type-fest 0.13.1: Merge, MergeExclusive, RequireAtLeastOne

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 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:
  - Merge
  - MergeExclusive
  - RequireAtLeastOne

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:a5b6e97484d59dc6aaed8b39cd537916439d1ac448b131a8a46a14a2348f2ef0","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 Merge, MergeExclusive, and RequireAtLeastOne symbols","Merge type definition combines two types overriding keys of the first type with the second type using Except and Extract","MergeExclusive type definition creates mutually exclusive key union type using Without helper","RequireAtLeastOne type definition creates type requiring at least one key while keeping remaining keys optional"],"goal":"verify pkg:npm/type-fest@0.13.1","kind":"HOW","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"symbols":["Merge","MergeExclusive","RequireAtLeastOne"]},"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":["Merge","MergeExclusive","RequireAtLeastOne"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-type-fest-merge-utility",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-type-fest-merge-utility",
      "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-merge-utility",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "dependencies": {
    "type-fest": "0.13.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/type-fest@0.13.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/type-fest@0.13.1"
  ],
  "symbols": [
    "Merge",
    "MergeExclusive",
    "RequireAtLeastOne"
  ]
}

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 Merge, MergeExclusive, and RequireAtLeastOne symbols
{
  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 {Merge} from './source/merge';"), 'Merge must be exported from index.d.ts');
  assert.ok(indexDtsContent.includes("export {MergeExclusive} from './source/merge-exclusive';"), 'MergeExclusive must be exported from index.d.ts');
  assert.ok(indexDtsContent.includes("export {RequireAtLeastOne} from './source/require-at-least-one';"), 'RequireAtLeastOne must be exported from index.d.ts');
}

// Contract 3: Merge type definition combines two types overriding keys of the first type with the second type using Except and Extract
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const mergeDtsPath = path.join(pkgDir, 'source', 'merge.d.ts');
  assert.ok(fs.existsSync(mergeDtsPath), 'source/merge.d.ts must exist');
  const mergeDtsContent = fs.readFileSync(mergeDtsPath, 'utf8');
  assert.ok(
    mergeDtsContent.includes('export type Merge<FirstType, SecondType> = Except<FirstType, Extract<keyof FirstType, keyof SecondType>> & SecondType;'),
    'Merge must be defined using Except, Extract and intersection'
  );
}

// Contract 4: MergeExclusive type definition creates mutually exclusive key union type using Without helper
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const mergeExclusiveDtsPath = path.join(pkgDir, 'source', 'merge-exclusive.d.ts');
  assert.ok(fs.existsSync(mergeExclusiveDtsPath), 'source/merge-exclusive.d.ts must exist');
  const mergeExclusiveDtsContent = fs.readFileSync(mergeExclusiveDtsPath, 'utf8');
  assert.ok(
    mergeExclusiveDtsContent.includes('type Without<FirstType, SecondType> = {[KeyType in Exclude<keyof FirstType, keyof SecondType>]?: never};'),
    'Without helper type must be defined'
  );
  assert.ok(
    mergeExclusiveDtsContent.includes('export type MergeExclusive<FirstType, SecondType> ='),
    'MergeExclusive type must be exported'
  );
}

// Contract 5: RequireAtLeastOne type definition creates type requiring at least one key while keeping remaining keys optional
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const requireAtLeastOneDtsPath = path.join(pkgDir, 'source', 'require-at-least-one.d.ts');
  assert.ok(fs.existsSync(requireAtLeastOneDtsPath), 'source/require-at-least-one.d.ts must exist');
  const requireAtLeastOneDtsContent = fs.readFileSync(requireAtLeastOneDtsPath, 'utf8');
  assert.ok(
    requireAtLeastOneDtsContent.includes('export type RequireAtLeastOne<ObjectType, KeysType extends keyof ObjectType = keyof ObjectType>'),
    'RequireAtLeastOne must constrain KeysType'
  );
  assert.ok(
    requireAtLeastOneDtsContent.includes('& Except<ObjectType, KeysType>'),
    'RequireAtLeastOne must preserve remaining keys with Except'
  );
}

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