scala-cli-adding-directives
Add or change using directives in Scala CLI. Use when adding a new //> using directive, registering a directive handler, or editing directive preprocessing.
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- VirtusLab/scala-cli
- Last source activity
- March 18, 2026 at 07:40
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- English
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- scala-cli-adding-directives
- description
- Add or change using directives in Scala CLI. Use when adding a new //> using directive, registering a directive handler, or editing directive preprocessing.
# Adding a new directive (Scala CLI)
1. **Create a case class** in `modules/directives/src/main/scala/scala/build/preprocessing/directives/` extending one of:
- `HasBuildOptions` — produces `BuildOptions` directly
- `HasBuildOptionsWithRequirements` — produces `BuildOptions` with scoped requirements (e.g. `test.dep`)
- `HasBuildRequirements` — produces `BuildRequirements` (for `//> require`)
2. **Annotate**: `@DirectiveLevel(SpecificationLevel.EXPERIMENTAL)`, `@DirectiveDescription("…")`, `@DirectiveUsage("…")`, `@DirectiveExamples("…")`, `@DirectiveName("key")` on fields.
3. **Companion**: `val handler: DirectiveHandler[YourDirective] = DirectiveHandler.derive`
4. **Register** in `modules/build/.../DirectivesPreprocessingUtils.scala` in the right list: `usingDirectiveHandlers`, `usingDirectiveWithReqsHandlers`, or `requireDirectiveHandlers`.
5. **Regenerate reference docs**: `./mill -i 'generate-reference-doc[]'.run`
CLI options always override directive values when both set the same thing.
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