[duplicate-code] Duplicate Code: Polyfill File Structure Boilerplate

[Evangelink]

🔍 Duplicate Code Detected: Polyfill File Structure Boilerplate

Analysis of commit ed7ecb2

Summary

The newly added polyfill files in src/Polyfills/ contain repetitive structural boilerplate with identical file headers, conditional compilation directives, using statements, and #else clauses. This pattern is duplicated across 23 files with over 400 lines of repeated boilerplate code.

Duplication Details

Pattern: Polyfill File Structure

• Severity: High

• Occurrences: 23 files

• Total Duplicate Lines: ~400+ lines

• Locations:

  • src/Polyfills/CallerArgumentExpressionAttribute.cs (lines 1-7, 33-35)
  • src/Polyfills/CompilerFeatureRequiredAttribute.cs (lines 1-7, 48-50)
  • src/Polyfills/ExperimentalAttribute.cs (lines 1-7, 53-55)
  • src/Polyfills/IsExternalInit.cs (lines 1-7, 18-20)
  • src/Polyfills/ModuleInitializerAttribute.cs (lines 1-10, 22-24)
  • src/Polyfills/RequiredMemberAttribute.cs (lines 1-12, 25-27)
  • src/Polyfills/InterpolatedStringHandlerAttribute.cs (lines 1-6, 18-20)
  • src/Polyfills/InterpolatedStringHandlerArgumentAttribute.cs (lines 1-6, 30-32)
  • src/Polyfills/StackTraceHiddenAttribute.cs (lines 1-6, 14-16)
  • src/Polyfills/UnconditionalSuppressMessageAttribute.cs (lines 1-8, 92-94)
  • src/Polyfills/DynamicallyAccessedMembersAttribute.cs (lines 1-9, 60-62)
  • src/Polyfills/PlatformAttributes.cs (lines 1-8, 194-202)
  • Plus 11 more files with similar patterns

• Code Sample:

// Repeated in 23 files:
// <auto-generated />

#pragma warning disable

#if !NETCOREAPP

using Microsoft.CodeAnalysis;

namespace System.Runtime.CompilerServices; // or other namespaces

// ... actual polyfill implementation ...

#else
[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(...))]
#endif

Impact Analysis

• Maintainability: Any change to the file structure pattern (e.g., updating the conditional compilation directive, changing the auto-generated marker, or adjusting the pragma directives) requires modifying 23 separate files.
• Bug Risk: Inconsistent application of the pattern across files can lead to build errors or unexpected behavior in different target frameworks.
• Code Bloat: Approximately 400+ lines of repeated boilerplate code that could be eliminated or reduced through abstraction.
• Consistency: Currently, there are minor variations in the pattern (e.g., some files include #nullable enable, some have different using statement orders), indicating the pattern is not centrally managed.

Refactoring Recommendations

1. T4 Template or Source Generator Approach (Recommended)

• Create a T4 template or Roslyn source generator that generates the polyfill files with consistent structure
• Define polyfill metadata in a central configuration file (e.g., JSON or XML)
• Generate all polyfill files during build from the template
• Estimated effort: 8-12 hours
• Benefits:
  • Single source of truth for file structure
  • Guaranteed consistency across all polyfills
  • Easy to update all files by changing the template
  • Reduces manual errors

2. Shared .props File for Common Directives

• Extract common MSBuild properties and conditional compilation symbols to a shared .props file
• Use MSBuild targets to inject common file headers
• Estimated effort: 4-6 hours
• Benefits:
  • Centralizes compilation settings
  • Reduces some boilerplate
• Limitations:
  • Cannot eliminate in-file boilerplate completely

3. Base Class/Helper for Common Patterns

• For polyfills that share common structure, consider using a base class or helper methods
• Estimated effort: 6-8 hours
• Benefits:
  • Reduces code duplication
• Limitations:
  • May not be applicable to all polyfill types (attributes, static classes, etc.)
  • Could complicate type-forwarding logic

Implementation Checklist

• Review duplication findings with team
• Decide on refactoring approach (T4 template vs. source generator vs. hybrid)
• Create template or generator infrastructure
• Migrate existing polyfill files to use the new approach
• Update build scripts to generate polyfills during build
• Verify all target frameworks build correctly
• Update documentation for adding new polyfills
• Consider adding automated checks to prevent manual polyfill additions

Analysis Metadata

• Analyzed Files: 48 C# source files
• Detection Method: Semantic code analysis with pattern matching
• Commit: ed7ecb2
• Analysis Date: 2026-05-26T05:35:57Z
• Repository: microsoft/testfx

Generated by Duplicate Code Detector · ● 1.5M · ◷

Add this agentic workflows to your repo

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/duplicate-code-detector.md@main

• expires on May 28, 2026, 5:43 AM UTC