Part of #10788
Details outlined in #10757
Implementation Plan
Implement a build-time code generation step that runs before the trimmer and produces:
- Per-assembly typemap assemblies — one per input assembly containing Java peer types, plus a root `_Microsoft.Android.TypeMaps.dll` that ties them together via `TypeMapAssemblyTargetAttribute`
- JCW Java source files (`.java`) with `registerNatives` in `static {}` blocks
Uses System.Reflection.Metadata (SRM) for both reading and emitting — no Mono.Cecil.
Key design decisions
| Decision |
Choice |
| Assembly reading/writing |
SRM only, no Cecil |
| Marshal method registration |
`RegisterNatives` (no LLVM IR) |
| Access to protected members |
`IgnoresAccessChecksTo` |
| Incremental builds |
Per-assembly typemap assemblies via `TypeMapAssemblyTargetAttribute` |
| TypeMap entries |
`TypeMapAttribute` 2-arg (unconditional) and 3-arg (trimmable) |
| Proxy pattern |
Self-application: `[Proxy] class Proxy : JavaPeerProxyAttribute` |
| JCW Java stubs |
`registerNatives` in `static {}`, actual JNI package names (no CRC hash) |
| Task assembly |
Separate `Microsoft.Android.Build.TypeMap` project (fast inner dev loop) |
Architecture: Separate task assembly
New project `src/Microsoft.Android.Build.TypeMap/` (`netstandard2.0`) keeps the scanner, generators, and MSBuild task in a dedicated assembly separate from `Xamarin.Android.Build.Tasks`. This enables a fast inner dev loop (~5s build+test) without building the full solution.
Incremental builds: Per-assembly typemap generation
Mono.Android.dll ──→ _Mono.Android.TypeMap.dll (only rebuilt when Mono.Android changes)
AndroidX.Core.dll ──→ _AndroidX.Core.TypeMap.dll (only rebuilt when NuGet updates)
MyApp.dll ──→ _MyApp.TypeMap.dll (rebuilt on every app code change)
──→ _Microsoft.Android.TypeMaps.dll (root: TypeMapAssemblyTarget refs + aliases)
Typical incremental build cost: <0.5s (only re-scan the app assembly + regenerate root).
Testing strategy
- Side-by-side legacy comparison: Run legacy `XAJavaTypeScanner` + `TypeMapCecilAdapter` (Cecil) and new `JavaPeerScanner` (SRM) on the same assemblies, compare results
- Hand-crafted test assembly (~20 types) for TDD inner loop (<1s)
- Real Mono.Android.dll (~8000 types) smoke test (~5s)
- Integration tests in existing `Xamarin.Android.Build.Tests` project
References
Part of #10788
Details outlined in #10757
Implementation Plan
Implement a build-time code generation step that runs before the trimmer and produces:
Uses System.Reflection.Metadata (SRM) for both reading and emitting — no Mono.Cecil.
Key design decisions
Architecture: Separate task assembly
New project `src/Microsoft.Android.Build.TypeMap/` (`netstandard2.0`) keeps the scanner, generators, and MSBuild task in a dedicated assembly separate from `Xamarin.Android.Build.Tasks`. This enables a fast inner dev loop (~5s build+test) without building the full solution.
Incremental builds: Per-assembly typemap generation
Typical incremental build cost: <0.5s (only re-scan the app assembly + regenerate root).
Testing strategy
References