Question about changed behavior of string interpolations in NativeAOT in the .NET 11 rc1 SDK #20757

Hi,

Not sure if this is a bug, or an expected change after #19971, but as it came across as a breaking change to me I'll ask in case.

When doing testing with fable-hub/Scriptorium#21 I noticed that if I have the code

let now = System.DateTime.UtcNow

let startAt =
    $"%02d{now.Hour}:%02d{now.Minute}:%02d{now.Second}"

and compile that with NativeAOT using the .NET 10 SDK then the resulting executable works correctly, but compiling the same code with the .NET11-RC1 SDK then it crashes at runtime with an exception similar to the one in fable-hub/Scriptorium#21.

This doesn't seem ideal, even given the known issues with F# style format specifiers, if it worked before and doesn't now?

fwiw, looking at the binary with ILSpy, the .NET 10 build that works decompiles as

string startAt2 = (startAt2@10 = ExtraTopLevelOperators.PrintFormatToString(new PrintfFormat<string, Unit, string, string, Tuple<int, int, int>>("%02d%P():%02d%P():%02d%P()", new object[3]
{
    Program.now.Hour,
    Program.now.Minute,
    Program.now.Second
}, null)));

and the .NET 11 build that doesn't shows as

string startAt2 = (startAt2@9 = ExtraTopLevelOperators.PrintFormatToString(new PrintfFormat<FSharpFunc<int, string>, Unit, string, string, int>("%02d")).Invoke(Program.now.Hour) + ":" + ExtraTopLevelOperators.PrintFormatToString(new PrintfFormat<FSharpFunc<int, string>, Unit, string, string, int>("%02d")).Invoke(Program.now.Minute) + ":" + ExtraTopLevelOperators.PrintFormatToString(new PrintfFormat<FSharpFunc<int, string>, Unit, string, string, int>("%02d")).Invoke(Program.now.Second));

Known workarounds

Doing $"{now.Hour:D2}:{now.Minute:D2}:{now.Second:D2}" works in the RC1 SDK, so it can at least be made to work that way.

Thanks.