Developers can safely trim their apps which use Dependency Injection to reduce the size of their apps

[samsp-msft]

Source Generators are a new technology that was added to Roslyn in the .NET 5 timeframe, but we have not yet utilized them by creating generators to assist with runtime and framework features. We will work to define customer scenarios in more detail here with customer development.

Code that uses runtime reflection and reflection.emit causes issues for Trimming and Native AOT. Source generators can be used to generate alternative code at build time that is static so can be used in conjunction with Trimming and AOT. Work on trimming ASP.NET apps has revealed where there are current limitations that can be solved by source generators.

This item tracks creating a Source Generator for Dependency Injection (DI).

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[samsp-msft]

Refactored from #43545

Tagging subscribers to this area: @eerhardt, @maryamariyan
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Issue content:	Source Generators are a new technology that was added to Roslyn in the .NET 5 timeframe, but we have not yet utilized them by creating generators to assist with runtime and framework features. We will work to define customer scenarios in more detail here with customer development. Code that uses runtime reflection and reflection.emit causes issues for Trimming and Native AOT. Source generators can be used to generate alternative code at build time that is static so can be used in conjunction with Trimming and AOT. Work on trimming ASP.NET apps has revealed where there are current limitations that can be solved by source generators. This item tracks creating a Source Generator for Dependency Injection (DI).
Issue author:	samsp-msft
Assignees:	danmosemsft, samsp-msft
Milestone:	-

[danmoseley]

@danroth27 how important is DI to Blazor scenarios? I suspect this story would be expensive, so I'd like to understand whether it's particularly valuable.
@glennc My understanding is that this is mainly about startup of ASP.NET apps, so it would not be P0 for this release.

cc @marek-safar

[danroth27]

@danmosemsft DI is used heavily in both Blazor and ASP.NET Core.

[eerhardt]

DI is used heavily in both Blazor and ASP.NET Core.

@danroth27 - But how important is it to have a Source Generator for DI for Blazor? We are able to use DI in a Blazor WASM app just fine in 5.0 without a Source Generator. Is one critical for 6.0 scenarios?

Note: For Blazor WASM, we currently use a "Reflection" provider for DI since RuntimeFeature.IsDynamicCodeCompiled is false on Blazor WASM:

runtime/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceCollectionContainerBuilderExtensions.cs

Lines 66 to 74 in 7b93881

	if (RuntimeFeature.IsDynamicCodeCompiled)
	{
	engine = new DynamicServiceProviderEngine(services);
	}
	else
	{
	// Don't try to compile Expressions/IL if they are going to get interpreted
	engine = new RuntimeServiceProviderEngine(services);
	}

[ericstj]

@davidfowl was mentioning that this was important to investigate in 6.0 but not "do".