[thomhurst]

Fixes #7104

Root cause

In the [MethodDataSource] branch of TestDataAnalyzer, each unwrapped data type is checked against its test parameter type with HasImplicitConversionOrGenericParameter. When the parameter is a bare ITypeParameterSymbol, that helper skips the normal conversion check (IsGenericDefinition() is true). It then falls through to compilation.HasImplicitConversion(int, T), which is false for an unconstrained T. So every generic method with a type-parameter parameter (<T1, T2>(T1, T2) with tuple rows, <T>(T) with single rows, with or without [GenerateGenericTest]) got TUnit0001. The single-parameter shortcut further down had the same problem, so <T>(T) hit the final catch-all report even once the zip check passed.

The [Arguments] path (CanConvert) already returns true early for a type-parameter target.

Fix

• New CompilationExtensions.CanBindToTestParameter(argument, parameter). A bare type-parameter target accepts any data type, because the type argument is inferred from the data or supplied by [GenerateGenericTest]. Other targets fall back to the existing HasImplicitConversionOrGenericParameter.
• Real mismatches are still reported when the analyzer can be sure of them. The data type has to satisfy the type parameter's class, struct (not Nullable<T>), unmanaged and new() constraints, and any constraint type that does not mention type parameters (through an identity, implicit reference or boxing conversion; user-defined conversions don't count). Self-referencing constraints such as where T : IComparable<T> are checked with the data type substituted for T; constraints mentioning other type parameters are skipped. A Nullable<T> data type never satisfies a constraint type. This mirrors how the source generator validates its statically inferred type arguments, since rows that fail there are silently dropped. If the declaring method or type has [GenerateGenericTest], constraints are not checked, because the type argument comes from the attribute and the data converts to it.
• Only the two [MethodDataSource] call sites (the per-parameter zip and the single-parameter shortcut) use the new helper. UnwrapTypes still uses the strict helper on purpose. Otherwise a single T parameter would match the wrapper type (IEnumerable<Func<int>>) before it is unwrapped, and checks such as the Func mutability warning would be skipped.
• Concrete parameters are unaffected. For example, (int, string) into <T>(T, int) is still flagged.

Tests

New tests in tests/TUnit.Analyzers.Tests/MethodDataSourceAnalyzerTests.cs:

• Not flagged: tuple rows into <T1, T2> with and without [GenerateGenericTest]; Func<int> and plain int rows into <T>; mixed <T>(T, string); satisfied struct, IComparable constraint; self-referencing IComparable<T> constraint.
• Still flagged: concrete mismatch in a generic method <T>(T, int); where T : struct with string; where T : class with int; where T : IDisposable with int; where T : new() with string.

Without the analyzer change, the 7 not-flagged tests fail and the 5 still-flagged tests pass.

TUnit.Analyzers.Tests, full suite, Release: net8.0, net9.0 and net10.0 each 851 passed, 0 failed, 1 skipped (that skip is already on main).

Notes

• The #pragma warning disable TUnit0001 that fix(engine): align reflection-mode data sources and hooks with source-gen #7094 adds in tests/TUnit.TestProject/Bugs/_7092/GenerateGenericTestTupleInferenceTests.cs is not on main yet, so this PR has nothing to remove. It can be dropped once both PRs are in.
• The source-gen discovery gap for <T>(T) with non-tuple rows is a generator bug, tracked separately in Source-gen: generic test method with a non-tuple [MethodDataSource] is not discovered #7108.

Summary by CodeRabbit

• Bug Fixes
  • Improved validation of data supplied to generic tests, including tuple and scalar values, mixed generic and concrete parameters, and generated generic tests.
  • Data compatibility checks now account for generic parameter constraints, including reference, value, unmanaged, interface, and parameterless-constructor requirements. Nullable value types that do not satisfy an interface constraint are rejected, and incompatible data continues to produce a diagnostic.
  • Open or unresolved data types and runtime conversion cases are handled without misleading incompatibility errors.

[chatgpt-codex-connector]

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📝 Walkthrough

The MethodDataSource analyzer now infers generic type arguments from data-source types and checks whether each argument can bind to its test parameter. The checks include applicable generic constraints. Added tests cover compatible and incompatible data, generated generic tests, and repeated type parameters.

