# Tooling ## _Build-Time Safety for Higher-Kinded-J_ > _"Make illegal states unrepresentable."_ > — Yaron Minsky Every Path type in Higher-Kinded-J can only chain with the same type. Mix a `MaybePath` into an `EitherPath` chain, and you get an `IllegalArgumentException` at runtime. The code compiles; the tests pass (until someone hits that branch); production breaks at 2 AM. The HKJ tooling catches these mistakes before your code ever runs. Both Gradle and Maven are supported with dedicated build plugins. --- ~~~admonish info title="In This Chapter" - **[Build Plugins](gradle_plugin.md)**: One-line setup for Gradle or Maven that configures dependencies, preview features, and compile-time checks automatically. This is the recommended way to add Higher-Kinded-J to a project; reach for it first. - **[Manual Gradle and Maven Setup](manual_setup.md)**: Full `build.gradle.kts` and `pom.xml` configuration for the projects that cannot use the build plugin (constrained environments, in-house build frameworks, or a conflicting plugin). The fallback, not the starting point. - **[Compile-Time Checks](compile_checks.md)**: A javac plugin that detects Path type mismatches at compile time, preventing runtime `IllegalArgumentException` errors. Follows a strict no-false-positives policy. - **[Migration Recipes](openrewrite.md)**: The `hkj-openrewrite` recipe catalogue for upgrading between Higher-Kinded-J releases. Covers the 0.2.x to 0.3.0 arity migration, detection-only effect-algebra helpers, and the 0.5.0 deprecation migration; runnable from Gradle or Maven. - **[Diagnostics](diagnostics.md)**: The `hkjDiagnostics` Gradle task or `mvn hkj:diagnostics` Maven goal that reports your current HKJ configuration, showing exactly which dependencies, compiler arguments, and checks are active. - **[Traversal Generator Plugins](generator_plugins.md)**: The 30 built-in generators that power `@GenerateTraversals`, covering JDK collections, HKJ core types, and five third-party libraries (Eclipse Collections, Guava, Vavr, Apache Commons, PCollections). Includes a guide to writing your own generator for custom container types. - **[PCollections Integration](pcollections_integration.md)**: Tests, benchmarks, and an example that confirm PCollections persistent collections (`PVector`, `PStack`) compose with the existing `ListKind` infrastructure through `java.util.List` compatibility, with no production code changes. - **[PCollections Optics](pcollections_optics.md)**: Seven `@GenerateTraversals` plugins that recognise `PVector`, `PStack`, `PSet`, `PSortedSet`, `PBag`, `PMap`, and `PSortedMap` fields and generate type-correct traversals against them. - **[Claude Code Skills](claude_code_skills.md)**: Eight bundled skills that bring contextual HKJ guidance directly into your editor. Covers Path selection, optics, record mapping, effect handlers, the effects-optics bridge, Spring Boot integration, functional core / imperative shell architecture, and AssertJ-based testing with hkj-test. - **[Testing With hkj-test](test_assertions.md)**: A test-scope dependency that ships fluent AssertJ helpers for every HKJ type. Replaces hand-written unwrapping with assertions that read like the business intent: `isRight()`, `hasJustValue(...)`, `whenExecuted().hasValue(...)`, and so on across discriminated unions, effect types, and monad transformers. ~~~ ## Chapter Contents 1. [Build Plugins](gradle_plugin.md) - One-line project setup for Gradle and Maven (recommended) 2. [Manual Gradle and Maven Setup](manual_setup.md) - Full manual build configuration (fallback) 3. [Compile-Time Checks](compile_checks.md) - Path type mismatch detection 4. [Migration Recipes](openrewrite.md) - OpenRewrite recipes for upgrading between releases 5. [Diagnostics](diagnostics.md) - Configuration reporting and troubleshooting 6. [Traversal Generator Plugins](generator_plugins.md) - Supported types and custom generators 7. [PCollections Integration](pcollections_integration.md) - PCollections compatibility through `ListKind` 8. [PCollections Optics](pcollections_optics.md) - `@GenerateTraversals` plugins for PCollections types 9. [Claude Code Skills](claude_code_skills.md) - In-editor guidance via Claude Code 10. [Testing With hkj-test](test_assertions.md) - Fluent assertions for HKJ types --- **Next:** [Build Plugins](gradle_plugin.md)