ADR-15: C# Preprocessor Block Attribute Detection Limitation

🇰🇷 Korean Version

Date	Author	Repository
2026-01-04	@KubrickCode	core

Status: Accepted

Background

Problem Definition

The tree-sitter-c-sharp grammar parses preprocessor directives (#if, #else, #elif) between attributes as ERROR nodes instead of preproc_if nodes.

Discovery

Validation of fluentassertions/fluentassertions repository:

• Ground Truth (AI Manual Analysis): 5,995 tests
• Parser Result: 6,009 tests
• Delta: +14 (+0.23%)

The delta is positive because GT analysis errors outnumber parser bugs. The actual parser bug caused 2 tests to be missed in AssertionExtensionsSpecs.cs.

Technical Analysis

// InlineData(2) is not detected in this pattern
[Theory]
[InlineData(1)]
#if NET6_0_OR_GREATER
[InlineData(2)]  // ← Parser misses this
#endif
public void Test(int x) { }

Actual tree-sitter parsing result:

method_declaration
├── attribute_list [Theory]
├── attribute_list [InlineData(1)]
├── ERROR                          ← Not preproc_if!
│   └── #if NET6_0_OR_GREATER
│       └── (InlineData(2) incorrectly parsed)
└── public void Test()

Note: Class-level #if (wrapping entire methods) works correctly:

// This pattern is detected correctly
#if NET6_0_OR_GREATER
[Fact]
public void Net6OnlyTest() { }
#endif

Decision

Test attribute detection inside preprocessor blocks between attributes is not supported.

This is a tree-sitter-c-sharp grammar-level issue that cannot be fixed in the SpecVital Core parser.

Rationale

1. Grammar-level limitation: tree-sitter-c-sharp generates incorrect AST, making parser-level workaround impossible
2. Upstream dependency: Fix requires modifying the tree-sitter-c-sharp grammar itself
3. Limited impact: Most C# projects don't use preprocessors between attributes

Options Considered

Option A: Accept Limitation and Document (Selected)

Document the limitation and verify behavior with tests.

Pros:

• Honest representation of limitations
• Automatically resolved if tree-sitter-c-sharp is fixed

Cons:

• Test under-count in certain codebases

Option B: Text-based Preprocessor Expansion

Process preprocessor directives at text level before AST parsing.

Pros:

• Can detect attributes inside preprocessor blocks

Cons:

• Complexity explosion: Requires condition evaluation, nesting handling, multiple branch processing
• Accuracy degradation: Cannot know which conditions are active
• Architecture violation: Conflicts with tree-sitter-based parsing principles

Option C: Fork tree-sitter-c-sharp

Directly modify the grammar to support preprocessors between attributes.

Pros:

• Fundamental solution

Cons:

• Maintenance burden: Must continuously merge upstream changes
• Scope creep: Forking entire grammar for single issue
• Uncertainty: Difficult to predict side effects of grammar modification

Consequences

Positive

1. Architecture integrity: Maintains tree-sitter-based parsing model
2. Clear limitations: Documented in code comments and tests
3. Maintainability: No complex workarounds

Negative

1. Accuracy gap: Projects using preprocessors between attributes will have under-counted tests
2. FluentAssertions impact: Under-count due to [InlineData] usage in #if blocks

Mitigation

1. Minimal impact: Most projects don't use this pattern
2. Class-level works: #if wrapping entire methods works correctly
3. Documentation: Limitation documented in GetAttributeLists() function comment

Framework Impact

Framework	Affected Pattern	Severity
xUnit	[InlineData] in #if	Low
NUnit	[TestCase] in #if	Low
MSTest	[DataRow] in #if	Low

Most C# test projects use class-level or method-level conditional compilation. The pattern of inserting preprocessors between attributes is rare.

Related ADRs

• ADR-02: Dynamic Test Counting Policy - Another accuracy limitation
• ADR-03: Tree-sitter AST Parsing Engine - Tree-sitter-based parsing principles
• ADR-14: Indirect Import Alias Detection Unsupported - Similar limitation documentation pattern

References

• tree-sitter-c-sharp GitHub
• Validation Report: realworld-test-report.md
• Limitation Test: pkg/parser/strategies/shared/dotnetast/ast_test.go:TestGetAttributeLists_PreprocessorLimitation