Update C# templates to top level statements

[RussKie]

Top level statements have been released in .NET 5 and C# 9. There are a number of active internal discussion about updating other templates (e.g. ASP.NET Core) to use the top level statements approach.

As discussed in dotnet/designs#223 (comment) C# Windows Forms apps can be written as top level programs today as well, though [STAThread] make it a little awkward. So we can consider updating our application template

winforms/pkg/Microsoft.Dotnet.WinForms.ProjectTemplates/content/WinFormsApplication-CSharp/Program.cs

Lines 1 to 23 in c76a4a4

	using System;
	using System.Collections.Generic;
	using System.Linq;
	using System.Threading.Tasks;
	using System.Windows.Forms;
	namespace Company.WinFormsApplication1
	{
	static class Program
	{
	/// <summary>
	/// The main entry point for the application.
	/// </summary>
	[STAThread]
	static void Main()
	{
	Application.SetHighDpiMode(HighDpiMode.SystemAware);
	Application.EnableVisualStyles();
	Application.SetCompatibleTextRenderingDefault(false);
	Application.Run(new Form1());
	}
	}
	}

...and rewrite it as follows:

using System.Threading;
using System.Windows.Forms;
using Company.WinFormsApplication1;

// It is unfortunate but we have to set it to Unknown first.
Thread.CurrentThread.SetApartmentState(ApartmentState.Unknown);
Thread.CurrentThread.SetApartmentState(ApartmentState.STA);

Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(defaultValue: false);
Application.SetHighDpiMode(HighDpiMode.PerMonitorV2);

Application.Run(new Form1());

When dotnet/designs#223 will be implemented the template can be further simplified, and would look something like this:

using System.Threading;
using System.Windows.Forms;
using Company.WinFormsApplication1;

// It is unfortunate but we have to set it to Unknown first.
Thread.CurrentThread.SetApartmentState(ApartmentState.Unknown);
Thread.CurrentThread.SetApartmentState(ApartmentState.STA);

ApplicationConfiguration.Initialize();

Application.Run(new Form1());

And, generally speaking, there's nothing that prevents moving Thread.CurrentThread.SetApartmentState(...) calls into the source generated ApplicationConfiguration.Initialize() method:

using System.Threading;
using System.Windows.Forms;
using Company.WinFormsApplication1;

ApplicationConfiguration.Initialize();

Application.Run(new Form1());

[RussKie]

[AraHaan]

I would rather the Application.Run() to also be moved to the Initialize method that is source generated and take in the form instance that should be new'd up in that call so it could be simplified to just:

// make these global usings in "GlobalUsings.cs".
using System.Threading;
using System.Windows.Forms;
using Company.WinFormsApplication1;

ApplicationConfiguration.Initialize(() => new Form1());

So then in the end the actual Program.cs file could then be chopped down to just a single line of actual code with the Initialize method running that lambda inside when it calls Run for you.

[RussKie]

We won't be changing our templates to use the top level statements (#5071). A typical Windows Forms app consist of multiple types split across multiple files (e.g. Form1.cs and Form1.Designer.cs) that won't work with top level statements.

[Amy-Li03]

@RussKie Verified this issue on .NET 6.0 RC1 latest build: 6.0.10-rc.1.21417.19 + binaries build from main branch under dotnet/winforms repo, after replace following codes in Program.cs file:

Application.SetHighDpiMode(HighDpiMode.SystemAware);
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);

with
ApplicationConfiguration.Initialize();

this code is not recognized as following screenshot, want to confirm with you do we need to do some other actions at here?

[RussKie]

<LangVersion>preview</LangVersion> in csproj until .NET 6.0 goes GA.

[Amy-Li03]

You mean preview will show in csproj until .NET 6.0 goes GA, we can verify this issue at then?

[RussKie]

We use Source Generators API v2, which are behind the "preview" lang version. @chsienki @sharwell the langversion=preview won't be require when .NET 6.0 GAs, right?

[chsienki]

@RussKie We just (today) merged the change that removes the requirement. .NET 6.0 GA will enable V2 generators by default.

[RussKie]

Awesome! 🎉

[Amy-Li03]

Verified this issue with .NET 6.0 RC2 latest build: 6.0.10-rc.2.21429.3, when using ApplicationConfiguration.Initialize() method on Program.cs or use top level statements, winforms .NET core project can build and run successfully.

[AraHaan]

Does this mean it also adds the [main: STAThread] to the top level program in that case?

[RussKie]

AFAIK there is no such thing as [main: STAThread], though it is being discussed.
In the case of top level statements ApplicationConfiguration.Initialize() emits this:

winforms/src/System.Windows.Forms.Analyzers.CSharp/src/System/Windows/Forms/Generators/ApplicationConfigurationInitializeBuilder.cs

Lines 93 to 95 in 07f6de3

	// Set STAThread
	Thread.CurrentThread.SetApartmentState(ApartmentState.Unknown);
	Thread.CurrentThread.SetApartmentState(ApartmentState.STA);