Changes: Generic MethodDataSource Binding

Layer / File(s)	Summary
Type inference and substitution src/TUnit.Analyzers/Extensions/CompilationExtensions.cs	Added type-argument inference, uncertainty handling, generated generic-test detection, and recursive type substitution.
Generic parameter binding rules src/TUnit.Analyzers/Extensions/CompilationExtensions.cs	Added CanBindToTestParameter and checks for generic constraints, including reference, value, unmanaged, constructor, and resolvable type constraints.
Analyzer integration and validation src/TUnit.Analyzers/TestDataAnalyzer.cs, tests/TUnit.Analyzers.Tests/MethodDataSourceAnalyzerTests.cs	The analyzer uses the new inference and binding checks. Tests cover compatible data and mismatches involving concrete parameters, generated types, repeated parameters, and constraints.

Priority: ➖ Normal

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

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to a4512

This change narrows TUnit0001 so it stops flagging valid generic MethodDataSource tests while still reporting real mismatches. The analyzer's constraint checks match how tests are generated by default, so the change should not hide errors or flag valid tests. It is ready to merge.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Linked Issues check		Issue #7104 is addressed for the reported method-level cases. CheckMethodDataSource now calls CanBindToTestParameter for the per-parameter check and the single-parameter shortcut. The helper also …	Make HasGenerateGenericTestAttribute recognize [GenerateGenericTest] on the applicable declaring method or containing type. Add an analyzer test with the attribute on the containing type and a method-declared type parameter.
Docstring Coverage		Docstring coverage is 10.81% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 37 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the analyzer fix, the TUnit0001 false positive, and the affected MethodDataSource scenario involving generic type-parameter parameters.
Out of Scope Changes check		The production changes implement [MethodDataSource] binding for generic parameters, constraint checks, generated generic test handling, and preservation of concrete mismatch diagnostics. The added t…

Full details: Out of Scope Changes check

Explanation

The production changes implement [MethodDataSource] binding for generic parameters, constraint checks, generated generic test handling, and preservation of concrete mismatch diagnostics. The added tests cover these behaviors. The changes remain within issue #7104. The separate source-generator discovery gap remains explicitly out of scope.

Full details: Linked Issues check

Explanation

Issue #7104 is addressed for the reported method-level cases. CheckMethodDataSource now calls CanBindToTestParameter for the per-parameter check and the single-parameter shortcut. The helper also preserves concrete mismatches and checks applicable constraints. However, HasGenerateGenericTestAttribute selects typeParameter.DeclaringMethod before typeParameter.DeclaringType. A method-declared type parameter therefore ignores [GenerateGenericTest] on its containing type. The current tests do not establish support for this required method-or-type case.

Resolution

Make HasGenerateGenericTestAttribute recognize [GenerateGenericTest] on the applicable declaring method or containing type. Add an analyzer test with the attribute on the containing type and a method-declared type parameter.

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[github-actions]

Review of #7109

The fix is sound. It targets the root cause: a bare type-parameter target never passed HasImplicitConversion. CanBindToTestParameter mirrors the [Arguments] path and keeps the strict check in UnwrapTypes, with a good explanation of why. The constraint checks are conservative: they skip constraints that mention type parameters, accept open or error types, and exempt [GenerateGenericTest]. The new tests cover both the not-flagged and still-flagged directions. I traced the logic by reading it and did not run the tests.

Minor points, none blocking:

• CompilationExtensions.cs: the new XML doc comment follows directly after the previous method's closing brace. Add a blank line.
• HasGenerateGenericTestAttribute only inspects the method or type that declares the type parameter. That matches how the attribute is applied, but a one-line comment saying so would help. Matching on Name plus namespace string is also fine, but a cached GetTypeByMetadataName lookup would be more robust than repeated ToDisplayString() allocations in the analyzer. This is a small cost on a non-hot path.
• Consider adding tests for a class-level generic (class MyClass<T>) and for where T : unmanaged and notnull. notnull is currently unhandled, so a nullable reference type argument is accepted. That is lenient and safe.

Approve from my side.

[chatgpt-codex-connector]

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Actionable comments posted: 1

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Inline comments:
Review comments at @src/TUnit.Analyzers/Extensions/CompilationExtensions.cs:
- Around line 83-86: In the generic argument constraint check around the
`argumentType` guard, accept non-value, non-sealed types before evaluating
constraints, since runtime values may satisfy constraints despite a broader
static type. Keep the existing type-parameter, error-type, dynamic, and
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Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no new actionable issues remain.

