perf(source-gen): resolve parameter reflection info through a shared runtime helper

[thomhurst]

Summary

Generated code emitted one lambda per test, hook and constructor parameter to resolve its ParameterInfo lazily:

ParameterMetadataFactory.Create(typeof(int), "value", ..., false,
    reflectionInfoFactory: static () => typeof(X).GetMethod("M", BindingFlags..., null, new Type[] { ... }, null)!.GetParameters()[0])

TUnit.TestProject had 1,205 of these. Each one adds a closure method, a cached delegate field and IL, and each parameter repeated the same method lookup.

This PR removes the lambdas. The parameter array is now wrapped in a call to a shared runtime helper that resolves the ParameterInfos once per method, lazily:

ParameterMetadataFactory.ForMethod(typeof(X), "M", false, new ParameterMetadata[]
{
    ParameterMetadataFactory.Create(typeof(int), "value", ..., false),
    ...
})

What changed

• TUnit.Core: adds ParameterMetadataFactory.ForMethod, ForGenericMethod and ForConstructor (all EditorBrowsable(Never)). They attach an internal ParameterInfoResolver and an index to each ParameterMetadata. On the first ReflectionInfo access, the resolver looks the method up once, using the parameters' own Types, and caches the ParameterInfo[] for every parameter of that method. ReflectionInfoFactory still takes precedence, so existing callers behave as before.
• The lookup rules match the old lambdas exactly:
  • Non-generic methods: GetMethod(name, Public|NonPublic|Instance-or-Static, types).
  • Generic methods, or methods whose parameters use type parameters: the first method with a matching name and parameter count.
  • Constructors: GetConstructor(types), or matching by parameter count when a parameter type uses type parameters.
  • Nested and open-generic declaring types keep the same typeof(...) expression as before.
• Trimming/AOT: the declaring-type parameter is annotated with [DynamicallyAccessedMembers(PublicConstructors | PublicMethods | NonPublicMethods)]. MethodMetadata.Type and ClassMetadata.Type already require the same members for these types, so nothing extra is rooted.
• Generator: MetadataGenerationHelper emits the wrapper and plain Create(...) calls. The unused SourceInformationWriter.GenerateMembers / GenerateParameterInformation path was the only single-parameter caller, so it is removed.
• The reflection still runs lazily, on first ReflectionInfo access, never at startup.
• One small behavior change: if a lookup fails on the exact-type path, you now get the existing InvalidOperationException ("ReflectionInfo ... was not set") instead of a NullReferenceException.

Measurements

TUnit.TestProject, net10.0 Release, same worktree, origin/main vs this branch.

Metric	main	this PR	Change
reflectionInfoFactory lambdas in generated code	1,205	0	-1,205
TUnit.Core.SourceGenerator output (1,580 files)	9,273,266 B	8,959,893 B	-313 KB (-3.4%)
TUnit.TestProject.dll	6,294,528 B	6,126,592 B	-168 KB (-2.7%)
ILC trim/AOT warnings (dotnet publish -p:Aot=true, analysis phase)	62	62 (identical set)	0

CoreCompile and startup (--list-tests) were measured in 3 interleaved rounds, but the machine was heavily loaded by concurrent builds. CoreCompile samples ranged from 5 to 18 s on both sides, and the medians (13.1 s vs 13.7 s) are within noise. Startup CPU and wall medians were also within noise. I can't claim a measurable compile-time or startup change from this data. The measured wins are the smaller IL and generated source above, plus one reflection lookup per method instead of one per parameter when ReflectionInfo is used.

