A reusable `_Imports.razor` or `<Using />` for Razor Components

[datvm]

Is there an existing issue for this?

• I have searched the existing issues

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

Currently, the only global using equivalent for Razor is the _Imports.razor which unfortunately is not reusable or even modular in anyway. Meanwhile, C# has serveral ways: global using from multiple files, <Using Include="namespace" /> which can also be reused by using <Import /> from targets.

Describe the solution you'd like

1. Razor Components should honor <Using /> when generating component. To prevent breaking change, maybe it should be opt-in with a property switch:

	<PropertyGroup>
		<RazorUsesUsings>true</RazorUsesUsings>
	</PropertyGroup>

	<ItemGroup>
		<Using Include="Microsoft.AspNetCore.Components" />
		<Using Include="Microsoft.AspNetCore.Components.Forms" />
		<Using Include="Microsoft.AspNetCore.Components.Web" />
	</ItemGroup>

At first I thought about a new tag like RazorUsing but I think it's a bad idea because in the end it mostly will just repeat whatever Using there are.

2. A reusable _Imports.razor component. I am not sure how feasible it should be, but it could be like this:

Common1.razor

<Using Namespace="Microsoft.AspNetCore.Components" />
<Using Namespace="Microsoft.AspNetCore.Components.Forms" />

_Imports.razor

<Namespace.Common1 />
<Namespace.Common2 />

Additional context

No response

[javiercn]

@datvm thanks for contacting us.

This is not a direction we plan to take in the near term. This is something that developers can do themselves or someone in the community can build a package for. Here is a rough example of how this can be done inline.

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <UsingTask TaskName="GenerateRazorImportsTask"
             TaskFactory="RoslynCodeTaskFactory"
             AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
    <ParameterGroup>
      <UsingItems ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="false" />
      <ProjectDir ParameterType="System.String" Required="true" />
    </ParameterGroup>
    <Task>
      <Reference Include="System.Runtime" />
      <Reference Include="Microsoft.CodeAnalysis" />
      <Reference Include="Microsoft.CodeAnalysis.CSharp" />
      <Using Namespace="System" />
      <Using Namespace="System.IO" />
      <Using Namespace="System.Linq" />
      <Using Namespace="System.Text" />
      <Using Namespace="Microsoft.Build.Framework" />
      <Using Namespace="Microsoft.Build.Utilities" />
      <Using Namespace="Microsoft.CodeAnalysis" />
      <Using Namespace="Microsoft.CodeAnalysis.CSharp" />
      <Code Type="Fragment" Language="cs"><![CDATA[
public override bool Execute()
{
    try
    {
        var items = (UsingItems ?? new ITaskItem[0]).Select(i=>i.ItemSpec).Where(s=>!string.IsNullOrWhiteSpace(s)).Distinct().ToArray();
        var outPath = Path.Combine(ProjectDir, "_Imports.razor");
        var sb = new StringBuilder();
        foreach(var ns in items)
        {
            // use Roslyn to normalize namespace text
            var node = Microsoft.CodeAnalysis.CSharp.SyntaxFactory.UsingDirective(Microsoft.CodeAnalysis.CSharp.SyntaxFactory.ParseName(ns)).NormalizeWhitespace();
            var text = node.ToFullString().TrimEnd(';').Replace("using ","@using ");
            sb.AppendLine(text);
        }
        var content = sb.ToString();
        Directory.CreateDirectory(ProjectDir);
        if (File.Exists(outPath) && File.ReadAllText(outPath) == content) { Log.LogMessage(MessageImportance.Low, "_Imports.razor up-to-date"); return true; }
        File.WriteAllText(outPath, content, Encoding.UTF8);
        Log.LogMessage(MessageImportance.Normal, $"Wrote {outPath}");
        return true;
    }
    catch(Exception ex) { Log.LogErrorFromException(ex,true); return false; }
}
]]></Code>
    </Task>
  </UsingTask>

  <Target Name="GenerateRazorImports" BeforeTargets="RazorGenerate;CoreCompile">
    <GenerateRazorImportsTask UsingItems="@(Using)" ProjectDir="$(MSBuildProjectDirectory)" />
    <ItemGroup>
      <AdditionalRazorSource Include="$(MSBuildProjectDirectory)\_Imports.razor" />
    </ItemGroup>
  </Target>

</Project>