`System.FormatException` for FormattableString with `{{ }}` content

[mrange]

Apologies if this is already reported but didn't find a matching report.

Repro steps

This program below crashes for me with System.FormatException

open System

let s   : string            = $"{{ {1} }}"
let fs  : FormattableString = $"{{ {1} }}"

// Works
printfn "s: %s" <| s
// Crashes with `System.FormatException`
printfn "fs: %s" <| fs.ToString ()

Expected behavior

I expect the program to print

{ 1 }
{ 1 }

Actual behavior

s: { 1 }
Unhandled exception. System.FormatException: Input string was not in a correct format.
   at System.Text.ValueStringBuilder.ThrowFormatError()
   at System.Text.ValueStringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.Format(IFormatProvider provider, String format, Object[] args)
   at System.Runtime.CompilerServices.FormattableStringFactory.ConcreteFormattableString.ToString(IFormatProvider formatProvider)
   at System.FormattableString.ToString()

Known workarounds

None known

Related information

I tried writing a similar program in C# and it produced the expected results

string              s   = $"{{ {1} }}";
FormattableString   fs  = $"{{ {1} }}";

Console.WriteLine(s);
Console.WriteLine(fs.ToString());

When printing the F# FormattableString.Format it is : { {0} }
When printing the C# FormattableString.Format it is : {{ {0} }}

• Windows 10
• net6.0
• Visual Studio 2022 Preview 5.0

[kerams]

$"{{}}" blows up too.

[mrange]

I see now this this seems to be a duplicate of: #11782