Blazor WASM with linker enabled downloads unused dependencies during boot

[isc30]

The linker in Blazor WASM is including dependencies that aren't in use (in normal scenarios these would be stripped out by the compiler, which is what happens with the linker disabled (ok)).

When adding a reference (RCL project/nuget) to a project with Microsoft.AspNetCore.Components.WebAssembly.Build and BlazorWebAssemblyEnableLinking set to true, the linker will add the dependency project as a boot dependency inside blazor.boot.json even if it's not used at all.

If this reference is not used, the linker should detect it and not add it as a boot project. I suspect the problem is somewhere where we take the linker output and enumerate the blazor binaries based on it.

This issue doesn't happen with BlazorWebAssemblyEnableLinking disabled (the unused project is not even inside _framework/_bin) but StaticWebAssets are still there (ok).

To Reproduce

Please follow the steps to get this reproduced on your own repository.
In order to check the bug, this minimal example repository with the bug can be used.

Properly Working Example: With no Linker

1. Create a Blazor WASM project (host)
2. Add <BlazorWebAssemblyEnableLinking>false</BlazorWebAssemblyEnableLinking>
3. Create a RCL project (lib) with a Component and wwwroot/test.css as StaticWebAsset
4. Reference lib from host and use the Component from it
5. Build and Run
6. The DLL of lib appears inside blazor.boot.json and gets downloaded during startup (ok)
7. Navigate to _content/lib/test.css and see that the StaticWebAsset is available (ok)
8. Remove the runtime usage of lib by not using the Component anymore so the compiler strips it out
9. The DLL of the project is no longer inside blazor.boot.json and doesn't get downloaded during startup (ok)
10. The StaticWebAsset _content/lib/test.css is still available (ok)

Buggy Example: With Linker enabled

1. Use the project from the working example
2. Change it to use <BlazorWebAssemblyEnableLinking>true</BlazorWebAssemblyEnableLinking>
3. Reference lib from host and use the Component from it
4. Build and Run
5. The DLL of lib appears inside blazor.boot.json and gets downloaded during startup (ok)
6. Navigate to _content/lib/test.css and see that the StaticWebAsset is available (ok)
7. Remove the runtime usage of lib by not using the Component anymore so the compiler strips it out
8. The DLL of the project is still inside blazor.boot.json and still gets downloaded during startup (fail)
9. The StaticWebAsset _content/lib/test.css is still available (ok)

Further technical details

• ASP.NET Core version: 3.2.0-rc1.20223.4
• dotnet version: 3.1.201

Comments

This is a rather big bug. When including a NuGet package and using a small portion of it, the linker will still add every sub-reference, even if not used and the DLL could be skipped.

This should still preserve StaticWebAssets from the projects that don't need a runtime.

[mkArtakMSFT]

Thanks for contacting us.
The linker is only linking the framework binaries at the moment. We will be changing that in the future to trim also application binaries in the future.

[isc30]

Can we at least get an ItemGroup to be able to exclude some assemblies (and subassemblies) from the blazor.boot.json?
Disabling the linker seems useless in this situation