[TrimmableTypeMap] IDE Compile→SignAndroidPackage flow doesn't generate the typemap (DesignTimeBuildSignAndroidPackage)

[simonrozsival]

Summary

DesignTimeBuildSignAndroidPackage(NativeAOT) fails: the IDE-style flow (run Compile, then separately run SignAndroidPackage, both with BuildingInsideVisualStudio=true) never generates the trimmable typemap, so packaging errors:

Microsoft.Android.Sdk.TypeMap.Trimmable.targets(179,5): error :
  Trimmable typemap assembly list 'obj/Release/android-arm64/typemap/typemap-assemblies.txt' was not found.

Diagnosis (reproduced locally)

_GenerateTrimmableTypeMap is gated on '$(_OuterIntermediateOutputPath)' == '' (it is meant to run only in the RID-less outer build, because — per its comment — inner/design-time builds "lack the manifest template and full assembly set needed for correct deferred-registration propagation").

In the IDE flow with a RuntimeIdentifier:

• -t:Compile -p:BuildingInsideVisualStudio=true runs in the inner RID build (_OuterIntermediateOutputPath = obj/Release/android-arm64/, DesignTimeBuild = false), so _GenerateTrimmableTypeMap is skipped and produces no typemap-assemblies.txt.
• -t:SignAndroidPackage -p:BuildingInsideVisualStudio=true is also an inner RID build → _GenerateTrimmableTypeMap skipped again → _ReadGeneratedTrimmableTypeMapAssemblies finds no list and hard-errors (the empty-list fallback only applies when @(ReferencePath->Count()) == 0).

A normal single-invocation dotnet build works because the RID-less outer pass runs _GenerateTrimmableTypeMap first. The legacy _GenerateJavaStubs has no _OuterIntermediateOutputPath gate, so the legacy/CoreCLR path generates stubs in the inner build and this scenario passes.

Fix direction (needs design)

Make the IDE Compile→SignAndroidPackage flow generate the typemap, without regressing the normal outer/inner RID split or the deferred-registration correctness that motivated the outer-only gate. Options:

• Allow _GenerateTrimmableTypeMap to run in the inner build when no outer build produced the list (guard on !Exists($(_TypeMapAssembliesListFile))), ensuring it still has the inputs it needs; or
• Ensure the IDE/BuildingInsideVisualStudio flow performs the RID-less outer typemap generation before SignAndroidPackage; or
• Replace the hard Error with on-demand generation in this flow.

Acceptance criteria

• DesignTimeBuildSignAndroidPackage(NativeAOT) passes.
• Normal dotnet build (single + multi-RID) typemap generation unchanged.
• Deferred-registration propagation correctness preserved.

References

• Repro test: DesignTimeBuildSignAndroidPackage (src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs).
• Code: src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets (_GenerateTrimmableTypeMap line ~81, _ReadGeneratedTrimmableTypeMapAssemblies line ~169).