Fix main build broken by csproj-based MSTest packaging (#9259)

[Evangelink]

Problem

main is broken: the latest CI builds fail in the Build/Test tasks (Windows/Linux/macOS). The failures came in layers — fixing each revealed the next. This PR fixes all of them.

#	Stage	Symptom	Root cause
1	Restore	NU1605 downgrade of Microsoft.Testing.Platform.MSBuild	#9259: adapter flows the locally-built platform MSBuild transitively, conflicting with the darc-pinned PackageReference
2	Compile	CS0234 missing MSTestAdapter.PlatformServices types	#9259: adapter sets PrivateAssets="all" on PlatformServices, hiding it from in-repo consumers
3	AfterSolutionBuild	verify-nupkgs.ps1 file-count mismatch for MSTest.AotReflection.SourceGeneration	#9338 made the PoC packable; not added to the expected-counts table
4	Test (acceptance)	AnalyzersShouldBeEnabled*, MSTEST0001/0014, AnalyzerMessagesShouldBeLocalized, VerifyMSTestAnalysisMode*	#9259: MSTest.TestFramework was packed with empty dependency groups — the MSTest.Analyzers dependency was dropped, so analyzers no longer ran for consumers
5	Restore	NU1608 Roslyn version conflict in the source-generation unit tests	fixing #4 made the analyzer projects' Microsoft.CodeAnalysis.* refs leak transitively through the framework, clashing with the pinned Roslyn 3.11.0

The xlf drift that originally broke main was already fixed by #9339.

Fixes

• test/Directory.Build.targets — under UseMSTestFromSource, reference Microsoft.Testing.Platform.MSBuild from source so both references resolve to the same version. (NU1605)
• MSTest.IntegrationTests / MSTestAdapter.UnitTests — add a direct ProjectReference to MSTestAdapter.PlatformServices. (CS0234)
• eng/verify-nupkgs.ps1 — add MSTest.AotReflection.SourceGeneration = 6. (verify-nupkgs)
• TestFramework.Extensions.csproj — remove ReferenceOutputAssembly="false" from the MSTest.Analyzers.Package reference so pack emits <dependency id="MSTest.Analyzers" include="...Analyzers,BuildTransitive" /> at the co-built version. (analyzers)
• MSTest.Analyzers / MSTest.Analyzers.CodeFixes — mark Microsoft.CodeAnalysis.* references PrivateAssets="all" so Roslyn (a compiler-host-provided dependency) never flows to consumers. (NU1608)

The adapter's intentional PrivateAssets settings are unchanged — the produced packages keep their historical dependency graphs.

Validation

• Reproduced each failure on clean main (/p:OfficialBuildId=20260622.12, so the build version exceeds the darc pin) and confirmed each fix resolves it.
• Built all affected projects (integration/adapter/source-gen/analyzer unit tests) — restore + build with 0 errors; the two source-gen test projects restore without NU1608.
• Analyzers: packed MSTest.TestFramework + MSTest.Analyzers, built a consumer referencing the package → warning MSTEST0014 fires again. The MSTest.Analyzers package still ships all analyzer assemblies with zero dependencies; the framework net462 build stays clean with analyzers active.

Refs #9259, #9338.

[Copilot]

Pull request overview

Fixes the main branch build break caused by the csproj-based MSTest.TestAdapter packaging changes (#9259) by aligning in-repo test project references with the new PrivateAssets behavior and avoiding a restore-time NU1605 downgrade scenario when UseMSTestFromSource=true.

Changes:

• Add direct ProjectReference to MSTestAdapter.PlatformServices for test projects that compile against its types, since it no longer flows transitively from MSTest.TestAdapter due to PrivateAssets="all".
• Replace a Microsoft.Testing.Platform.MSBuild PackageReference with a source ProjectReference when UseMSTestFromSource=true to eliminate restore downgrades against the locally-built MSBuild integration.
• Document the rationale inline in the affected project files / targets.

Show a summary per file

File	Description
test/UnitTests/MSTestAdapter.UnitTests/MSTestAdapter.UnitTests.csproj	Adds direct reference to MSTestAdapter.PlatformServices so unit tests can compile against its APIs despite PrivateAssets="all" on the adapter’s reference.
test/IntegrationTests/MSTest.IntegrationTests/MSTest.IntegrationTests.csproj	Adds direct reference to MSTestAdapter.PlatformServices to restore compile-time access for integration test code using those types.
test/Directory.Build.targets	Switches Microsoft.Testing.Platform.MSBuild from PackageReference to ProjectReference under UseMSTestFromSource=true to prevent NU1605 downgrade vs the transitively-referenced source-built project.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0

[Evangelink]

Note

🤖 Automated review by GitHub Copilot. Posted via a maintainer's GitHub token, so it appears under their account — the account owner did not write or approve this content personally. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 22/22 dimensions clean — no findings.

