sdk: `dotnet run` gives `ArgumentOutOfRangeException` error at `TryGetTargetArchitecture` method

Describe the bug

I installed .NET 6.0.1 SDK, and turned out that I cannot use command dotnet run at all, because it keeps giving me ArgumentOutOfRangeException. However, it is successful to run dotnet build then dotnet [path-to-dll] or dotnet watch run instead. The full error message:

System.ArgumentOutOfRangeException: startIndex cannot be larger than length of string. (Parameter 'startIndex')
   at System.String.Substring(Int32 startIndex, Int32 length)
   at Microsoft.DotNet.Tools.Run.RunCommand.TryGetTargetArchitecture(String runtimeIdentifier, Nullable`1& targetArchitecture)
   at Microsoft.DotNet.Tools.Run.RunCommand.GetTargetCommand()
   at Microsoft.DotNet.Tools.Run.RunCommand.Execute()
   at Microsoft.DotNet.Tools.Run.RunCommand.Run(String[] args)
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, TimeSpan startupTime, ITelemetry telemetryClient)
   at Microsoft.DotNet.Cli.Program.Main(String[] args)

I have tried reinstalled using SDK Installer, Visual Studio Installer, and binaries zip file. All gave me the same result.

So I decided to pull the branch release/6.0.1xx from this repository, and modified the method TryGetTargetArchitecture in file src\Cli\dotnet\commands\dotnet-run\RunCommand.cs to add try&catch blocks as following to debug the behaviour of the command:

private static bool TryGetTargetArchitecture(string runtimeIdentifier, out Architecture? targetArchitecture)
{
    targetArchitecture = null;
    int separator = runtimeIdentifier.LastIndexOf("-");
    if (separator < 0)
    {
        return false;
    }

    try // ↓ MODIFIED FROM HERE
    {
        targetArchitecture = runtimeIdentifier.Substring(separator + 1).ToLowerInvariant() switch
        {
            "arm" => Architecture.Arm,
            "arm64" => Architecture.Arm64,
            "x64" => Architecture.X64,
            "x86" => Architecture.X86,
            _ => null
        };
    }
    catch
    {
        Console.WriteLine($"runtimeIdentifier = {runtimeIdentifier}");
        Console.WriteLine($"runtimeIdentifier.Length = {runtimeIdentifier.Length}");
        Console.WriteLine("runtimeIdentifier (CharArray) = " + String.Join(", ", runtimeIdentifier.ToCharArray().Select(x => $"'{x}'")));
        Console.WriteLine($"separator = {separator}");
    } // ↑ MODIFIED UNTIL HERE

    return targetArchitecture != null;
}

Here is the result:

runtimeIdentifier =
runtimeIdentifier.Length = 0
runtimeIdentifier (CharArray) =
separator = 0

runtimeIdentifier = win-x64
runtimeIdentifier.Length = 7
runtimeIdentifier (CharArray) = 'w', 'i', 'n', '-', 'x', '6', '4'
separator = 7

Oddly, it seems that String.LastIndexOf in my machine does not work as expected, and that cause it returns an incorrect character index.

I don’t know what in my machine breaks the LastIndexOf, but it would be better if we have a safer logic in this method to prevent the similar problem.

---

Further technical details

• Include the output of dotnet --info

.NET SDK (reflecting any global.json):
 Version:   6.0.100
 Commit:    9e8b04bbff

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22000
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Users\xxx\exe\dotnet\sdk\6.0.100\

Host (useful for support):
  Version: 6.0.0
  Commit:  4822e3c3aa

.NET SDKs installed:
  6.0.100 [C:\Users\xxx\exe\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.0 [C:\Users\xxx\exe\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.0 [C:\Users\xxx\exe\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.0 [C:\Users\xxx\exe\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download