Use Array.Empty in source generated code to reduce allocations

[thomhurst]

No description provided.

[claude]

Claude finished @thomhurst's task —— View job

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Code Review Complete ✅

Reviewing PR #3139: "Use Array.Empty in source generated code to reduce allocations"

Summary

This PR implements a performance optimization by replacing new T[] { } with Array.Empty<T>() in source-generated code. The change affects 98 files, primarily test snapshot files, with core implementation changes in TestMetadataGenerator.cs and MetadataGenerationHelper.cs.

Code Quality & Best Practices ⭐

Excellent implementation that follows .NET performance best practices:

✅ Proper use of Array.Empty<T>(): This is the recommended pattern for empty arrays in .NET
✅ Consistent application: All empty array instantiations have been systematically replaced
✅ Maintains code readability: The generated code remains clear and understandable
✅ Follows TUnit's performance-first philosophy: Aligns with CLAUDE.md requirement that "Performance is paramount"

Performance Considerations ⚡

Significant positive impact:

✅ Allocation reduction: Array.Empty<T>() returns a singleton empty array, eliminating repeated allocations
✅ Memory efficiency: Reduces GC pressure by reusing the same empty array instance
✅ Hot path optimization: These arrays are created frequently during test discovery/execution
✅ Runtime performance: Faster instantiation since no new memory allocation is needed

Estimated impact: For a large test suite with thousands of tests, this could save considerable memory and reduce GC overhead.

Potential Bugs or Issues ✅

No issues found:

✅ Behavioral equivalence: Array.Empty<T>() and new T[] { } are functionally identical
✅ Type safety preserved: All generic type constraints remain intact
✅ Thread safety: Array.Empty<T>() is thread-safe and immutable
✅ Compatibility: Works across all supported .NET versions (.NET Standard 2.0+)

Security Concerns ✅

No security implications: This is a pure performance optimization with no security impact.

Test Coverage 📋

Comprehensive test coverage:

✅ Snapshot tests updated: All 88 test snapshot files have been properly updated
✅ Generated code validated: The test snapshots demonstrate the change works correctly across all scenarios
✅ Behavioral parity maintained: Source-generated and reflection modes continue to behave identically

Note: The massive diff (3,436 deletions, 1,235 additions) is primarily due to snapshot test updates, which is expected and proper.

Implementation Quality 🏗️

Well-executed changes:

✅ Centralized in helpers: Changes properly implemented in CodeGenerationHelpers and MetadataGenerationHelper
✅ Consistent patterns: All empty array scenarios handled uniformly
✅ Proper use of global qualified names: global::System.Array.Empty<T>() prevents naming conflicts

Areas of Excellence

1. Systematic approach: The change was applied consistently across all empty array scenarios
2. Performance awareness: Demonstrates understanding of .NET memory allocation patterns
3. Test discipline: Proper acceptance of all snapshot changes
4. Code generation best practices: Uses fully qualified type names to avoid conflicts

Recommendations

✅ Ready to merge: This is a clean, beneficial performance optimization with no downsides.

Final Assessment

This PR represents a textbook example of a well-executed performance optimization. It follows .NET best practices, maintains behavioral equivalence, and provides measurable performance benefits without introducing any risks. The systematic application across the entire codebase and proper test snapshot updates demonstrate thorough engineering discipline.

Verdict: Strongly recommend approval 🚀

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