Testing done

• TUnit.Core.SourceGenerator.Tests: net10.0, net9.0 and net8.0 all pass. On net472, 1 failure (AssemblyCleanupTests, a path-too-long error from the deep worktree path, environmental). Snapshots were reviewed with a script: every changed line is a parameter-metadata emission change. Snapshots were accepted for every TFM.
• TUnit.PublicAPI: accepted the three new ParameterMetadataFactory members for all four TFMs. The remaining OpenTelemetry_Library_Has_No_API_Changes failure is the same path-length environmental issue.
• New tests/TUnit.TestProject/ParameterReflectionInfoTests.cs checks that ReflectionInfo resolves the right name, position, type and member for constructor parameters, instance methods, params arrays, generic methods, nested classes and a static method (through the factory). It also checks that parameters of one method share the resolved member.
• Targeted TestProject runs in both source-generated and reflection modes: the new tests, MatrixTests, GenericMatrixTests, MixedMatrixTests, MatrixExclusionBugTest, CombinedDataSourceTests, ArgsAsArrayTests, GenericMethodTests, Bugs/_2136 and Bugs/_4431. All pass except:
  • CompositionPatternDoesNotWork_4431: expected failure ([EngineTest(ExpectedResult.Failure)]).
  • ClassArgumentsTests: fails identically on main.
• TUnit.Core builds with 0 trim analyzer warnings (it is IsAotCompatible on net8+). The AOT publish of TestProject gives the same 62 ILC warnings as main; linking can't complete locally because there is no MSVC linker.

Summary by CodeRabbit

• New Features
  • Parameter metadata now supports reflection details for constructors, regular methods, and generic methods, including parameter names, types, positions, and owning members.
• Bug Fixes
  • Improved parameter information lookup, including for generic methods and constructors.

[chatgpt-codex-connector]

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📝 Code Review	✅ Completed 2026-09-29T08:37:00.066917Z	ae6cf5f	New commits

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Reviewing files that changed from the base of the PR and between 115f7fc and ae6cf5f.

📒 Files selected for processing (3)

• src/TUnit.Core/Models/TestModels/ParameterMetadata.cs
• src/TUnit.Core/ParameterMetadataFactory.cs
• tests/TUnit.TestProject/ParameterReflectionInfoTests.cs

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📒 Files selected for processing (94)

• src/TUnit.Core.SourceGenerator/CodeGenerators/Writers/SourceInformationWriter.cs
• src/TUnit.Core.SourceGenerator/Utilities/MetadataGenerationHelper.cs
• src/TUnit.Core/Models/TestModels/ParameterMetadata.cs
• src/TUnit.Core/ParameterMetadataFactory.cs
• tests/TUnit.Core.SourceGenerator.Tests/ArgsAsArrayTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ArgumentWithImplicitConverterTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/AssemblyAfterTests.Test.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/AsyncMethodDataSourceDrivenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ClassAndMethodArgumentsTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ClassConstructorTest.Test.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/ClassDataSourceDrivenTests2.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ClassDataSourceDrivenTestsSharedKeyed.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ClassTupleDataSourceDrivenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.DataDrivenTest_WithConflictingNamespace.DotNet10_0.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.DataDrivenTest_WithConflictingNamespace.DotNet8_0.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.DataDrivenTest_WithConflictingNamespace.DotNet9_0.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.DataDrivenTest_WithConflictingNamespace.Net4_7.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.HooksTest_WithConflictingNamespace.DotNet10_0.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.HooksTest_WithConflictingNamespace.Net4_7.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.MatrixTest_WithConflictingNamespace.DotNet10_0.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/ConflictingNamespaceTests.TupleDataSource_WithConflictingNamespace.DotNet10_0.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/MethodDataSourceDrivenWithCancellationTokenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/MultipleClassDataSourceDrivenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/NameOfArgumentTests.Test.verified.txt
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• tests/TUnit.Core.SourceGenerator.Tests/TimeoutCancellationTokenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/TupleDataSourceDrivenTests.Test.verified.txt
• tests/TUnit.Core.SourceGenerator.Tests/UnifiedReflectionFreeTests.Test_AotSafeDataSourceFactories.verified.txt
• tests/TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet10_0.verified.txt
• tests/TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet8_0.verified.txt
• tests/TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.DotNet9_0.verified.txt
• tests/TUnit.PublicAPI/Tests.Core_Library_Has_No_API_Changes.Net4_7.verified.txt
• tests/TUnit.TestProject/ParameterReflectionInfoTests.cs

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---

📝 Walkthrough

Walkthrough

The source generator now emits shared reflection resolvers for method and constructor parameter metadata. ParameterMetadata uses a resolver as a fallback for reflection information. Generated snapshots and tests cover the new factory calls and parameter details.

