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A default-initialized Arg<T> had no matcher, so setup and verification could fail for methods with five parameters, where predicate overloads are not generated. Default arguments now use a cached exact matcher for default(T).
The fallback is stateless to avoid sharing captures between unrelated default arguments. Default capture accessors return empty values; explicitly constructed arguments keep their existing capture behavior. Regression tests cover null, zero, nullable values, mismatches, and verification through a five-parameter generated method.
Validation: dotnet test --project tests/TUnit.Mocks.Tests --framework net10.0 --no-restore passed all 1,481 tests. No generator output or public API signatures changed.
No actionable comments were generated in the recent review.
Walkthrough
Default-initialized Arg<T> instances now match default(T) without capturing values. The change also makes Values and Latest safe when no capture matcher exists. Tests cover default matching for a five-parameter setup and a default-initialized integer argument.
Changes: Default argument matching
Layer / File(s)
Summary
Default matcher and regression tests src/TUnit.Mocks/Arguments/ArgOfT.cs, tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs
Arg<T>.Matcher falls back to an exact matcher for default(T). Values returns an empty list and Latest returns default when no capture matcher exists. Tests cover a five-parameter setup and confirm that a default Arg<int> matches zero but not one.
thomhurst/TUnit#7415: Maps null predicate arguments to Arg.IsNull<T>() in generated overloads, addressing a connected argument-matching path.
Merge Risk: Minimal · up to a2c00
Default arguments match without capturing values. No merge-blocking issue was established.
Pre-merge checks: 5
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Description Check
Check skipped - CodeRabbit’s high-level summary is enabled.
Title check
The title "Fix default mock argument matching" matches the main change. The PR changes default-initialized Arg so it matches default(T) and returns empty captures, which addresses the linked issue …
Linked Issues check
Issue #7441 requires that default argument matchers are safe on setup and verification paths, and that regression coverage exists for methods without generated predicate overloads (five parameters). A…
Out of Scope Changes check
The whole-PR diff against the merge base 6bc28cd touches two files. src/TUnit.Mocks/Arguments/ArgOfT.cs changes the default-Arg matcher, capture accessors, and XML documentation that describes the de…
Docstring Coverage
No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Full details: Title check
Explanation
The title "Fix default mock argument matching" matches the main change. The PR changes default-initialized Arg<T> so it matches default(T) and returns empty captures, which addresses the linked issue about default arguments not matching null. The title is short, specific, and states the primary fix.
Full details: Linked Issues check
Explanation
Issue #7441 requires that default argument matchers are safe on setup and verification paths, and that regression coverage exists for methods without generated predicate overloads (five parameters). At the reviewed head, Arg<T>.Matcher returns _capturingMatcher ?? DefaultMatcher.Instance (src/TUnit.Mocks/Arguments/ArgOfT.cs). DefaultMatcher.Instance is new ExactMatcher<T>(default). ExactMatcher<T>.Matches uses EqualityComparer<T>.Default, so a default string? matches null, a default int matches 0, and a default int? matches null. The fallback is stateless, which avoids shared captures. Values and Latest also handle the missing capture matcher without throwing. Regression tests in tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs add the five-parameter INullLiteralService.Five method. They cover null, zero, nullable, and mismatch cases, and verify call counts through the generated method. The default-Arg capture-state test checks empty Values, Latest equal to 0, and matcher behavior. The source change addresses the issue diagnosis. I did not execute the test suite. The test result rests on the PR description and on source inspection.
Full details: Out of Scope Changes check
Explanation
The whole-PR diff against the merge base 6bc28cd touches two files. src/TUnit.Mocks/Arguments/ArgOfT.cs changes the default-Arg matcher, capture accessors, and XML documentation that describes the default behavior. tests/TUnit.Mocks.Tests/NullLiteralMatcherTests.cs adds the five-parameter test interface member and regression tests. Each change maps directly to #7441. The PR states that generator output and public API signatures are unchanged. The diff shows no unrelated changes.
Full details: Docstring Coverage
Explanation
No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 2 files.
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A rabbit checks a default value with care No capture waits, yet matching works there Zero is found, while one is not Five arguments follow the values set A quiet test confirms the lot
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No blocking issues. The change is small and correct.
Arg<T> now falls back to a cached, stateless ExactMatcher<T>(default) when _capturingMatcher is null. That fixes setup and verification for five-parameter methods, which have no predicate overloads.
The shared matcher is held in a nested static class inside the generic struct, so there is one instance per T. It carries no capture state, so unrelated default arguments cannot interfere with each other.
Values and Latest now return empty results on a default Arg<T> instead of throwing a NullReferenceException.
The ExactMatcher constructor's Arg<>-boxing guard does not fire for default, since the value is null or default(T).
The tests cover null, zero, nullable values, mismatches, and verification through a five-parameter method, plus the empty capture state.
Minor, non-blocking: a default Arg<T> silently exposes empty Values, so a user who writes Arg<int> a = default; and later reads a.Values gets an empty list with no hint about why. The XML doc now says this, which is enough.
Approve from my side.
I did not run the tests. I only read the diff and ExactMatcher.
Marked ready at unchanged head a2c008f after positive current-head Claude and Codex verdicts; all review surfaces are clear. Claude ready-for-review run 42100184523 is queued. Auto-merge must wait until that run passes and its new comment is read, per repository merge guidance. CI also starts on promotion.
The fix is small and correct. A default Arg<T> now falls back to a cached ExactMatcher<T>(default). Its Values and Latest return empty or default values instead of throwing a NullReferenceException.
The nested static class holds one matcher per closed T. It has no mutable state, so default args can't share captures. The ExactMatcher constructor's boxed-Arg guard doesn't trigger for default.
The tests cover null, zero, nullable, mismatch and verification through a five-parameter method, plus the empty capture state.
Optional points:
A user who reads .Values on a default Arg gets a silently empty list, which could hide a mistake. The XML doc now says this, which is enough.
Array.Empty<T?>() is allocation-free. Good.
No blocking issues. I haven't run the tests myself.
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A default-initialized
Arg<T>had no matcher, so setup and verification could fail for methods with five parameters, where predicate overloads are not generated. Default arguments now use a cached exact matcher fordefault(T).The fallback is stateless to avoid sharing captures between unrelated default arguments. Default capture accessors return empty values; explicitly constructed arguments keep their existing capture behavior. Regression tests cover null, zero, nullable values, mismatches, and verification through a five-parameter generated method.
Validation:
dotnet test --project tests/TUnit.Mocks.Tests --framework net10.0 --no-restorepassed all 1,481 tests. No generator output or public API signatures changed.Closes #7441
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