainLink.Expr e) -> (|UppercaseExpr|LowercaseExpr|) e
    | Some(ChainLink.AppParen appParen) -> (|UppercaseExpr|LowercaseExpr|) appParen.FunctionName
    | Some(ChainLink.AppUnit appUnit) -> (|UppercaseExpr|LowercaseExpr|) appUnit.FunctionName
    // Questionable
    | Some(ChainLink.IndexExpr _) -> LowercaseExpr
    | Expr.DotIndexedGet node -> (|UppercaseExpr|LowercaseExpr|) node.ObjectExpr
    | Expr.TypeApp node -> (|UppercaseExpr|LowercaseExpr|) node.Identifier
    | Expr.Dynamic node -> (|UppercaseExpr|LowercaseExpr|) node.FuncExpr
    | Expr.AppSingleParenArg node -> (|UppercaseExpr|LowercaseExpr|) node.FunctionExpr
    | Expr.Paren node -> (|UppercaseExpr|LowercaseExpr|) node.Expr
    | Expr.App node -> (|UppercaseExpr|LowercaseExpr|) node.FunctionExpr
    | _ -> failwithf "cannot determine if Expr %A is uppercase or lowercase" expr

    with Expr.AppLongIdentAndSingleParenArg where you want to check the FunctionName I think.

    Would you be interested in sending a PR for this?

  2. nojaf
    added
    bug (soundness)
    on Nov 5, 2024
  3. nojaf
    added a commit that references this issue on Feb 26, 2026

    Fix dynamic operator on qualified function call result (fsprojects#3135)

    e9fad2e
  4. nojaf
    closed this as completedin #3218on Feb 27, 2026
  5. github-actions
    added a commit that references this issue on Sep 15, 2026

    Bump the dotnet-sidecars group with 6 updates (#257)

    5305a19
  6. tonycknight
    added 2 commits that reference this issue on Sep 21, 2026

    Bump the packages group with 5 updates (#106)

    8692f77

    Bump the packages group with 6 updates (#84)

    e92f72f
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