refactor: remove unreachable decimal source-text path from GenerateAttributeInstantiation

[thomhurst]

Follow-up to the review on #6855, which flagged that CodeGenerationHelpers.GenerateAttributeInstantiation has its own decimal-literal source-text logic. That logic blindly applies TrimEnd(...) + "m" to any non-string, non-identifier expression, unlike the stricter TryGetDecimalLiteralText added in #6855.

Finding

The duplicated logic is unreachable. parameterTypes is only set when a caller passes targetParameters, and none of the four callers do:

• CodeGenerationHelpers.cs (attribute dictionary generation)
• StaticPropertyInitializationGenerator.cs
• TestMetadataGenerator.cs (two [MethodDataSource] fallbacks)

So isDecimalType was always false, and every argument already went through TypedConstantParser.GetRawTypedConstantValue. The invalid-C# scenario from the review cannot happen today. It would only appear if someone later wired targetParameters up.

Change

• Remove the unused targetParameters parameter and all decimal source-text branches.
• Stop fetching and parsing ApplicationSyntaxReference in this method, because only the dead branches used it.
• Keep the existing behavior: a params array expands into individual arguments, and every other argument is formatted from its typed constant.

TestMetadataGenerator.TryGetDecimalLiteralText is now the only implementation of the decision between source text and typed constant. It has one call site, so it stays private instead of moving to a shared helper.

Validation

• TUnit.Core.SourceGenerator builds with 0 warnings.
• TUnit.Core.SourceGenerator.Tests (net10.0): 155 passed, 1 skipped (pre-existing), 0 snapshot diffs. The generated output is unchanged.

Summary by CodeRabbit

• Refactor
  • Simplified generated test code for attribute instantiation by passing constructor arguments through directly.
  • Attribute arguments supplied through parameter arrays are no longer expanded into individual values.
  • Decimal attribute literals no longer receive an additional suffix during generation.
  • Removed reliance on target-parameter metadata when processing attribute arguments.

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📝 Code Review	✅ Completed 2026-09-22T20:16:22.223652Z	66c64fd	New commits

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📝 Walkthrough

Walkthrough

The source generator simplifies GenerateAttributeInstantiation. The method now accepts only AttributeData and passes constructor arguments directly through typed-constant parsing. Syntax-based value reconstruction and params-array expansion were removed.

Changes

Attribute instantiation

Layer / File(s)	Summary
Simplify attribute generation src/TUnit.Core.SourceGenerator/CodeGenerationHelpers.cs	GenerateAttributeInstantiation no longer accepts targetParameters. The method removes syntax lookup, parameter-type mapping, literal handling, decimal suffix handling, and params-array expansion. Constructor arguments use TypedConstantParser.GetRawTypedConstantValue directly.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to 66c64

No current correctness or compatibility risk was identified; the refactor is ready to merge.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately identifies the removal of the unreachable decimal source-text handling in GenerateAttributeInstantiation, which is a central change in the pull request.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
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.

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[github-actions]

Review: remove unreachable decimal source-text path from GenerateAttributeInstantiation

Verdict: LGTM. This is a clean, well-justified dead-code removal.

What I checked

• Confirmed all 4 call sites of GenerateAttributeInstantiation (TestMetadataGenerator.cs ×2, StaticPropertyInitializationGenerator.cs, and the internal recursive call in CodeGenerationHelpers.cs) never passed targetParameters — so parameterTypes was always null and the entire decimal-syntax-text branch was genuinely unreachable, matching the PR description.
• TypedConstantParser.GetRawTypedConstantValue(TypedConstant, ITypeSymbol? targetType = null) already defaults targetType to null, so the simplified call sites (GetRawTypedConstantValue(v) / GetRawTypedConstantValue(arg)) are behaviorally identical to the previous paramType-based calls, which always resolved to null anyway.
• GetNullableUnderlyingType (the extension used only by the removed branches in this file) is still used elsewhere (TypedConstantFormatter.cs), so nothing is orphaned by this cleanup.
• The now-unused using System.Collections.Immutable; and using Microsoft.CodeAnalysis.CSharp.Syntax; are correctly removed along with the syntax-reference lookup that only fed the dead branches.
• GenerateAttributeInstantiation is internal, so dropping the optional targetParameters parameter isn't a public-API break; no tests/TUnit.PublicAPI changes are needed.
• Correctly scoped to TUnit.Core.SourceGenerator only — per AGENTS.md, this metadata-collection method doesn't have a TUnit.Engine counterpart to keep in sync (execution-path code is shared), and this PR doesn't touch anything execution-related.
• TestMetadataGenerator.TryGetDecimalLiteralText (added in fix: don't request semantic models for attribute syntax from other compilations (DevKit crash) #6855) remains the sole, correctly-scoped implementation of the source-text-vs-typed-constant decision, with its single call site — keeping it private instead of extracting a shared helper is the right call per the PR description's own reasoning (no second consumer exists).

