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Source-gen: generic test class does not infer its type arguments from a class-level [MethodDataSource]; reflection does #7333
Description
What happens
A generic test class whose only type information is a class-level [MethodDataSource] runs in reflection mode, but source-gen mode emits no test for it. Nothing is reported: the test is missing from the run.
public static class Sources
{
public static IEnumerable<int> Ints() => [3];
}
[MethodDataSource(typeof(Sources), nameof(Sources.Ints))]
public class ExternalNoMethodRows<T>(T a)
{
[Test]
public void Test() { _ = a; }
}
[MethodDataSource(nameof(Ints))]
public class OwnNoMethodRows<T>(T a)
{
public static IEnumerable<int> Ints() => [3];
[Test]
public void Test() { _ = a; }
}Added to tests/TUnit.TestProject and run with --treenode-filter "/*/<namespace>/<class>/*":
| Class | source-gen | --reflection |
|---|---|---|
ExternalNoMethodRows |
0 tests | 1 passed (T = int) |
OwnNoMethodRows |
0 tests | 1 passed (T = int, after the fix for #7208) |
A class-level [MethodDataSource] whose declared rows name the class's own type parameter (IEnumerable<T> Values()), with nothing else that supplies T, also emits nothing in source-gen. Reflection reports a failed test that explains the problem.
Where
TestMetadataGenerator infers a generic class's type arguments from class-level [Arguments] rows and typed class data sources (InferTypesFromTypedDataSourceForClass), but not from a class-level [MethodDataSource]. Reflection (ReflectionTestDataCollector.GroupClassRowsByTypeArgumentsAsync) reads the source's rows and groups them by the type of their values.
Expected
Both modes behave the same. For example, source-gen infers the class type arguments from the declared row type of the class-level [MethodDataSource] member, as it already does for method-level [MethodDataSource] members. If it cannot infer them, it reports a diagnostic or a failed test instead of silently emitting nothing.
Found while working on #7208.
Activity
thomhurst commentedon Nov 1, 2026
Another case of this gap, found while fixing #7336. A
[GenerateGenericTest]instantiation that class[Arguments]rows also infer, with method rows that infer the class type:Source-gen runs one test, with
value = 1. TheValues()row (5) never runs. Reflection runs two, with values 1 and 5, after #7336. The repro istests/TUnit.TestProject/Bugs/_7208/OwnClassTypeParameterMethodDataSourceWithArgumentsAndGenerateGenericTest.Issue7208Testsasserts each mode's count, so a fix here must update that test's source-gen expectation to 2.thomhurst commentedon Nov 1, 2026
Update: #7336 (bc1b447) fixes the
[GenerateGenericTest]+ class[Arguments]+ method rows case I added to this issue earlier. Source-gen now reads the own-class member on that instantiation, as reflection does. What remains here is what the body describes: source-gen doesn't infer a generic class's type arguments from a class-level[MethodDataSource], so a class whose types only that source supplies emits no test.thomhurst commentedon Nov 1, 2026
A related case came up while fixing a Codex finding on #7336. When class
[Arguments]rows already supply the types, source-gen still drops the rows of a class-level[MethodDataSource]:Reflection groups both rows into
C<int>and runs 2 tests. In source-gen, a concrete own-class member joins theC<int>instantiation only when a class-level[GenerateGenericTest(typeof(int))]also names it, throughGetOwnClassMethodDataSourcesForInstantiationinTestMetadataGenerator(#7336). Without that attribute, only the[Arguments]row runs, according to the generator code; I haven't run this exact class. Fixing #7333 should cover this case as well.fix(generator): omit unmatched class method source instantiations (#7333
fix(generator): preserve method rows and polymorphic class partitioni…
fix(generator): preserve array and nullable class source inference (#…
fix(discovery): infer nullable array constructor rows consistently (#…
fix(discovery): retain null row filtering and typed construction (#7333)
fix(discovery): guard only columns that infer class types (#7333)
fix(discovery): preserve class source factories and constructors (#7333)
7 remaining items
fix(generator): retain grouped explicit class-row filtering (#7333)
fix(generator): retain explicit null-only class rows (#7333)
fix: preserve actual generic class row groups for #7333
Fix filtering of inferred sources outside runtime partitions (#7333)
fix(generator): preserve unmatched class Arguments fallback (#7333)
fix(generator): preserve inferred constructors for grouped rows (#7333)
fix: group explicit class rows with method data sources (#7333)
fix: report class source constraints only for actual rows (#7333)
fix: retain invalid external tuple row shape (#7333)
Fix inferred empty class source skip placeholders (#7333)
Correct successful TRX summary expectations (#7333)
thomhurst commentedon Nov 3, 2026
Validation while implementing #7443 on main at 07a554f: the existing
_7208fixtures run 43 tests in both modes. Source-generated discovery has 39 passes and four type-inference failures; reflection has 42 passes and one intentional discovery failure. The three additional generated-mode failures remain within this issue’s class-level MethodDataSource inference scope.