Background file health checks

warlock dev checks saved source files after boot and as they change. TypeScript and configured, app-installed Oxlint run in dedicated workers by default. HTTP /health and /ready probes are configured separately. ESLint support was removed in 5.34.0; see toolchain migration.

Enable Oxlint

Install Oxlint in your app:

npm install --save-dev oxlint
# or
yarn add --dev oxlint

Add .oxlintrc.json at the app root:

{
  "rules": {
    "no-debugger": "error",
    "no-unused-vars": "warn"
  }
}

Start warlock dev. The checker resolves the app’s Oxlint CLI package and invokes it with the changed file list in a worker. JSON diagnostics become file errors and warnings, including their rule id, line, column and span. It reads saved files from disk, honors Oxlint config and ignore rules, and skips deleted and unsupported files. Empty change batches never trigger a whole-project scan. Large boot scans are split into sequential batches within platform command-line limits (counting each argument’s argv pointer on POSIX systems) and at most 500 files each; file paths are passed relative to the app root. A batch whose JSON report overflows the 8 MiB output buffer is split in half and retried, down to single files. A path too long for the conservative budget runs in a batch of its own, and if the operating system still refuses it (E2BIG/ENAMETOOLONG) only that file is reported as an unchecked warning; the rest of the scan continues. Tool/config errors include the CLI’s output and are printed without stopping the dev server. During shutdown the worker sends SIGTERM to a running CLI child and SIGKILL 250 ms later if it is still running; a check cut short this way reports “Oxlint check cancelled: the development server is shutting down.” and is not printed as a failure.

Oxlint also discovers .oxlintrc.jsonc, oxlint.config.ts and oxlint.config.mts. Use JSON or JSONC at Warlock’s Node.js 22.15 minimum; current Oxlint TypeScript configuration requires Node.js 22.18 or newer. See the Oxlint configuration guide.

Select built-in checkers

import { defineConfig } from "@warlock.js/core";

export default defineConfig({
  devServer: {
    healthCheckers: {
      typescript: true,
      oxlint: true,
    },
  },
});

Omitted switches keep TypeScript on and Oxlint on when its app-root config and package exist. Set either switch to false to disable that checker. Restart the dev server after installing Oxlint or adding its initial config.

Existing custom checker arrays keep replacing the complete built-in list. devServer.healthCheckers: false disables all checks, and warlock dev --skip-health overrides any checker configuration for that run. These switches are independent of devServer.generateTypings.

Oxlint config failures preserve both warning and error output; structured diagnostics keep their specific message. Command failure messages contain a bounded status/output summary, without the batch command line. Shutdown gives workers up to 500 ms to exit and reap owned CLI children before forcing termination.

Source TypeScript health workers use the framework’s JavaScript bootstrap to register tsx inside each worker on Node.js 22.15 and Node.js 24. Registration remains active for later TypeScript imports and lets native dependencies load Node builtins through createRequire. Published JavaScript workers start directly. Their TypeScript and native parser dependencies remain external and resolve from core’s installed dependencies; native optional bindings load from the parser package’s own location. Regression tests cover both paths without inherited loader hooks, including configured declaration roots, source updates and deleted declarations.