Notes

• I was unable to independently re-run dotnet build/tests in this review sandbox (command required interactive approval I don't have in this context), so I'm relying on static analysis of the diff plus the PR's stated validation (0 warnings, 155 passed/1 skipped, 0 snapshot diffs) — the logic itself checks out as equivalent by inspection.
• No architectural concerns here: this is a straightforward "delete the code path a previous review proved was unreachable" change with no new abstractions needed. The resulting method is meaningfully simpler and easier to reason about than before.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the refactor preserves existing formatting behavior and the null params-array correction matches the constructor contract.

Summary

This PR simplifies attribute-instantiation generation by removing unreachable decimal source-text handling and its unused parameter. The latest revision also preserves [Arguments(null)] semantics by emitting a null params array rather than expanding it into zero arguments.

• Removes unused syntax-reference parsing and decimal-specific branches.
• Formats ordinary constructor arguments exclusively from Roslyn typed constants.
• Continues expanding non-null params arrays into individual generated arguments.
• Emits null params arrays as a single null constructor argument.

_{Reviews (2) · Last reviewed commit: "fix: emit null for a null params array i..."}

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Actionable comments posted: 1

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Inline comments:
In `@src/TUnit.Core.SourceGenerator/CodeGenerationHelpers.cs`:
- Around line 30-37: Update the params-array expansion in the attribute argument
generation logic to add an explicit null argument when arg.Values.IsDefault is
true; retain the existing element expansion for non-default arrays so
[Arguments(null)] preserves one null constructor argument.

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[github-actions]

Review

Commit 1 (remove unreachable decimal path): Verified. All four current call sites of GenerateAttributeInstantiation (TestMetadataGenerator.cs ×2, StaticPropertyInitializationGenerator.cs, and the recursive call in CodeGenerationHelpers.cs itself) call it without targetParameters, so parameterTypes was always null and the whole decimal-syntax-text branch was dead, exactly as described. TypedConstantParser.GetRawTypedConstantValue(TypedConstant, ITypeSymbol? targetType = null) already defaults targetType to null, so GetRawTypedConstantValue(v) / GetRawTypedConstantValue(arg) are behaviorally identical to the removed paramType-based calls. Good, safe cleanup, and it's nice to see the unused ApplicationSyntaxReference/usings go with it.

Commit 2 (null params array fix) — one thing worth confirming with the author: I don't think this branch is reachable by any current caller either, which undercuts the premise a bit. Tracing where IsParamsArrayArgument (i.e. ArgumentsAttribute/InlineDataAttribute) could actually reach this function:

• GenerateTestAttributes (the only caller that iterates over arbitrary attributes) filters with !IsDataSourceAttribute(attr), and ArgumentsAttribute implements IDataSourceAttribute (src/TUnit.Core/Attributes/TestData/ArgumentsAttribute.cs:40) — so it's excluded before it ever reaches GenerateAttributeInstantiation.
• The two TestMetadataGenerator.cs call sites (lines 1758/1777) only run for MethodDataSourceAttribute/InstanceMethodDataSourceAttribute fallbacks — never ArgumentsAttribute.
• StaticPropertyInitializationGenerator.cs:159-161 explicitly special-cases attributeClassName == "ArgumentsAttribute" and routes it to ParseArgumentsDataSourceWithAssignment before the GenerateAttributeInstantiation call at line 170 (which only fires for AsyncDataSourceGeneratorAttribute-derived types).
• InlineDataAttribute, the other type IsParamsArrayArgument checks for, doesn't exist anywhere in src/ as an actual attribute type.

So the entire IsParamsArrayArgument branch in GenerateAttributeInstantiation — not just the null case fixed here — looks unreachable today, for the same reason the decimal branch removed in commit 1 was unreachable: no caller currently feeds it an ArgumentsAttribute/InlineDataAttribute. The regression test added for this (CrossCompilationAttributeTests.cs:162-163, asserting ArgumentsAttribute(null)) is real and passes, but it exercises TestMetadataGenerator.WriteArgumentsAttributeFromTypedConstants (line 1567), which independently already had the identical IsNull check — not this function.

This is low severity since the fix is harmless either way, but given this PR's own stated goal (delete dead branches a previous review proved unreachable), it'd be more consistent to either:

1. Remove the whole IsParamsArrayArgument-guarded branch too (collapsing to the plain else path, same spirit as commit 1), or
2. If it's meant as defensive code for a future caller that does pass ArgumentsAttribute/InlineDataAttribute here, say so in the comment/description, and back it with a test that calls GenerateAttributeInstantiation directly rather than relying on end-to-end generator output that (as far as I can tell) routes through a different function.