Review notes (all dimensions)

Scope: 3 MSBuild project files changed (test/Directory.Build.targets, MSTest.IntegrationTests.csproj, MSTestAdapter.UnitTests.csproj). No C# runtime code touched.

Dimension	Result	Notes
1. Algorithmic Correctness	✅ LGTM	Fix correctly targets the root cause: PrivateAssets="all" on the MSTestAdapter.PlatformServices ProjectReference in MSTest.TestAdapter prevents the assembly from flowing as a compile-time reference to consumers. Adding direct ProjectReference entries in both consuming test projects restores the reference. The PackageReference→ProjectReference change in Directory.Build.targets correctly resolves the NU1605 downgrade by ensuring both the direct reference and the transitively-flowed one resolve to the same locally-built project version.
2. Threading & Concurrency	N/A	No C# code changed.
3. Security & IPC Contract Safety	N/A	Build config changes only.
4. Public API & Binary Compatibility	N/A	No public API touched.
5. Performance & Allocations	N/A	No runtime code changed.
6. Cross-TFM Compatibility	✅ LGTM	MSTestAdapter.PlatformServices is built for all TFMs that MSTestAdapter.UnitTests targets (net462;net48;net8.0;net9.0;WinUiMinimum), because MSTest.TestAdapter already includes them all. The single-TFM MSTest.IntegrationTests ($(NetFrameworkMinimum)) is also covered.
7. Resource & IDisposable Management	N/A	No code changed.
8. Defensive Coding at Boundaries	N/A	No code changed.
9. Localization & Resources	N/A	No strings changed.
10. Test Isolation	N/A	No test code changed.
11. Assertion Quality	N/A	No test code changed.
12. Flakiness Patterns	N/A	No test code changed.
13. Test Completeness & Coverage	✅ LGTM	This is a build/restore fix with no new code paths; the author validated by reproducing the failure with /p:OfficialBuildId=20260622.12 and confirming all 6 affected projects restore and build clean. No additional tests needed.
14. Data-Driven Test Coverage	N/A	No test code changed.
15. Code Structure & Simplification	N/A	No C# code changed.
16. Naming & Conventions	N/A	No C# code changed.
17. Documentation Accuracy	✅ LGTM	All three added XML comments accurately explain why the reference is needed (link to #9259, explain the PrivateAssets="all" mechanism). Comments describe the intent, not just what the element does.
18. Analyzer & Code Fix Quality	N/A	No src/Analyzers/ files changed.
19. IPC Wire Compatibility	N/A	No serialization code changed.
20. Build Infrastructure & Dependencies	✅ LGTM	The PackageReference→ProjectReference swap is gated on UseMSTestFromSource='true' (matching the old condition), sits inside the existing EnableMSTestRunner OR UseInternalTestFramework outer ItemGroup, and references a first-party in-repo project that is always resolvable. The direct ProjectReference entries in the two test projects do not duplicate the assembly in output since MSBuild deduplicates project builds. InternalsVisibleTo coverage confirmed: MSTestAdapter.PlatformServices.csproj already declares InternalsVisibleTo for both Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests and MSTest.IntegrationTests. The four other UseMSTestFromSource=true projects omitted from the fix (MSTest.VstestConsoleWrapper.IntegrationTests, MSTest.Analyzers.UnitTests, MSTest.AotReflection.SourceGeneration.UnitTests, MSTest.SelfRealExamples.UnitTests) do not consume MSTestAdapter.PlatformServices internals directly and are not listed in its InternalsVisibleTo; they build fine without an explicit reference.
21. Scope & PR Discipline	✅ LGTM	Single, tightly-scoped concern. Clear description with root-cause analysis, precise reproduction steps, and explicit validation. Refs #9259 appropriately.
22. PowerShell Scripting Hygiene	N/A	No .ps1 files changed.
MSBuild Authoring (supplemental)	✅ LGTM	Condition quoting is consistent with the repo style ('$(Prop)' == 'value'). The new ProjectReference has no PrivateAssets (defaults to all-assets-flow), which is the correct behavior for a test project reference. No DependsOn append issues, no stray whitespace, no condition ordering problems.

[Copilot]

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 7/7 changed files
• Comments generated: 1

[Evangelink]

🧪 Test quality grade — PR #9344

No new or modified test methods were identified in the changed regions
of this PR. Nothing to grade.

_{Re-run with /grade-tests.}

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