Summary

Fixes false TUnit0001 errors for bare generic parameters supplied by MethodDataSource.

• Method data now binds to generic test parameters without false type errors.

Previous threads were unnumbered, so no numbered finding entries are required. The boxed-row finding was withdrawn after thomhurst explained the generator's declared-type inference. Current code addresses the numeric-string, repeated-parameter, and registered-converter findings. thomhurst explicitly accepted that unconvertible data with GenerateGenericTest may fail at run time rather than produce a build error, because declared types cannot predict every conversion supported by CastHelper.

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[github-actions]

Review of #7109

The fix targets the root cause. A bare type-parameter target now binds in the two [MethodDataSource] sites, and UnwrapTypes stays strict on purpose. The tests cover both sides: 7 cases that must not be flagged and 5 or more that must still be flagged. I did not run the tests myself.

Suggestions, none of them blocking:

1. Constraint checking is a lot of new analyzer logic for a bug fix. SubstituteTypeParameter, ContainsTypeParameter and the constraint walk reimplement part of the C# constraint rules. The PR says this mirrors the source generator's validation. If both can use one shared helper, they cannot drift apart. If they can't, put a comment in both places that points to the other. Otherwise a false positive (analyzer errors, generator accepts) or a false negative will be hard to track down.
2. Bias toward not reporting. A false TUnit0001 on valid code is worse than a missed diagnostic. The default: return null in the substitution (skip the constraint) follows that. Consider also adding tests for these shapes:
   • array data into new()
   • an abstract class into new()
   • a where T : unmanaged case
   • a constraint like where T : IEnumerable<T>
3. Cosmetic: there is no blank line between the end of HasImplicitConversionOrGenericParameter and the new /// <summary> in CompilationExtensions.cs.
4. Minor: HasGenerateGenericTestAttribute checks only the declaring method or type of the type parameter. That matches the described semantics. It also compares the attribute's namespace as a string on every call. This is cheap here, but you could use GetTypeByMetadataName if the check ever moves to a hot path.

Overall this is a solid, well-tested fix. Approving in spirit.

[github-actions]

Review of #7109 (TUnit0001 false positive for generic [MethodDataSource])

I read the diff but didn't build it or run the tests. The skill-based review tool errored, so this is a manual read.

The root cause and fix look right. A bare ITypeParameterSymbol target went through HasImplicitConversionOrGenericParameter and then HasImplicitConversion(int, T), which is always false. CanBindToTestParameter now matches the [Arguments] path (CanConvert), which already accepts a type-parameter target. The [GenerateGenericTest] handling is sensible: the data must convert to each supplied type argument. The single-parameter shortcut is fixed as well, and the test matrix is thorough.

Main concern: size and maintenance.

• About 280 lines of constraint-checking and type-substitution logic now sit in the analyzer: SubstituteTypeParameters, InferExactTypeArguments, IsExactType, and checks for class, struct, unmanaged, new() and constraint types.
• This duplicates what the compiler and the source generator already know. Every bug in it is a false positive in the user's build, which is the failure TUnit0001 false positive: [MethodDataSource] on a generic test method with type-parameter parameters #7104 reported.
• A smaller design would treat a bare type-parameter target as always bindable, matching CanConvert. If you still want a safety net, check only the cheap and certain constraints (class/struct, and non-generic constraint types) and drop InferExactTypeArguments and the substitution machinery. Most of the diagnostic value would remain at a fraction of the risk.
• If you keep the full version, consider moving it to its own file, such as GenericConstraintChecker. CompilationExtensions is a poor home for it. The CanSatisfyConstraints / SubstituteTypeParameters / ContainsTypeParameter helpers are unit-testable on their own.

Smaller points:

• SubstituteTypeParameters returns null for shapes it doesn't handle, such as pointers and nested generic containers, and the caller then skips the constraint. That is the right failure mode (skip, don't report). A short comment saying so would help the next reader.
• GetGenerateGenericTestTypeArguments matches the attribute by name and namespace string. That is fine for an analyzer, but check that it stays in sync if the attribute is ever renamed or moved.
• HasPublicParameterlessConstructor treats a struct as always satisfying new(), which is correct. It also returns false for an abstract class, which matches the compiler.

