Skip [AssemblyFixtureProvider] under Native AOT + add MSTEST0072 analyzer

[Evangelink]

Summary

[AssemblyFixtureProvider] cross-assembly discovery walks the runtime assembly reference graph (Assembly.GetReferencedAssemblies() + load-by-name via AssemblyLoadContext). That is fundamentally a reflection/runtime-loading mechanism and cannot be made reflection-free by the source generator. Under Native AOT it also surfaced an IL2026 — the last MSTest-owned trim/AOT warning a consumer hit when publishing a Native AOT test app with MSTestSourceGenMode=ReflectionFree and warnings-as-errors.

Rather than paper over it with a suppression, this PR makes the behavior explicit: skip the feature when dynamic code is unsupported, and surface it both at build time (analyzer) and at run time (trace warning).

Changes

1. Skip discovery when dynamic code is unsupported (TypeCache.ProviderDiscovery.cs)
Guard DiscoverFixturesFromProviders on RuntimeFeature.IsDynamicCodeSupported. Because ILC constant-folds that switch to false under AOT, the guarded reflection path is statically removed — so the IL2026 disappears with no suppression needed (same pattern already used in DataSerializationHelper).

2. Best-effort runtime warning
When discovery is skipped, emit a trace warning so consumers are not silently deprived of their fixtures. It scans the already-loaded assemblies (AppDomain.GetAssemblies, metadata-only via CustomAttributeData, with per-assembly failure isolation) — it deliberately does not walk the reference graph, so it stays AOT-safe. Consequently it can only see markers on assemblies that happen to be loaded (e.g. a self-applied marker on the test assembly); an unloaded referenced provider is not detectable at run time AOT-safely. Referenced providers are instead covered at build time by the analyzer. The warning is emitted through MTP's diagnostic logger (--diagnostic output).

3. New analyzer MSTEST0072 — AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzer
Warns at build time when the project opts into an AOT flavor detectable at build time — PublishAot (Native AOT) or RunAOTCompilation (Blazor WebAssembly AOT) — and [AssemblyFixtureProvider] is in play. It inspects both the compilation's own assembly attributes (reported at the attribute location) and referenced assemblies' attributes (reported as a no-location diagnostic), so the documented default usage — the attribute placed on a referenced fixture library consumed by an AOT test project — is covered. PublishAot and RunAOTCompilation are exposed to analyzers via new CompilerVisibleProperty entries in MSTest.TestAdapter.targets. Includes resources (+ regenerated xlf for all 13 locales), AnalyzerReleases.Unshipped.md entry, and unit tests (including the referenced-assembly and RunAOTCompilation scenarios).

4. Acceptance test — AssemblyFixtureProviderNativeAotTests verifies that under PublishAot=true (which sets IsDynamicCodeSupported=false for a managed build) the referenced provider's AssemblyInitialize/AssemblyCleanup are skipped while the test still passes.

Notes

• Analyzer coverage. MSTEST0072 detects [AssemblyFixtureProvider] whether it is declared in the compilation being built or on a referenced library, and it triggers on both build-time-detectable AOT flavors (PublishAot, RunAOTCompilation). The only case it cannot cover is a runtime that disables dynamic code without either build property being set (e.g. Mono iOS AOT), where there is no build-time signal to key off; the best-effort runtime trace warning is the fallback there, limited to already-loaded assemblies as described in change Porting latest changes. #2.
• Supersedes the earlier suppression-based commit on this branch.

Validation

• dotnet build of the adapter (net8.0) and MSTest.Analyzers → 0 errors (release-tracking analyzer satisfied).
• New analyzer unit tests (7, incl. referenced-assembly and RunAOTCompilation cases) pass on net8.0.
• Downstream: with discovery skipped under AOT, the reflection-free Native AOT publish reaches native codegen with no MSTest-owned IL20xx/IL30xx warnings.

[Copilot]

Pull request overview

Suppresses the IL2026 trim/AOT warning from assembly fixture provider discovery while extending acceptance-test coverage.

Changes:

• Isolates and suppresses Assembly.GetReferencedAssemblies().
• Adds the source file to trim/AOT warning assertions.

Show a summary per file

File	Description
TypeCache.ProviderDiscovery.cs	Adds the scoped IL2026 suppression helper.
TrimAndAotAssertions.cs	Guards against future trim/AOT warnings from provider discovery.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 21/21 changed files
• Comments generated: 2
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 21/21 changed files
• Comments generated: 8
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 2
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 2
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 2
• Review effort level: Medium

[github-actions]

🧪 Test quality grade — PR #9941

Grade	Test	Notes
B (80–89)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenNotPublishAot_ AttributeOnReferencedAssembly_ NoDiagnostic	Strong negative assertion via RunAsync(); body is ~45 lines due to multi-project string literals — consider extracting shared setup into a helper to reduce per-test size.
B (80–89)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenPublishAotAndAttributeOnReferencedAssembly_ Diagnostic	Good use of WithNoLocation() for cross-assembly diagnostic; body is ~45 lines — extracting the multi-project scaffolding into a shared helper would improve readability.
A (90–100)	new AssemblyFixtureProviderNativeAotTests. AssemblyFixtureProvider_ WhenDynamicCodeUnsupported_ IsSkipped	Clear AAA; rich assertions: exit code, summary, and positive and negative output checks all verified.
A (90–100)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenNotPublishAot_ NoDiagnostic	Concise, focused negative test; canonical Roslyn markup assertion pattern. No issues found.
A (90–100)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenPublishAotAndAttributeIsUsed_ Diagnostic	Clean single-scenario test with precise location-aware diagnostic assertion. No issues found.
A (90–100)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenPublishAotAndAttributeNotUsed_ NoDiagnostic	Well-scoped negative test; verifies silence when the attribute is absent under AOT. No issues found.
A (90–100)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenPublishAotAndAttributeUsedMultipleTimes_ DiagnosticOnEach	Verifies per-usage diagnostic with two independent markers; correctly tests the each-occurrence contract. No issues found.
A (90–100)	new AssemblyFixtureProviderNotSupportedWithNativeAotAnalyzerTests. WhenRunAOTCompilationAndAttributeIsUsed_ Diagnostic	Correctly tests the RunAOTCompilation property path (distinct from PublishAot); canonical markup assertion. No issues found.

_{This advisory comment was generated automatically. Grades are heuristic
and informational — they do not block merging. Re-run with
/grade-tests.}

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