[TrimmableTypeMap] Implement alias support in codegen and runtime

[simonrozsival]

Summary

Implements trimmable typemap alias support end-to-end, covering both generated metadata/code and runtime lookup/activation.

Fixes #11103
Part of #10788

Changes

New: IJavaPeerAliases interface (JavaPeerProxy.cs)

• string[] Aliases { get; } — lists the exact TypeMap keys for an alias group

Build-time (ModelBuilder + Emitter)

For alias groups (≥2 .NET types sharing a JNI name, e.g., JavaCollection / JavaCollection<T>):

• Generates an alias holder class extending JavaPeerProxy + IJavaPeerAliases
• Base JNI name entry → alias holder (self-referencing trim target)
• Each type gets [0]-based indexed entry: "jni/Name[0]", "jni/Name[1]", ...
• TypeMapAssociation links each type to the alias holder (keeps holder alive when any alias survives trimming)
• TargetType / CreateInstance throw NotSupportedException (alias holder is never used for peer creation)
• Also adds self-application (AddCustomAttribute on typeDefHandle) for all proxy types — required for GetCustomAttribute<JavaPeerProxy>() to work at runtime

Runtime (TrimmableTypeMap.cs)

• GetProxyForManagedType(): if (proxy is IJavaPeerAliases aliases) → iterate exact keys from Aliases property
• GetAllTypesForJniName(): detect alias holder, enumerate listed keys
• ActivateInstance(): same alias holder detection
• Zero cost for non-alias types — single is check that's false, no dictionary probing

Generated output for an alias group

// TypeMap entries:
[assembly: TypeMap<Object>("some/JavaType", typeof(JavaType_Aliases), typeof(JavaType_Aliases))]
[assembly: TypeMap<Object>("some/JavaType[0]", typeof(A_Proxy), typeof(A))]
[assembly: TypeMap<Object>("some/JavaType[1]", typeof(B_Proxy), typeof(B))]

// Keep alias holder alive when any alias type survives trimming:
[assembly: TypeMapAssociation<Object>(typeof(A), typeof(JavaType_Aliases))]
[assembly: TypeMapAssociation<Object>(typeof(B), typeof(JavaType_Aliases))]

// Alias holder — IS a JavaPeerProxy, implements IJavaPeerAliases:
[JavaType_Aliases]
class JavaType_Aliases : JavaPeerProxy, IJavaPeerAliases
{
    public override Type TargetType => throw new NotSupportedException();
    public override IJavaPeerable? CreateInstance(...) => throw new NotSupportedException();
    public string[] Aliases => new[] { "some/JavaType[0]", "some/JavaType[1]" };
}

Tests

331 passing (+9 new):

• 3 alias fixture types (3-way alias group mirroring JavaCollection/JavaCollection<T> pattern)
• Model builder tests for alias holders, 3-way aliases, mixed activation
• Fixture scanner tests verifying alias detection from real assemblies
• Integration test verifying alias holder class + IJavaPeerAliases in emitted PE

[Copilot]

Pull request overview

Implements end-to-end alias support for the Trimmable TypeMap pipeline (codegen + runtime), enabling multiple managed types to share a single JNI name via an alias-holder indirection and indexed alias keys.

Changes:

• Add IJavaPeerAliases and generate alias-holder proxy types + indexed TypeMap entries + TypeMapAssociation records for alias groups.
• Update runtime lookup/activation paths (TrimmableTypeMap*) to expand alias holders into their concrete alias entries.
• Add/expand unit tests and fixture types covering 2-way/3-way aliases and emission round-trips.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/TestFixtures/TestTypes.cs	Adds fixture types that intentionally share a JNI name to form a 3-way alias group.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TypeMapModelBuilderTests.cs	Updates/extends model-builder tests for indexed alias entries, alias holders, and associations.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TypeMapAssemblyGeneratorTests.cs	Adds a round-trip emission test asserting alias-related typemap artifacts are present in emitted metadata.
src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMapTypeManager.cs	Switches to enumerating all types for a JNI name (to support alias expansion).
src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs	Adds alias-aware type enumeration and alias resolution for proxy lookup and activation.
src/Mono.Android/Java.Interop/JavaPeerProxy.cs	Introduces IJavaPeerAliases used by generated alias-holder proxy types.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyEmitter.cs	Emits alias-holder types and self-applies proxy/holder attributes for AOT-safe GetCustomAttribute instantiation.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/ModelBuilder.cs	Generates alias holders, base-entry indirection, indexed alias keys, and associations for duplicate JNI-name groups.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/Model/TypeMapAssemblyData.cs	Extends the model to carry alias-holder emission data.

[simonrozsival]

/review

[github-actions]

✅ Android PR Reviewer completed successfully!

[github-actions]

⚠️ Needs Verification

The alias support implementation is well-structured — the JavaPeerAliasesAttribute / alias holder pattern cleanly separates alias groups from the fast non-alias path, and the runtime handles both paths correctly with appropriate caching.

Summary

Severity	Count
⚠️ Warning	2
💡 Suggestion	3

Key findings

1. ⚠️ Fragile handle resolution — EmitJavaPeerAliasesAttribute re-derives the TypeDefinitionHandle from GetRowCount instead of using the handle returned by AddTypeDefinition. Capture and pass it explicitly.

2. ⚠️ UCO/callback boolean encoding unified — EncodeClrTypeForCallback was removed, and callback MemberRefs now use the same byte encoding as UCO wrappers. Previous tests specifically verified that callbacks used sbyte for boolean to match MCW n_* method signatures. Needs confirmation that the MCW signatures were also updated.

3. 💡 Generic alias matching — GetProxyForJniClass uses exact Type equality for alias groups, which misses open generic → closed generic matches. The fallback path handles this correctly, but generic aliases always take the slower path.

Positive callouts

• Clean separation of alias holders from proxy types — alias holders extend Object (not JavaPeerProxy), keeping GetCustomAttribute<JavaPeerProxy>() as a zero-cost filter for non-alias entries.
• Good test coverage: model builder tests, assembly generator tests, and fixture-based alias tests all verify the new codegen.
• The self-application fix (using MethodDefinitionHandle instead of MemberReferenceHandle for the proxy's own custom attribute) is a nice improvement.
• Thorough OnRegisterNatives update to register natives for ALL proxies in an alias group, not just the first.

Note on scope

This PR also includes significant TestRunner infrastructure changes (removing DryRun, NoExclusions, changing filter/count mechanics) that appear orthogonal to the trimmable typemap alias feature. Consider splitting those into a separate PR for cleaner review history.

Generated by Android PR Reviewer for issue #11122 · ● 21.1M

[simonrozsival]

Test failure unrelated (Mono.Android.NET_Tests-Interpreter)

[jonathanpeppers]

👍