dotnet run file custom entrypoint support

[WeihanLi]

Is your feature request related to a problem? Please describe.

When there's no entry point for the file(s), maybe we could allow the user provider a custom entry point to execute, hope it could be part of the dotnet run file experience #48170

Describe the solution you'd like

When there's no entry point in the file(s), and user user-provided entry point is valid, mark it as the entry point other than fail.

For example, we have the following file named helper.cs

public class Helper
{
  public static void AddTest()
  {
    var a = 1;
    var b = 2;
    Console.WriteLine(a + b);
  }

  public static void HelloTest()
  {
    Console.WriteLine("Hello World!");
  }
}

dotnet helper.cs --entry HelloTest

output:

Hello World!

Additional context

[DamianEdwards]

Custom entry-point method names are not currently supported by C#. They must fit one of the following signatures:

• static void Main(string[] args)
• static int Main(string[] args)
• static void Main()
• static int Main()
• Async versions of any of the above

To support a method name other than Main would require a change to C# itself and as such this feature request is best made in that repo.

[WeihanLi]

That would be a pity, think it may be possible to support via a custom generator to generate an entrypoint