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CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+OpenSwiftUI is an open source implementation of Apple's SwiftUI framework, designed to:
+- Build GUI apps on non-Apple platforms (Linux, Windows)  
+- Diagnose and debug SwiftUI issues on Apple platforms
+- Maintain API compatibility with SwiftUI
+
+This project is in active development and contains multiple Swift packages with extensive environment-based configuration.
+
+## Build Commands
+
+### Standard Build
+```bash
+./Scripts/build.sh
+# Or directly: swift build
+```
+
+### Build with Library Evolution
+```bash
+./Scripts/build_swiftinterface.sh
+# Generates module interfaces for library evolution
+```
+
+### Environment Variables
+The build system uses many environment variables for configuration:
+- `OPENSWIFTUI_BUILD_FOR_DARWIN_PLATFORM`: Build for Darwin platforms (default: true on macOS)
+- `OPENSWIFTUI_DEVELOPMENT`: Enable development mode features
+- `OPENSWIFTUI_USE_LOCAL_DEPS`: Use local dependency paths instead of remote repos
+- `OPENSWIFTUI_LIBRARY_EVOLUTION`: Enable library evolution support
+- `OPENSWIFTUI_COMPATIBILITY_TEST`: Run compatibility tests with SwiftUI
+
+## Test Commands
+
+### Run All Tests
+```bash
+swift test
+```
+
+### Run Specific Test Target
+```bash
+swift test --filter OpenSwiftUICoreTests
+swift test --filter OpenSwiftUICompatibilityTests
+swift test --filter OpenSwiftUISymbolDualTests
+```
+
+### Test with Coverage
+```bash
+swift test --enable-code-coverage
+```
+
+### List Available Tests
+```bash
+swift test --list-tests
+```
+
+## Dependencies Setup
+
+The project requires cloning additional repositories in the same parent directory:
+
+```bash
+cd ..
+git clone https://github.com/OpenSwiftUIProject/OpenAttributeGraph.git
+git clone https://github.com/OpenSwiftUIProject/OpenRenderBox.git
+git clone https://github.com/OpenSwiftUIProject/DarwinPrivateFrameworks.git
+```
+
+## Architecture
+
+### Core Modules
+
+1. **OpenSwiftUI_SPI**: System Programming Interface and low-level utilities
+2. **OpenSwiftUICore**: Core framework implementation with animations, layout, graphics
+3. **OpenSwiftUI**: Main public API layer, SwiftUI-compatible interface
+4. **OpenSwiftUIExtension**: Additional APIs extending OpenSwiftUI/SwiftUI
+5. **OpenSwiftUIBridge**: Bridge layer for migrating from other frameworks
+
+### Key Source Directories
+
+- `Sources/OpenSwiftUICore/`: Core implementation (Animation, Layout, Graphics, etc.)
+- `Sources/OpenSwiftUI/`: Public API layer matching SwiftUI
+- `Sources/OpenSwiftUI_SPI/`: Low-level system interfaces and utilities
+- `Sources/COpenSwiftUI/`: C/Objective-C interop code
+- `Tests/`: Comprehensive test suites for all modules
+- `Example/`: Demo applications and UI tests
+
+### Testing Framework
+
+The project uses **swift-testing framework** (not XCTest):
+- Import with `import Testing`
+- Use `@Test` attribute for test functions
+- Use `#expect()` for assertions instead of XCTest assertions
+- No comments in test case bodies - keep tests clean and self-explanatory
+
+### Code Style (from .github/copilot-instructions.md)
+
+- Use `package` access level for cross-module APIs
+- 4-space indentation, trim trailing whitespaces
+- Use `// MARK: -` to separate code sections
+- Maximum line length: 120 characters (soft limit)
+- Follow SwiftUI API compatibility patterns
+- Prefix internal types with `_` when mirroring SwiftUI internals
+
+### Platform Support
+
+- **Darwin Platforms**: Currently only iOS and macOS are supported
+- **Linux**: Build and test support, some features limited
+- **Windows**: Not yet supported
+
+### Development Configurations
+
+For the Example app:
+- `SwiftUIDebug`: Run with Apple's SwiftUI
+- `OpenSwiftUIDebug`: Run with OpenSwiftUI implementation
+
+## Environment Configuration
+
+The Package.swift heavily uses environment variables for conditional compilation:
+- Most features are platform-dependent (Darwin vs non-Darwin)
+- Development mode enables additional debugging features
+- Library evolution mode generates .swiftinterface files
+- Various private framework integrations can be toggled
+
+## Important Notes
+
+- This project uses private Apple APIs and frameworks - NOT for App Store distribution
+- SwiftUI compatibility is the primary goal - match Apple's API signatures exactly  
+- The project requires Swift 6.1.2+ and specific platform versions
+- Cross-platform support relies on custom implementations of Apple frameworks