[typemap] Validate exported Java fields

[simonrozsival]

Summary

• match legacy [ExportField] initializer validation in the trimmable scanner with localized XA4205/XA4207/XA4208 diagnostics
• match Java.Interop.ExportFieldAttribute by full identity during validation, field collection, and registration parsing
• reject invalid initializer members before adding Java fields or marshal methods
• add focused build parity coverage for isolated and combined invalid initializers across LLVM-IR CoreCLR, trimmable CoreCLR, and trimmable NativeAOT
• add on-device runtime parity coverage for instance field initialization alongside the existing static field tests

Behavior

Parameterized and void [ExportField] initializers now report XA4205 and XA4208 respectively, matching LLVM-IR. Generic declaring types report XA4207 before initializer signature validation in both trimmable runtimes.

Combined-invalid coverage verifies the same diagnostic precedence: XA4205 wins for a parameterized void initializer, while XA4207 wins when that initializer is declared on a generic type.

The scanner skips invalid initializer members instead of generating invalid Java fields and marshal methods. Attribute matching now uses the full Java.Interop.ExportFieldAttribute identity so unrelated user-defined attributes with the same short name are ignored.

Validation

• 776 Microsoft.Android.Sdk.TrimmableTypeMap.Tests tests on the final head
• focused 15-case build matrix covering isolated and combined invalid shapes across three supported runtime/typemap configurations
• on-device Export coverage under LLVM-IR CoreCLR, trimmable CoreCLR, and trimmable NativeAOT
• git diff --check

Root of GitHub Stack #12627. Tracks #12561 and #11289.

[Copilot]

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Review tier: Lite
Findings: 1 · 1

New issues introduced by this change (2)

Severity	Finding
	src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​TrimmableTypeMapBuildTests.cs — ❌ error — The typemap output assertion only checks for *.TypeMap.dll, but trimmable typemap…
	src/​Microsoft.Android.Sdk.TrimmableTypeMap/​Scanner/​JavaPeerScanner.cs — 💡 suggestion — ValidateExportField() introduces an extra per-method custom-attribute scan and…

What changed in this PR

This PR tightens trimmable typemap parity with the legacy [ExportField] pipeline by validating invalid exported-field initializer shapes early (parameterized/void), emitting the corresponding XA4205/XA4208 diagnostics, and ensuring the generator stops before writing partial typemap/Java outputs. It also expands the Java-source semantic parity fixture and adds new host/device coverage for static/instance/protected exported fields.

Changes:

• Add [ExportField] signature validation in the trimmable scanner and surface XA4205/XA4208 through the shared logger/task plumbing.
• Extend generator + integration fixtures/tests to assert “no partial Java fields / marshal methods” for invalid [ExportField] shapes and to validate ordered field semantics (static/instance/protected).
• Add on-device coverage for instance primitive [ExportField] initialization visibility.

File	Description
tests/​Mono.Android-Tests/​Mono.Android-Tests/​Java.Interop/​ExportTests.cs	Adds a device test validating instance primitive exported-field initialization is visible via JNI.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.Tests/​TestFixtures/​TestTypes.cs	Introduces invalid [ExportField] fixture types (parameterized + void return) for regression testing.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.Tests/​Generator/​TrimmableTypeMapGeneratorTests.cs	Adds generator-level assertions for legacy XA4205/XA4208 diagnostics and absence of partial Java/typemap members.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.Tests/​Generator/​ExportFieldTests.cs	Adds focused unit coverage ensuring invalid export fields produce no Java field or marshal wrapper.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/​JavaSourceSemanticParityTests.cs	Extends the semantic parity fixture to cover field ordering/modifiers and adds a Java consumer for reads.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/​JavaSourceParityFixture/​JavaSourceParityTypes.cs	Adds a protected exported field to increase fixture coverage for visibility and instance fields.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​TrimmableTypeMapBuildTests.cs	Adds build-time coverage asserting invalid [ExportField] stops before writing typemap/Java outputs and matches legacy diagnostics.
src/​Xamarin.Android.Build.Tasks/​Tasks/​GenerateTrimmableTypeMap.cs	Plumbs XA4205/XA4208 into the MSBuild logger using localized Java.Interop resources.
src/​Microsoft.Android.Sdk.TrimmableTypeMap/​Scanner/​JavaPeerScanner.cs	Adds scanner-side validation to reject parameterized/void [ExportField] initializers before member emission.
src/​Microsoft.Android.Sdk.TrimmableTypeMap/​ITrimmableTypeMapLogger.cs	Extends the shared logger interface with new ExportField-specific diagnostic hooks.

[simonrozsival]

/review

[github-actions]

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Generated by Android PR Reviewer for #12596

[github-actions]

Review summary

Verdict: ⚠️ Needs changes — 0 errors, 1 warning, 0 suggestions.

The validation logic matches the measured legacy diagnostic precedence, invalid members are excluded before field/marshal-method collection, and the localized task logging is wired consistently. The remaining issue is regression coverage: the final matrix no longer exercises combined-invalid signatures, so the precedence behavior is not protected.

CI build #1576821 is still in progress with no reported failures at review time.

Generated by Android PR Reviewer for #12596 · gpt56 · 243.4 AIC · ⌖ 9 AIC · ⊞ 25.7K
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