Changes

Parameter reflection metadata

Layer / File(s)	Summary
Shared resolver and parameter factories src/TUnit.Core/ParameterMetadataFactory.cs, src/TUnit.Core/Models/TestModels/ParameterMetadata.cs	The factory adds helpers for methods, generic methods, and constructors. Each helper attaches a shared resolver and a parameter index. ReflectionInfo uses the resolver after its existing factory returns no value.
Generator output and verified snapshots src/TUnit.Core.SourceGenerator/Utilities/MetadataGenerationHelper.cs, src/TUnit.Core.SourceGenerator/CodeGenerators/Writers/SourceInformationWriter.cs, tests/TUnit.Core.SourceGenerator.Tests/*.verified.txt	Generated method and constructor parameter arrays use the shared factories instead of per-parameter reflection callbacks. The writer removes three metadata-generation methods. Several generated snapshots also remove their leading UTF-8 BOM.
API baselines and reflection tests tests/TUnit.PublicAPI/*.verified.txt, tests/TUnit.TestProject/ParameterReflectionInfoTests.cs	The public API snapshots record the added factory methods. New tests check parameter names, positions, types, and reflected members across constructors, methods, generic methods, params arrays, and nested types.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant GeneratedCode
  participant ParameterMetadataFactory
  participant ParameterMetadata
  GeneratedCode->>ParameterMetadataFactory: Create metadata with ForMethod or ForConstructor
  ParameterMetadataFactory->>ParameterMetadata: Attach shared resolver and index
  ParameterMetadata->>ParameterMetadataFactory: Resolve parameter on ReflectionInfo access
  ParameterMetadataFactory-->>ParameterMetadata: Return cached reflection parameter

Loading

Merge Risk: ⚪ Minimal · up to 115f7

No actionable issue remains that should delay merging. Normal checks can proceed.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 115f7

The normal generated path appears to preserve the previous reflection lookup behavior. The new public helpers do create a conditional risk of associating a parameter with the wrong reflection metadata if callers reuse or mutate the supplied array. No new security bypass is established.

Retained concerns

• Low · reliability · inferred: The public factories return the caller's mutable array while the lazy resolver retains it and assigns each entry an index. If a caller reorders or replaces entries before lookup, or reattaches entries after some have resolved, entries can expose reflection metadata for a different parameter or member. The fresh, ordered arrays emitted by the generator do not demonstrate this failure.

Security review details

Security Blast Radius

• inferred — The new direct-call surface is available to core-package consumers, while generated callers supply compile-time types and method names. The inspected path establishes metadata lookup within the caller's process, not an external attacker entrypoint.

Trust Boundaries and Controls

• observed — ParameterMetadata preserves explicitly supplied ReflectionInfoFactory precedence, and the generated factory calls use literal method names and compile-time declaring types. No bypass of an authentication or authorization control was established in this path.

Resilience and Maintainability Implications

• inferred — Incorrect parameter association under caller mutation could affect reflection-based attribute discovery where cached attributes are unavailable. The inspected evidence does not establish that such discovery enforces a security boundary.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 36.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 25 functions across 5 files. (89 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: resolving parameter reflection information through a shared runtime helper in source-generated code. It is concise and relevant.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 36.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 25 functions across 5 files. (89 skipped: 89 unsupported.)

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Commit to this branch
• Create a new PR

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

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_{A rabbit checks each parameter’s name,
Its position and type in the same.
A shared resolver finds the right place,
Then caches the result with care and grace.
The test snapshots follow the trace.}

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[github-actions]

Review of #6923

I read the runtime side of this PR: ParameterMetadataFactory, ParameterInfoResolver and the ParameterMetadata.ReflectionInfo change. I did not run the build or tests, and I did not inspect the generator changes or the snapshot diffs. The automated code-review skill failed to run, so this is a manual pass.