No blocking issues. I'd approve, with the simplification above as a suggestion.

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Review comments at @src/TUnit.Analyzers/Extensions/CompilationExtensions.cs:
- Around line 79-112: Update InferExactTypeArguments to expose which type
parameters have conflicting exact bindings instead of keeping that information
local and discarded. In the per-parameter binding check, reject arguments whose
bare type parameter is marked conflicting, so repeated parameters with different
exact argument types report a mismatch.

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[github-actions]

Review of PR 7109. The fix targets the right place: a bare type-parameter test parameter no longer produces TUnit0001, and only the two MethodDataSource call sites use the new helper, so UnwrapTypes keeps its strict check. The tests cover both the removed false positives and the mismatches that are still reported. I only read the diff and did not build or run the tests. The code-review skill failed to run, so this is a manual review. Concern 1, scope: about 280 lines of constraint-solving logic (type substitution, exact-type inference, class/struct/unmanaged/new() checks) now live in CompilationExtensions. This duplicates C# constraint rules and the source generator's validation, and a false positive is costlier in an analyzer than a missed diagnostic. A smaller design would accept any bare T and keep only the cheap, certain checks (class/struct and concrete constraint types), or move the logic into a dedicated, separately tested checker class. Concern 2, drift: the doc comment says this mirrors the source generator, but nothing enforces it. Name the source of truth or add a shared test. Concern 3, repeated work: GetGenerateGenericTestTypeArguments re-reads attributes for every parameter on every row, so cache it per method in CheckMethodDataSource. Nit: add a blank line before the summary of CanBindToTestParameter. Verdict: behavior looks correct and the tests are good. I would simplify or isolate the constraint logic, but I don't consider it blocking.

[github-actions]

Review of #7109

The fix addresses the root cause correctly. A bare type-parameter target is now accepted at both [MethodDataSource] call sites, and UnwrapTypes deliberately keeps the strict check. The tests cover both the not-flagged and still-flagged cases. I only read the diff and did not build or run the tests.

Concerns

1. The analyzer now carries a lot of logic for a rule that should stay conservative. The issue is a false positive, but the PR adds about 300 lines to CompilationExtensions. They include constraint checking, type substitution, InferExactTypeArguments, and a model of CastHelper runtime conversion (IsRuntimeConvertible, CanConvertToGeneratedTypeArguments). A diagnostic is worth emitting only if it is almost never wrong. Mirroring the runtime conversion rules in an analyzer is brittle, because it has to be kept in sync with CastHelper by hand. Any drift will bring back false positives, which is the bug this PR fixes. A smaller alternative is for CanBindToTestParameter to return true for any type-parameter target, and for the [GenerateGenericTest] case to skip checking entirely. The PR keeps only the cheap, unambiguous constraint checks: class, struct, unmanaged, new(). The [GenerateGenericTest] conversion modelling and the substitution and inference machinery would go. If the extra reporting is wanted, it could go in a follow-up with tests tied to CastHelper behaviour.

2. Duplicated knowledge with the source generator. The PR description says this mirrors the generator's validation of type arguments. Two independent implementations of the same constraint rules will drift. Consider sharing one helper, for example a linked source file used by both the analyzer and the generator, if the rules must match.

3. Perf in the analyzer hot path. IsRuntimeConvertible calls GetTypeByMetadataName and walks AllInterfaces on every check. GetGenerateGenericTestTypeArguments re-reads the attributes for every parameter. For large test projects, resolve the well-known types once, for example in RegisterCompilationStartAction. GetGenerateGenericTestTypeArguments could also be computed once per method.

4. Unrelated change in the test file. A UTF-8 BOM was added to the first line of MethodDataSourceAnalyzerTests.cs. It is noise in the diff, so please revert it.

5. Test gaps. Consider adding:

   • a type-level [GenerateGenericTest] case;
   • a case where the same T appears in two parameters with conflicting data types;
   • a nullable-value-type data case, which the code handles explicitly.

None of these is a blocker. The behaviour looks correct for the cases tested. I'd still prefer simplifying toward the conservative option in point 1 over keeping the full conversion model.