[Feature Proposal]: Support isolated islands of assemblies for AOT compilation

[jevansaks]

Background

Our scenario is we have multiple teams working independently on apps/components that need to ship together in a single package. To save space in that package, we are going to AOT compile all of these apps/components together (as opposed to AOT compiling them individually). The goal is to fold together similar code and de-duplicate .NET runtime and .NET libraries which are heavily overlapping between these components.

However, the components may take the same nuget dependencies at different versions. In order to AOT compile them together we must choose one of the nuget dependencies for the AOT compilation but if the API contract across nuget versions is not stable, this doesn't work.

For nuget packages we own I have figured out a trick that I can encode the version number of the nuget package into the AssemblyName of the dlls, which helps partition these assemblies in the AOT compilation because they are now distinct from the perspective of ILC.

Feature Proposal

The request is to support loading conflicting assembly references in "islands" for AOT compilation. In terms of .NET APIs this is similar to AssemblyLoadContext where I want to isolate assembly loads within a single runtime, but in AOT compilation I don't have any way to influence how the assemblies are loaded into ILC.

From an authoring perspective this might look an attribute on the Reference tag, similar to "Aliases".

    <Reference Include="NugetPackage.1.1.0\Library.dll" AssemblyLoadContext="Island1" />
    <Reference Include="NugetPackage.1.2.0\Library.dll" AssemblyLoadContext="Island2" />

Alternatives considered

The extern alias is similar to what we want here, but I don't have any influence over the consuming assemblies as the conflicting dependencies may be via transitive nuget references and not in assemblies I have control over.

I also have thought about doing ildasm , replacing assembly references with versioned assembly names , and then putting it back together with ilasm. I haven't tried this, but if folks this might be viable I can pursue it.

I'm open to other suggestions for how to accomplish this goal!

[jevansaks]

CC @agocke @MichalStrehovsky

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[jkotas]

You are asking for package shading (it is what this feature is called in Java and other ecosystem). There is a stale proposal at dotnet/designs#242 .

I do not think that NativeAOT compiler is the right place to solve it.

[jkotas]

Duplicate of NuGet/Home#12400 and related issues.

[agocke]

Yup, this a fairly common and complex feature. Some languages, like Go, have decided that it's not in the scope of tooling at all. They recommend that all libraries which have breaking changes must include a version bump and include that version number in the package name: https://go.dev/ref/mod#major-version-suffixes. Either way, I agree that the AOT compiler isn't the place to solve this. Closing as a dup of the issues above.