# Notes for Mill Support Implementation - 2025-04-02

## Today's Accomplishments

1. Completed research on Mill build tool structure and extension development
2. Analyzed existing SBT infrastructure to understand equivalent implementation in Mill
3. Created proof-of-concept implementation of key components:
   - IWMillVersions - Centralized version management
   - IWMillDeps - Standardized dependency management
   - IWScalaModule - Standard module configuration
   - IWPublishModule - Publishing configuration

4. Created example project showing usage
5. Documented approach and usage in README.md

## Key Observations

### Advantages of Mill

1. More intuitive and readable build files
   - Regular Scala code vs. SBT's DSL
   - Method-based configuration vs. key-value pairs
   - Cleaner module definition and inheritance

2. Simpler extension development
   - Regular library vs. complex plugin system
   - Trait-based sharing of functionality
   - Easier to understand and maintain

3. Better performance
   - Aggressive caching of build tasks
   - More explicit task dependencies
   - Faster incremental compilation

4. Improved developer experience
   - Better IDE support with type-checked build files
   - More consistent error messages
   - Easier to debug and troubleshoot

### Implementation Notes

1. **IWMillVersions**
   - Direct port of IWMaterialsVersions
   - Same version constants, same naming scheme
   - Can be used directly by library users

2. **IWMillDeps**
   - Uses Mill's `ivy"org::name:version"` syntax
   - Same helper methods as IWMaterialsDeps (useZIO, useZIOAll, etc.)
   - Returns `Loose.Agg[Dep]` instead of SBT's `Seq[Def.Setting[_]]`

3. **IWScalaModule**
   - Extends Mill's ScalaModule and ScalafmtModule
   - Sets default Scala version (3.6.3)
   - Configures standard compiler options
   - Enables SemanticDB for tooling
   - Includes nested IWTests for standard test configuration

4. **IWPublishModule**
   - Configures publishing to IW Maven repositories
   - Handles snapshots vs. releases based on version
   - Uses environment variables for credentials

## Issues to Address

1. **Scala.js Support**
   - Need to implement IWScalaJSModule for JS compilation
   - Need to handle cross-platform dependencies properly
   - Need to support timezone and locale configuration

2. **Mill Plugin Ecosystem**
   - Need to identify and integrate with essential Mill plugins
   - Equivalent functionality to SBT plugins we currently use

3. **Testing Framework**
   - Currently using utest, but need to support ZIO Test
   - Need to configure proper test initialization

4. **Build Integration**
   - Need to test with Nix and direnv
   - Need to ensure compatibility with CI/CD pipelines

## Next Development Steps

### For Next Session (2025-04-03)

1. **Create IWScalaJSModule**
   - Support for Scala.js compilation
   - Cross-platform dependency handling
   - JS-specific configuration

2. **Enhanced Test Support**
   - Implement ZIO Test integration
   - Configure proper test initialization
   - Add test logging configurations

3. **Multi-Module Example**
   - Create example with multiple modules
   - Show inter-module dependencies
   - Demonstrate publishing configuration

### For Future Sessions

1. **Documentation**
   - Create comprehensive migration guide
   - Document all traits and components
   - Provide examples for different use cases

2. **Integration Testing**
   - Test with real-world projects
   - Measure performance vs. SBT
   - Validate build equivalence

3. **Release Planning**
   - Define versioning strategy
   - Setup CI/CD for the library
   - Create announcement for the team

## Migration Considerations

1. **Incremental Approach**
   - Start with new projects
   - Test on non-critical projects first
   - Gradually migrate existing projects

2. **Dual Build Configuration**
   - Initial phase: support both SBT and Mill
   - Update IWMaterialsVersions and IWMillVersions together
   - Maintain feature parity during transition

3. **Knowledge Transfer**
   - Create training materials
   - Run workshops for the team
   - Pair programming for initial migrations

4. **Compatibility Monitoring**
   - Keep track of SBT plugin updates
   - Ensure Mill implementation stays up to date
   - Regular testing of both build systems