Copilot instructions

Build, test, and lint

Use Node.js 24 or later (package.json declares >=24.0.0).

• npm ci installs the locked dependencies.
• npm test runs Jest serially with coverage.
• npm test -- --runTestsByPath __tests__/setup-java.test.ts runs one test file.
• npm test -- --runTestsByPath __tests__/setup-java.test.ts --testNamePattern="pattern" filters that file to matching test names.
• npm run lint runs ESLint on TypeScript files.
• npm run format-check checks Prettier formatting; npm run format applies it.
• npm run build bundles the setup and post-job entrypoints into dist/.
• npm run check runs format check, lint, build, and the full test suite.

Architecture

This repository implements a Node.js GitHub Action. action.yml defines its inputs and outputs and runs dist/setup/index.js as the main entrypoint and dist/cleanup/index.js as the post-job entrypoint. The TypeScript sources in src/ are bundled with NCC; the committed dist/ files are what the action executes.

The setup entrypoint parses inputs, resolves versions, and configures the action's shared features. src/distributions/distribution-factory.ts lazily selects a vendor installer. Vendor installers implement metadata lookup and archive handling on top of JavaBase in src/distributions/base-installer.ts, which centralizes version resolution, tool-cache/JDK-cache use, download verification, and Java environment setup. Package support and OS/architecture support are validated centrally in package-types.ts and platform-types.ts.

The setup flow also configures problem matchers, Maven authentication and arguments, and Maven toolchains. The post-job entrypoint removes any isolated GPG home and saves enabled caches when the job succeeds and cache saving is not read-only.

Repository-specific conventions

• Keep TypeScript source imports ESM-compatible: relative imports include the .js extension, even when the source file is .ts.
• Distribution-specific download and metadata logic belongs in its installer under src/distributions/; reuse JavaBase rather than duplicating common resolution, caching, verification, or environment behavior.
• When adding or changing distribution support, keep the distribution enum, factory, package-capability map, platform-capability map, README support documentation, unit tests, and relevant end-to-end workflow coverage consistent.
• Unit tests live under __tests__/ and use Jest/ts-jest. Distribution tests are grouped under __tests__/distributors/; use the corresponding test and fixture patterns when changing an installer. End-to-end coverage is defined in .github/workflows/e2e-*.yml.
• Rebuild and commit generated dist/ bundles for runtime-affecting source or dependency changes; do not make the bundles the source of truth. npm run check includes the build.
• New npm dependencies need lockfile changes and corresponding license records under .licenses/, following .licensed.yml and the licensed workflow.

Action behavior principles

• Treat action.yml inputs, outputs, defaults, and compatibility aliases as the public API. Keep implementation, README, and advanced-usage documentation aligned when behavior changes; preserve deprecated aliases unless a documented breaking change removes them.
• Do not assume version syntax, package variants, or platform/architecture support is uniform across distributions. Keep capability checks and vendor resolution behavior consistent with the documented support matrix. latest means the newest stable GA release, not an early-access build.
• Preserve selection semantics: a recognized vendor in a supported version file may supply the distribution; otherwise the caller must provide it. If both java-version and java-version-file are given, the explicit java-version takes precedence.
• Preserve install-state behavior for multiple JDKs. The last installed JDK becomes the default unless set-default: false; all installed JDKs remain available through their version-specific environment variables and Maven toolchains. Toolchain entries accumulate non-destructively, and custom IDs must correspond one-for-one with requested versions.
• Treat dependency, wrapper, and JDK caches as distinct features with distinct keys and save behavior. cache enables dependency caching and implicitly enables JDK caching unless cache-jdk overrides it; cache-read-only restores without saving. Keep changes to cache identity or lifecycle aligned with these documented contracts.
• Preserve download-integrity guarantees: verify authoritative checksums when published. Signature verification is distribution-specific; explicit verify-signature: true must enforce verification where supported and fail clearly where unsupported. Do not silently weaken verification or imply that a cached install was downloaded and reverified.
• Keep Maven credential inputs as environment-variable names, not secret values. Generated settings and custom repository behavior must respect the documented overwrite option, while toolchain merging remains non-destructive and independent of that option.

See docs/CONTRIBUTING.md for contribution and validation guidance, README.md for the public contract, and docs/advanced-usage.md for detailed behavior and examples.