Not a blocker — just flagging so the "unreachable code" cleanup goal lands fully rather than leaving a sibling dead branch behind.

[thomhurst]

Thanks. I checked the reachability claims and they hold:

• GenerateTestAttributes filters out IDataSourceAttribute implementations, and ArgumentsAttribute is one.
• Both TestMetadataGenerator call sites are inside GenerateMethodDataSourceAttribute, so they only see MethodDataSource/InstanceMethodDataSource.
• StaticPropertyInitializationGenerator sends ArgumentsAttribute to ParseArgumentsDataSourceWithAssignment before the GenerateAttributeInstantiation branch. That branch only takes async data-source generators.
• InlineDataAttribute doesn't exist in src/, and the exact-name check never matched ArgumentsAttribute<T> either.

So I went with option 1 in ef9cbb9. It removes the IsParamsArrayArgument branch and its helper. Constructor arguments are now always emitted straight from GetRawTypedConstantValue. This also replaces the null-array tweak from the previous commit.

About the test: the [Arguments(null)] assertion in CrossCompilationAttributeTests wasn't added by this PR. It came in with #6855, and it covers TestMetadataGenerator.WriteArgumentsAttributeFromTypedConstants, not this function. It's still a valid check for that path, so I left it alone.

Source generator tests pass on net472, net8.0, net9.0 and net10.0 (620 passed, 0 failed, 4 skipped as before), with no snapshot diffs.

About CI: the Windows PackTUnitFilesModule failure was a side effect. RunPublicAPITestsModule failed on net472 with Failed to resolve assembly: 'netstandard', which cancelled the pipeline and killed the in-progress dotnet pack. #6857 on main fixes that, and I've merged the latest main into this branch.

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[github-actions]

Review: remove unreachable decimal source-text path from GenerateAttributeInstantiation

Verdict: LGTM. Approving this as a clean dead-code removal with a well-documented rationale, and the PR has already been through several rounds of review (github-actions bot, CodeRabbit, Greptile) plus a legitimate follow-up that the author addressed by removing the sibling IsParamsArrayArgument branch too (commit ef9cbb9). I independently re-verified the key claims rather than just trusting the prior reviews:

What I checked

• Reachability of the removed branches: confirmed all 4 call sites of GenerateAttributeInstantiation (TestMetadataGenerator.cs lines 1758 and 1777, StaticPropertyInitializationGenerator.cs line 170, and the internal call in CodeGenerationHelpers.cs line 122) never pass targetParameters, so the removed parameterTypes/decimal-syntax branches were genuinely dead.
• ArgumentsAttribute/InlineDataAttribute unreachability (the concern raised in the review thread, addressed by the final commit): GenerateTestAttributes filters out anything implementing IDataSourceAttribute before it reaches this method, and ArgumentsAttribute implements that interface (src/TUnit.Core/Attributes/TestData/ArgumentsAttribute.cs:40). InlineDataAttribute does not exist anywhere in src/. The StaticPropertyInitializationGenerator call site explicitly routes ArgumentsAttribute to ParseArgumentsDataSourceWithAssignment before ever reaching the GenerateAttributeInstantiation branch (which is gated to AsyncDataSourceGeneratorAttribute-derived types only). So removing the whole IsParamsArrayArgument-guarded branch in the follow-up commit was correct, not just the null-array fix from the intermediate commit.
• No orphaned code: GetNullableUnderlyingType (used only by the removed branches in this file) is still used elsewhere (TypedConstantFormatter.cs), so nothing is left dangling.
• No public API impact: GenerateAttributeInstantiation is internal, and removing an optional parameter from an internal method needs no tests/TUnit.PublicAPI changes.
• Scope: correctly limited to TUnit.Core.SourceGenerator. Per AGENTS.md, metadata-collection changes need parity with TUnit.Engine, but this method has no engine-side counterpart, it is pure code-generation text-building, and execution afterward goes through the shared path, so no duplicate change is needed there.

Architectural note
No concerns to raise here, this is not a case that needs a different abstraction. The method is meaningfully simpler now (17 lines vs. roughly 190), the single remaining decision point (source-text vs. typed-constant for decimals) correctly lives in TestMetadataGenerator.TryGetDecimalLiteralText with its one call site, and keeping it private rather than extracting a shared helper is the right call since there is no second consumer. Good use of a prior review (linked PR #6855) to drive this cleanup rather than leaving dead branches to rot.

No blocking issues. Nice follow-through addressing the sibling dead-branch feedback instead of stopping at the original scope.