AddMissingEqualsToTypeDefinitionCodeFixProvider crash

[0101]

This suddenly popped up when editing some code - which wasn't relevant to the code fix (no type in sight). But finding the broken ExactlyOne should be enough to fix this.

System.ArgumentException : The input sequence contains more than one element.
Parameter name: source
   at Microsoft.FSharp.Collections.SeqModule.ExactlyOne[T](IEnumerable`1 source)
   at async StartupCode$FSharp-Editor(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.CodeFixExtensions.CodeFixContext-RegisterFsharpFix@85(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.CodeFixes.CodeFixService.GetCodeFixesAsync(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)

[vzarytovskii]

Yeah, as a rule of thumb, we should not be throwing in vs, but instead reporting errors using built-in mechanism

[psfinaki]

Repro:

let f x = 
    match x with
    | _ ->
        let _ = [
            x with
        ]

repro.mp4

Indeed, we have two different FS0010 here:

[0101]

I would suggest removing all unsafe operations like exactlyOne, head, etc. From the code fixes (or really anywhere where it can crash in VS) regardless of if the underlying cause is legitimate. Instead of crashing report telemetry so we'll find out about it.

Could be also a nice analyzer to highlight all of these.