Update C# templates with global usings

[RussKie]

We can simplify our templates with global usings and have them implemented similar to this:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework Condition="'$(TargetFrameworkOverride)' == ''">FrameworkParameter-windows</TargetFramework>
    <TargetFramework Condition="'$(TargetFrameworkOverride)' != ''">TargetFrameworkOverride-windows</TargetFramework>
    <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">Company.WinFormsApplication1</RootNamespace>
    <LangVersion Condition="'$(langVersion)' != ''">$(ProjectLanguageVersion)</LangVersion>
    <Nullable Condition="'$(Nullable)' == 'true'">enable</Nullable>
    <UseWindowsForms>true</UseWindowsForms>
  </PropertyGroup>

+ <ItemGroup>
+   <Compile Include=".usings" />
+ </ItemGroup>

</Project>

A sample .using file:

global using System;
global using System.Collections.Generic;
global using System.Drawing;
global using System.Linq;
global using System.Threading.Tasks;
global using System.Windows.Forms;

This list of usings looks sensible, but it is up for a discussion.

Credits for this idea go to https://github.com/khalidabuhakmeh/CsharpTenFeatures.

At some point in the future when dotnet/aspnetcore#32451 settles, we could follow in their steps and bake all typical Windows Forms usings into the Windows Desktop SDK.

[AraHaan]

I would rather name the file GlobalUsings.cs 🤔.

Bonus points: using json to store the using directives that should be global then use a source generator to generate the global usings code file. In which case I think using a json file to store the global usings is a good idea.

Also which future public SDK might come with global usings shipped with it so it would not require any preview feeds / compiler packages to use those new features then?

[RussKie]

I would rather name the file GlobalUsings.cs 🤔.

Why?

Bonus points: using json to store the using directives that should be global then use a source generator to generate the global usings code file. In which case I think using a json file to store the global usings is a good idea.

Why? And why do we need source generators here?

[AraHaan]

I would rather name the file GlobalUsings.cs 🤔.

Why?

So that way the user could clearly see where the usings are.

Bonus points: using json to store the using directives that should be global then use a source generator to generate the global usings code file. In which case I think using a json file to store the global usings is a good idea.

Why? And why do we need source generators here?

I just stated it as a possible option that a developer could opt into to have the global usings file get source generated for them based on a json file to define which global users it should contain.

[DamianEdwards]

@RussKie the SDK feature was just merged. The epic has been updated with details of which namespaces are imported by default by the various SDKs. Please add the details for WinForms at your convenience.

[RussKie]

Refer to dotnet/sdk#19521 for new directions.

[DamianEdwards]

@RussKie are you planning to bring this change through ASK mode for rc.1?