type-fest 0.13.1: Opaque

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify type-fest.Opaque in pkg:npm/type-fest@0.13.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/type-fest@0.13.1
Demonstrate these symbols/APIs:
  - type-fest.Opaque

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:f5de14faada3f460430ddb33f01fe2c4bd0bea32950e36f05921a644855f1992","contract":["type-fest package.json defines package name as type-fest and version as 0.13.1 with types entry point","type-fest index declarations export Opaque symbol","Opaque type definition exports generic type accepting Type and optional Token parameter defaulting to unknown","Opaque type definition intersects underlying Type with readonly __opaque__ property carrying Token","Opaque tag property __opaque__ is defined as readonly to prevent mutation"],"goal":"verify type-fest.Opaque in pkg:npm/type-fest@0.13.1","kind":"HOW","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"symbols":["type-fest.Opaque"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"subject":"pkg:npm/type-fest@0.13.1","symbols":["type-fest.Opaque"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-type-fest-opaque",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-type-fest-opaque",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "type-fest": "0.13.1"
      }
    },
    "node_modules/type-fest": {
      "version": "0.13.1",
      "resolved": "https://registry.npmjs.org/type-fest/-/type-fest-0.13.1.tgz",
      "integrity": "sha512-34R7HTnG0XIJcBSn5XhDd7nNFPRcXYRZrBB2O2jdKqYODldSzBAqzsWoZYYvduky73toYS/ESqxPvkDf/F0XMg==",
      "license": "(MIT OR CC0-1.0)",
      "engines": {
        "node": ">=10"
      },
      "funding": {
        "url": "https://github.com/sponsors/sindresorhus"
      }
    }
  }
}

{
  "name": "sample-type-fest-opaque",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "dependencies": {
    "type-fest": "0.13.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify type-fest.Opaque in pkg:npm/type-fest@0.13.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/type-fest@0.13.1"
  ],
  "symbols": [
    "type-fest.Opaque"
  ]
}

import assert from 'node:assert/strict';
import fs from 'node:fs';
import path from 'node:path';
import { createRequire } from 'node:module';

const require = createRequire(import.meta.url);

// Contract 1: type-fest package.json defines package name as type-fest and version as 0.13.1 with types entry point
{
  const pkgJson = require('type-fest/package.json');
  assert.equal(pkgJson.name, 'type-fest');
  assert.equal(pkgJson.version, '0.13.1');
  assert.equal(pkgJson.types, 'index.d.ts');
}

// Contract 2: type-fest index declarations export Opaque symbol
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const indexDtsPath = path.join(pkgDir, 'index.d.ts');
  assert.ok(fs.existsSync(indexDtsPath), 'index.d.ts must exist');
  const indexDtsContent = fs.readFileSync(indexDtsPath, 'utf8');
  assert.ok(
    indexDtsContent.includes("export {Opaque} from './source/opaque';"),
    'Opaque must be exported from index.d.ts'
  );
}

// Contract 3: Opaque type definition exports generic type accepting Type and optional Token parameter defaulting to unknown
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const opaqueDtsPath = path.join(pkgDir, 'source', 'opaque.d.ts');
  assert.ok(fs.existsSync(opaqueDtsPath), 'source/opaque.d.ts must exist');
  const opaqueDtsContent = fs.readFileSync(opaqueDtsPath, 'utf8');
  assert.ok(
    opaqueDtsContent.includes('export type Opaque<Type, Token = unknown> ='),
    'Opaque must be defined with generic Type and default Token = unknown'
  );
}

// Contract 4: Opaque type definition intersects underlying Type with readonly __opaque__ property carrying Token
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const opaqueDtsPath = path.join(pkgDir, 'source', 'opaque.d.ts');
  assert.ok(fs.existsSync(opaqueDtsPath), 'source/opaque.d.ts must exist');
  const opaqueDtsContent = fs.readFileSync(opaqueDtsPath, 'utf8');
  assert.ok(
    opaqueDtsContent.includes('Type & {readonly __opaque__: Token}'),
    'Opaque must intersect Type with {readonly __opaque__: Token}'
  );
}

// Contract 5: Opaque tag property __opaque__ is defined as readonly to prevent mutation
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const opaqueDtsPath = path.join(pkgDir, 'source', 'opaque.d.ts');
  assert.ok(fs.existsSync(opaqueDtsPath), 'source/opaque.d.ts must exist');
  const opaqueDtsContent = fs.readFileSync(opaqueDtsPath, 'utf8');
  assert.ok(
    opaqueDtsContent.includes('readonly __opaque__: Token'),
    '__opaque__ property must be marked readonly'
  );
}

console.log('All pkg:npm/type-fest@0.13.1 Opaque contracts passed successfully.');