"cannot determine if synExpr Paren" when Lambda after If expression

[jindraivanek]

Issue created from fantomas-online

Code

(if true then foo else goo) (fun _ -> 42)

Error

System.Exception: cannot determine if synExpr Paren
  (IfThenElse
     (tmp.fsx (1,1--1,3), false, Const (Bool true, tmp.fsx (1,4--1,8)),
      tmp.fsx (1,9--1,13), Ident foo, Some tmp.fsx (1,18--1,22),
      Some (Ident goo), Yes tmp.fsx (1,1--1,13), false, tmp.fsx (1,1--1,13),
      tmp.fsx (1,1--1,26)), tmp.fsx (1,0--1,1), Some tmp.fsx (1,26--1,27),
   tmp.fsx (1,0--1,27)) is uppercase or lowercase
   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.CodePrinter.sepSpaceAfterFunctionName@2074.Invoke(Context ctx) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodePrinter.fs:line 2074
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.Context.shortExpressionWithFallback(FSharpFunc`2 shortExpression, FSharpFunc`2 fallbackExpression, Int32 maxWidth, FSharpOption`1 startColumn, Context ctx) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 879
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.Context.col[T](FSharpFunc`2 f', IEnumerable`1 c, FSharpFunc`2 f, Context ctx) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 607
   at Fantomas.CodePrinter.genImpFile@96-6.Invoke(Context ctx) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodePrinter.fs:line 96
   at Fantomas.Context.op_PlusGreater(FSharpFunc`2 ctx, FSharpFunc`2 f, Context x) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/Context.fs:line 502
   at Fantomas.CodeFormatterImpl.formatWith(ParsedInput ast, FSharpList`1 defines, FSharpList`1 hashTokens, FormatContext formatContext, FormatConfig config) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodeFormatterImpl.fs:line 388
   at Fantomas.CodeFormatterImpl.mapping@408-1.Invoke(Unit unitVar) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodeFormatterImpl.fs:line 408
   at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvoke[T,TResult](AsyncActivation`1 ctxt, TResult result1, FSharpFunc`2 part2) in D:\a\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 446
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in D:\a\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 105

Problem description

Extra information

• The formatted result breaks by code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.

Options

Fantomas 4.6 branch at 1/1/1990

Default Fantomas configuration

[nojaf]

This happens as well with (foo) (fun _ -> 42), I believe the Paren(Lambda _) might be relevant here.

[nojaf]

As (if true then foo else goo) (42) does seem to work.