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Add comprehensive GitHub Copilot instructions for AngleSharp.Diffing
Co-authored-by: egil <[email protected]>
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‎.github/copilot-instructions.md‎

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# AngleSharp.Diffing - HTML Comparison Library
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AngleSharp.Diffing is a .NET library for comparing AngleSharp control nodes and test nodes to identify differences between HTML DOM trees. This library targets .NET Standard 2.0 and provides a fluent API for HTML comparison and diffing.
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**Always reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.**
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## Working Effectively
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### Prerequisites and Setup
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- Install .NET 8.0+ SDK (already available in GitHub Actions environments)
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- Mono is NOT required for standard development (only for legacy Cake build system)
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### Bootstrap, Build, and Test
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Execute these commands in order from the repository root:
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```bash
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cd src
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dotnet restore # ~11 seconds - restores NuGet packages
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dotnet build # ~15 seconds - compiles library and tests
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dotnet test # ~5 seconds - runs 521 tests. NEVER CANCEL.
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```
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**CRITICAL TIMING EXPECTATIONS:**
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- `dotnet restore`: 11 seconds - NEVER CANCEL. Set timeout to 60+ seconds minimum.
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- `dotnet build`: 15 seconds - NEVER CANCEL. Set timeout to 60+ seconds minimum.
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- `dotnet test`: 5 seconds - runs 521 tests. NEVER CANCEL. Set timeout to 30+ seconds minimum.
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- Complete clean rebuild: ~20 seconds - NEVER CANCEL. Set timeout to 60+ seconds minimum.
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### Alternative Build Methods
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**PRIMARY METHOD (Recommended):** Use dotnet CLI commands as shown above.
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**LEGACY METHOD (Not Recommended):** The repository includes Cake build scripts (`build.sh`/`build.ps1`) but they require Mono and may fail. Only use if specifically needed:
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```bash
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# Install Mono first (if needed)
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sudo apt-get update && sudo apt-get install -y mono-complete
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./build.sh # May fail - use dotnet commands instead
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```
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### Release Builds and Packaging
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```bash
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cd src
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dotnet build --configuration Release # ~15 seconds
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dotnet pack --configuration Release # ~8 seconds - creates NuGet packages
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```
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**Package Output:** Creates `.nupkg` and `.snupkg` files in `src/AngleSharp.Diffing/bin/Release/`
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## Validation and Testing
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### Manual Validation Requirements
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**ALWAYS** validate changes by creating and running a test program to exercise the library:
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```csharp
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using AngleSharp.Diffing;
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// Test basic HTML diffing functionality
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var control = @"<p attr=""foo"">hello <em>world</em></p>";
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var test = @"<p attr=""bar"">hello <strong>world</strong></p>";
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var diffs = DiffBuilder
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.Compare(control)
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.WithTest(test)
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.Build()
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.ToList();
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Console.WriteLine($"Found {diffs.Count} differences:");
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foreach (var diff in diffs)
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{
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Console.WriteLine($"- {diff.GetType().Name}: {diff.Result} {diff.Target}");
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}
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```
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### Code Quality and Standards
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- **Code Analysis:** Project has strict analysis rules enabled (`EnforceCodeStyleInBuild=true`)
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- **EditorConfig:** Follow the existing `.editorconfig` settings (4-space indentation, CRLF line endings)
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- **Nullable References:** Enabled - handle null values appropriately
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- **Build Warnings:** Zero warnings expected - treat warnings as errors for critical types
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### Test Suite Information
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- **Test Framework:** xUnit with Shouldly assertions
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- **Test Count:** 521 tests covering core diffing functionality
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- **Test Runtime:** ~5 seconds total
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- **Test Files Location:** `src/AngleSharp.Diffing.Tests/`
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## Navigation and Architecture
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### Key Directories and Files
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```
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src/
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├── AngleSharp.Diffing/ # Main library project
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│ ├── Core/ # Core diffing engine and interfaces
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│ ├── Extensions/ # Extension methods
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│ ├── Strategies/ # Diffing strategy implementations
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│ └── DiffBuilder.cs # Main fluent API entry point
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├── AngleSharp.Diffing.Tests/ # Test project
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│ ├── Core/ # Core functionality tests
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│ └── Strategies/ # Strategy-specific tests
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└── AngleSharp.Diffing.sln # Solution file
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```
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### Important Classes and APIs
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- **`DiffBuilder`**: Main entry point with fluent API (`DiffBuilder.Compare(control).WithTest(test).Build()`)
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- **`IDiff`**: Base interface for all difference types
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- **`HtmlDifferenceEngine`**: Core comparison engine
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- **Diff Types**: `AttrDiff`, `NodeDiff`, `MissingNodeDiff`, `UnexpectedNodeDiff`, etc.
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### Dependencies
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- **AngleSharp 1.1.2**: Core HTML parsing library
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- **AngleSharp.Css 1.0.0-beta.144**: CSS support
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- **Target Framework**: .NET Standard 2.0 (library), .NET 8.0 (tests)
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## Common Development Tasks
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### Making Code Changes
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1. **Always build and test first** to establish baseline: `dotnet build && dotnet test`
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2. Make your changes to source files in `src/AngleSharp.Diffing/`
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3. **Immediately test after changes**: `dotnet build && dotnet test`
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4. **Manual validation**: Create a test program to exercise your changes
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5. **Pre-commit validation**: Ensure no build warnings or test failures
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### Debugging and Investigation
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- **Test filtering**: `dotnet test --filter "TestMethodName"` to run specific tests
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- **Verbose builds**: `dotnet build --verbosity normal` to see detailed output
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- **Key test files**: `DiffBuilderTest.cs` shows basic API usage patterns
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### CI/Build Requirements
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- **GitHub Actions**: Runs on both Linux and Windows
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- **Zero warnings policy**: Build must complete without warnings
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- **All tests must pass**: 521/521 tests required
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- **Code formatting**: Enforced via EditorConfig and analyzers
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## Getting Started Examples
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### Basic HTML Comparison
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```csharp
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var control = "<p>Expected content</p>";
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var test = "<p>Actual content</p>";
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var diffs = DiffBuilder
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.Compare(control)
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.WithTest(test)
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.Build();
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```
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### Advanced Configuration
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```csharp
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var diffs = DiffBuilder
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.Compare(control)
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.WithTest(test)
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.WithOptions(options => {
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// Configure diffing strategies
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})
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.Build();
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```
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### Working with Results
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```csharp
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foreach (var diff in diffs)
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{
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switch (diff.Result)
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{
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case DiffResult.Different:
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case DiffResult.Missing:
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case DiffResult.Unexpected:
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// Handle different types of differences
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break;
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}
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}
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```
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## Troubleshooting
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### Common Issues
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- **Build failures**: Ensure you're in the `src/` directory
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- **Cake build failures**: Use `dotnet` commands instead of `build.sh`/`build.ps1`
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- **Test failures**: Check for environment-specific issues or recent changes
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- **Package restore issues**: Clear NuGet caches with `dotnet nuget locals all --clear`
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### Quick Reset Commands
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```bash
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# Clean and rebuild everything
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cd src
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dotnet clean
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rm -rf */bin */obj
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dotnet restore
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dotnet build
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dotnet test
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```
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## Performance Expectations
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- **Development builds**: ~15 seconds
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- **Test execution**: ~5 seconds for full suite
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- **Package creation**: ~8 seconds
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- **CI builds**: Allow 60+ seconds timeout minimum for each step
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**CRITICAL**: NEVER CANCEL builds or tests that appear slow. Wait at least 60 seconds for builds and 30 seconds for tests before considering alternatives.

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