[TrimmableTypeMap] Add TypeMap proxy groundwork with CreateInstance

[simonrozsival]

Part of #10799

Summary

Adds the core pipeline that transforms scanned JavaPeerInfo records into TypeMap .dll assemblies with proxy types and CreateInstance support.

Generator pipeline

 Input assemblies (*.dll)
│
▼
┌───────────────┐
│ JavaPeerScanner│ Scans PE metadata for [Register] types,
└───────┬───────┘ activation ctors, interfaces, base types
│
│ List
▼
┌───────────────┐
│ ModelBuilder │ Alias detection, ACW filtering, proxy naming,
└───────┬───────┘ unconditional vs trimmable classification
│
│ TypeMapAssemblyData
▼
┌──────────────────────┐
│ TypeMapAssemblyEmitter│ IL emission: proxy types, CreateInstance,
│ + PEAssemblyBuilder │ TypeMap attributes, IgnoresAccessChecksTo
└──────────┬───────────┘
│
│ PE bytes
▼
┌───────────────┐
│ Output *.dll │ _MyApp.TypeMap.dll (per-assembly)
└───────────────┘ _Microsoft.Android.TypeMaps.dll (root)

Tests

• 141 tests covering model builder, assembly generator, root assembly generator, and scanner behavior
• Test fixtures include MCW bindings, user ACW types, interfaces with invokers, nested types, generics, Implementor/EventDispatcher helpers, JI-style activation ctors, and edge cases

Future optimization

• Implementor and EventDispatcher types are currently treated as unconditional (matching legacy behavior). Trimming optimization deferred to [TrimmableTypeMap] Explore trimming optimization for Implementor and EventDispatcher types #10911.

UCO wrappers, RegisterNatives, and IAndroidCallableWrapper support will be added in follow-up PRs.

Follow-up work

• [TrimmableTypeMap] Add integration tests for generator-consumed scanner fields #10913 — Integration tests for generator-consumed scanner fields (IsUnconditional, InvokerTypeName, CompatJniName, ManagedMethodName). These are new concepts with no legacy equivalent, so they cannot be validated via legacy-vs-new comparison and need standalone correctness tests.
• [TrimmableTypeMap] Decompose _GenerateJavaStubs: shared tasks for trimmable path #10807 — Decompose _GenerateJavaStubs: shared tasks for trimmable path
• [TrimmableTypeMap] Explore trimming optimization for Implementor and EventDispatcher types #10911 — Trimming optimization for Implementor/EventDispatcher types

[jonathanpeppers]

My AI code reviewer says this, but I don't think we need to take any action except look at the yaml changes:

 PR #10808 Review Summary
Title: [TrimmableTypeMap] Add TypeMap proxy groundwork with CreateInstance
Author: @simonrozsival | +2956 / -88 across 20 files | 43 commits
What it does
Adds the core code generation pipeline that transforms scanned JavaPeerInfo records into per-assembly TypeMap .dll assemblies containing proxy types with CreateInstance methods. Pipeline: Scanner →
ModelBuilder → Emitter → PE output.
Architecture (excellent)
Clean 3-layer separation:
- ModelBuilder — all decision logic (dedup, alias detection, ACW filtering, 2-arg vs 3-arg classification). Pure data in, pure data out.
- TypeMapAssemblyEmitter — mechanical IL emission from the model. No business logic.
- PEAssemblyBuilder — shared plumbing (MetadataBuilder, assembly refs, scratch BlobBuilders, PE serialisation). Reused by both per-assembly and root generators.
Findings
┌───┬────────────┬─────────────────────────────────────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ # │ Severity │ File │ Issue │
├───┼────────────┼─────────────────────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ 1 │ Medium │ JavaPeerInfo.cs │ ManagedTypeNamespace and ManagedTypeShortName are added and populated by the scanner, but not consumed by any production code in this PR. The │
│ │ │ │ ModelBuilder and emitter don't reference them. Likely for follow-up PRs (UCO wrappers / RegisterNatives), but this is speculative code shipping │
│ │ │ │ ahead of its consumer. │
├───┼────────────┼─────────────────────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ 2 │ Low │ TypeMapAssemblyData.cs │ Contains 6 types in one file (170 lines). The types are cohesive model records, but one-type-per-file is a strict convention in this org. Could │
│ │ │ │ split into TypeMapAttributeData.cs, JavaPeerProxyData.cs, TypeRefData.cs, ActivationCtorData.cs, TypeMapAssociationData.cs. │
├───┼────────────┼─────────────────────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ 3 │ Low │ TypeMapAssemblyGeneratorTests.cs, │ Missing newline at end of file (\ No newline at end of file). │
│ │ │ TypeMapModelBuilderTests.cs │ │
└───┴────────────┴─────────────────────────────────────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
Positives
- Deterministic output: SortedDictionary for JNI name ordering, sorted aliases, content-fingerprinted MVID — builds are reproducible.
- PEAssemblyBuilder scratch BlobBuilders: Reuses _sigBlob/_codeBlob/_attrBlob per method, avoiding per-emission allocations. Correctly captures the sig blob handle before emitIL callbacks (which can call
AddMemberRef and clear _sigBlob). There's even a regression test (EmitBody_ILCallbackCallsAddMemberRef_SignatureNotCorrupted) for this.
- 141 tests covering model builder, PE generation round-trips, root assembly, scanner behavior, and edge cases (generics, nested types, aliases, JI-style ctors, invoker exclusion).
- Test infrastructure refactoring: Extracted FixtureTestBase with Lazy<> cached fixture scanning — scanner tests and generator tests share the same fixture without re-scanning.
- IL emission comments map to pseudo-C# equivalents, making the ECMA-335 byte-level code readable.
- 5 CreateInstance strategies properly handled: leaf newobj, inherited (GetUninitializedObject), invoker, JI-style (with JniObjectReference conversion + DeleteRef cleanup), generic definition (throws), and
no-activation (returns null).
Summary
This is a well-structured, well-tested foundation PR. The main substantive concern is the two unused JavaPeerInfo properties shipping without consumers. The rest is clean.