The design is sound. One shared lazy lookup per method replaces N closures, which removes the per-parameter delegate fields and repeated GetMethod calls. ReflectionInfoFactory still takes precedence, so existing callers are unaffected. The DynamicallyAccessedMembers annotations on the declaring type keep the trimming story intact. The public API snapshots are updated for the new EditorBrowsable(Never) methods.

Minor suggestions, none blocking:

1. Cached failure: Resolve() returns [] when the lookup fails, and _resolved caches it. Every parameter then throws the generic "ReflectionInfo ... was not set" InvalidOperationException. That message hides the real cause, which is that the method or constructor lookup found nothing. Including the declaring type, the method name and the lookup kind in the exception would make debugging much easier. The old lambdas would have thrown a NullReferenceException from !, so this is already an improvement. It would still be worth doing.
2. Thread safety: _resolved ??= Resolve() can run Resolve twice under a race. That is harmless because the result is idempotent, but a short comment saying so would help. Most callers hit this from parallel test execution.
3. Generated-code contract: Attach mutates the passed-in ParameterMetadata instances and relies on each array being used for one method only. That holds for generated code today. A note in the XML docs would stop someone from reusing an array across methods later, since the last resolver would win.
4. Test coverage: ParameterReflectionInfoTests covers the new paths. I would add explicit cases for a static method, a constructor matched by parameter count (open generic declaring type), and a generic method with overloads of the same arity. FindByParameterCount returns the first match, as the old lambdas did, but overloads of the same arity make that ordering-sensitive.

Overall this is a good change, and I have no blocking concerns.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Refactors parameter reflection lookup from inline to shared runtime helper.

The PR appears safe to merge; no actionable new issue was identified.

Summary

The PR replaces generated per-parameter reflection lambdas with a shared, lazy resolver for each method or constructor and updates snapshots and tests accordingly.

• The changes since the previous review clarify lookup failures and same-arity overload behavior, and add focused resolver tests.

_{Reviews (2) · Last reviewed commit: "perf(source-gen): address review feedbac..."}

[thomhurst]

Re-measured on an idle machine (no other builds running). tests/TUnit.TestProject, net10.0 Release, warm compiler server, CoreCompile after touching one file; 2 rounds x 8 warm runs per branch (first 6 runs after each generator swap discarded as warm-up).

	median	min
main	2668 ms	2594 ms
this PR	2484 ms	2397 ms

About -7% CoreCompile.

[github-actions]

Review: shared lazy ParameterInfo resolver

I couldn't run the automated code-review skill (it errored), so this is a manual read of the diff. I didn't build or run any tests.

Verdict: looks good.

• Replacing about 1,200 per-parameter lambdas with one resolver per method cuts generated IL and closure fields. It also removes the repeated GetMethod lookups, since each method is now resolved once and the ParameterInfo[] is shared.
• ReflectionInfo still checks ReflectionInfoFactory first, so existing callers keep their behaviour. A failed lookup throws a descriptive InvalidOperationException via Describe(), and the old ! null-forgiving crash is gone.
• The benign race in Get is fine: the lookup is idempotent and the reference assignment is atomic.
• The DynamicallyAccessedMembers annotations sit on the factory parameters and the resolver field, which keeps the AOT/trimming story intact.

Minor points, none blocking:

1. Attach mutates the passed-in ParameterMetadata instances and binds each to its array index. The remarks document this, but a reordered or shared array would silently return the wrong ParameterInfo. Consider a cheap Debug-only sanity check, for example asserting that the resolved parameter's Name equals Name, so a mismatch fails loudly.
2. ForMethod/ForConstructor keep the type-based matching that the old lambdas used. ForGenericMethod matches the first overload with the same name and parameter count, as before. That is the same known ambiguity as the old code, so no regression, just worth a test for same-arity generic overloads if one doesn't exist.
3. The .verified.txt diffs also drop the UTF-8 BOM on the first line. Please confirm that comes from the generator output and not from an editor. If it's intentional, ignore this.

Nice cleanup.

🤖 Generated with Claude Code