Update implicit global usings feature to address issues

[DamianEdwards]

The new implicit global usings feature added to the SDK in 6.0.100-preview.7 has caused a few issues in some important scenarios such that some changes will be made to mitigate them and generally improve its usability.

These changes are targeting 6.0.100-rc.1

Items:

• Rename the MSBuild property from <DisableImplicitNamespaceImports> to <ImplicitUsings>
  • Note this is for C# only
  • Visual Basic will continue to use the <DisableImplicitNamespaceImports> property for disabling implicit namespace imports
• Add the <ImplicitUsings> property to the schema file so it appears in statement completion
• Change the defined conditions to only enable adding the implicit usings from the SDK when the <ImplictUsings> property is set to "true" or "enable"
  • The existing conditions based on TFM should be removed
  • The only condition for adding the implicit usings as defined in the SDK will be the check that <ImplicitUsings> is equal to "true" or "enable"
• Rename the item type that specifies the global namespaces to emit to the generated .cs file from <Import> to <Using>
  • Note this is for C# only
  • Visual Basic will continue to use the <Import> item type for specifying namespaces to import
• Update schema for ImplicitUsings feature msbuild#6745
• Ensure the generated file is still emitted if any <Using> items are declared (even if <ImplicitUsings> is false)
• Ensure that implicit <Import> items for Visual Basic are not changed from what they were in .NET 5
• Update processing of <Using> items to support defining using [alias] and using static [type] as well as using [namespace], e.g.:
  • <Using Include="Microsoft.AspNetCore.Http.Results" Alias="Results" />
    emits global using Results = global::Microsoft.AspNetCore.Http.Results;
  • <Using Include="Microsoft.AspNetCore.Http.Results" Static="True" />
    emits global using static global::Microsoft.AspNetCore.Http.Results;
  • <Using Include="Microsoft.AspNetCore.Http" />
    emits global using global::Microsoft.AspNetCore.Http;
• Update the C# project templates to enable implicit usings for new .NET 6 projects, i.e. include <ImplicitUsings>enable</ImplicitUsings> in the .csproj file
  • This will be tracked by issues in the relevant repos for each template
  • Update web project templates to opt-in to ImplicitUsings feature aspnetcore#35131
  • Update console & classlib project templates to opt-in to ImplicitUsings feature templating#3619
  • Update C# templates with global usings winforms#5074

Example project file content after these changes:

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

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <Using Include="My.Awesome.Namespace" />
  </ItemGroup>
</Project>

[alexrp]

Could global using static support also be included?

[DamianEdwards]

@alexrp yes that was the intent but I didn't capture it properly in the item RE using alias support. Updated to make it clearer.

[dougbu]

nit: Suggest avoiding any parsing of the <Using /> item spec e.g.

<Using Include="Microsoft.AspNetCore.Http.Results" Alias="Results" />

and

<Using Include="Microsoft.AspNetCore.Results" Static="true" />

[DamianEdwards]

Thanks @dougbu I had the exact same thought last night and glad others agree. Will update the description.