Fix source generator crash on null DataRow arguments

[Sergio Pedri (Sergio0694)]

Summary

Fixes the NullReferenceException from MSTestReflectionMetadataGenerator when an attribute argument is a null array, including [DataRow(null)]. Roslyn exposes a default ImmutableArray for these arguments, so enumerating TypedConstant.Values crashes the generator.

• Short-circuit null arrays without enumerating their values, while checking accessibility of array element types used in generated casts and literals.
• Match the unit-test DataRowAttribute stub to the real constructor overloads so null binds to the array overload instead of masking the bug.
• Cover positional and named null arrays, nested arrays, inaccessible element types, and materialization as exactly one null argument.
• Extend managed and Native AOT acceptance tests to verify the null row executes exactly once.
• Make Windows crash-dump setup create the WER LocalDumps registry key when the hosted agent image does not provide it, allowing the build to proceed.

Minimal reproducer (no linked GitHub issue was provided):

[TestMethod]
[DataRow(null)]
public void AcceptsNull(string? value) => Assert.IsNull(value);

Validation

• All 170 source-generator unit tests passed.
• Managed source-generation acceptance test passed on net10.0.
• Native AOT acceptance test passed on net10.0 / win-x64, including publishing with both MSBuild and compiler warnings treated as errors. No IL warning suppressions were added.
• Re-ran MSTest.SourceGeneration.UnitTests after review: build and tests succeeded with 0 warnings and 0 errors.
• Confirmed the Windows CI failure occurs before compilation on main and unrelated PRs when the LocalDumps registry key is absent; the setup script now creates it idempotently.

[Copilot]

🟡 Changes recommended

The source file lacks its required BOM, and inaccessible null-array casts need direct regression coverage.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Fixes source-generator crashes when Roslyn represents null array attribute arguments with a default ImmutableArray.

Changes:

• Safely handles null arrays while validating element accessibility.
• Expands unit coverage and aligns the DataRowAttribute stub.
• Verifies managed and Native AOT execution.

Review coverage

Generator logic, overload fidelity, regression tests, acceptance paths, and file encoding.

File summaries

File	Description
AttributeMaterializationHelper.cs	Handles null array constants safely.
MSTestReflectionMetadataGeneratorTests.cs	Adds null-array materialization tests.
SourceGenerationNonAotTests.cs	Verifies managed execution.
NativeAotTests.cs	Verifies Native AOT execution.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Copilot]

🟢 Approval recommended

The focused fix is consistent with Roslyn typed-constant behavior and has comprehensive regression coverage.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[github-actions]

Final test-triage resolution — Azure Pipelines build 1602053

This is a final analysis of the completed build (all legs finished). No open issue needed.

Test results: Across all reported CTRF/TRX/JUnit records (32,661 total: 32,086 passed, 575 skipped), there were zero failed or retried tests. No flaky, crashed, or slow-regression signatures were identified (failureOrRetryCount: 0, diagnosticCount: 0, slowRegressionCount: 0), and evidence collection was complete (evidenceIncomplete: false).

Why the build shows failed: The Windows Debug and Windows Release legs ended in failed state, but the associated timeline issues are all build/pipeline-infrastructure errors, not test failures:

• Enable local dumps task failed (PowerShell exited with code 1) on both Windows legs.
• Subsequent Gather logs for publish to artifacts / Publish pipeline artifacts / Publish logs steps failed with "Path does not exist" / "Not found SourceFolder" errors for artifacts\log and artifacts, consistent with the crash-dump setup failure preventing expected output folders from being created.
• No crash dumps were produced (CrashDumps directories reported empty on both legs) and diagnostics.json is empty, so this isn't a test crash — it's the dump-enablement/log-publish tooling itself failing early in the job.

This category of failure belongs to build/pipeline infrastructure analysis rather than test triage, so I'm not creating an issue from this agent. If it recurs across unrelated PRs/commits, it would warrant a separate infrastructure investigation (Build Failure Analysis) into the "Enable local dumps" step on the Windows legs.

Conclusion: No actionable test regression, flake, or slowness found. Test suite is effectively clean for this revision.

🤖 Automated content by GitHub Copilot. Generated by the Pipeline Test Triage workflow. · copilot · auto · 48.4 AIC · ⌖ 6.37 AIC · ⊞ 8.9K

[Copilot]

🟢 Approval recommended

The fix is focused, preserves generated semantics, and has comprehensive regression coverage.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Amaury Levé (Evangelink)]

Note

🤖 Automated review by GitHub Copilot. To request a follow-up action, reply by tagging @copilot directly.

Review result: no actionable findings

The null-array handling is correctly ordered: TypedConstant.Values is no longer enumerated for null arrays, while the emitted cast's element type is still checked for accessibility. The updated DataRowAttribute stub matches the shipped overload set, and the tests verify generated-source compilation, exact one-null-argument materialization, nested arrays, named arguments, and inaccessible element types. Managed and Native AOT acceptance coverage also verifies that the row executes exactly once.

I independently built and ran MSTest.SourceGeneration.UnitTests at f9406bd0b340030e5da2d3b1a7f62a1fc1ec7e66; the project completed with 0 warnings and 0 errors. The current Windows CI failures occur in the pre-build Enable local dumps setup step because the LocalDumps registry path is absent; they are not caused by this diff.

Review coverage

• Scope and description alignment: clean; all four changed files support the stated fix.
• Algorithm and Roslyn typed-constant semantics: null, typed null, boxed null, nested array, empty array, and named-argument paths checked.
• Generated-code compatibility: emitted casts/literals, constructor overload binding, and inaccessible-type fallback checked.
• Public API and package compatibility: no public API or package metadata changes.
• Cross-TFM/AOT behavior: generator remains netstandard2.0; managed and Native AOT consumer paths covered.
• Test quality: assertions exercise compilation, emitted text, runtime materialization, discovery count, filter count, and exit code; no parallel-state or timing hazards introduced.
• Security, concurrency, resources, localization, CLI, MSBuild, and dependencies: no changed boundary or applicable regression.
• Existing review threads: both prior findings are resolved and were not duplicated.

[Copilot]

🟢 Approval recommended

The fix is focused and comprehensively validates generation, compilation, materialization, and execution paths.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Balanced