type-fest 0.13.1: MergeExclusive

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.MergeExclusive 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.MergeExclusive

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:e7d09d646601eb376c450ac1df62dfb418a302626ae9f6c4d2db275ad4c29abd","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 MergeExclusive symbol","Without helper type produces mapped type with keys from FirstType excluded from SecondType set to optional never","MergeExclusive type definition conditionally checks if union of FirstType and SecondType extends object","MergeExclusive type definition constructs union of mutually exclusive intersections with Without helper"],"goal":"verify type-fest.MergeExclusive in pkg:npm/type-fest@0.13.1","kind":"HOW","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"symbols":["type-fest.MergeExclusive"]},"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.MergeExclusive"],"verifierAdapter":"node-typescript@1"}

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

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

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 MergeExclusive 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 {MergeExclusive} from './source/merge-exclusive';"),
    'MergeExclusive must be exported from index.d.ts'
  );
}

// Contract 3: Without helper type produces mapped type with keys from FirstType excluded from SecondType set to optional never
{
  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 dtsContent = fs.readFileSync(mergeExclusiveDtsPath, 'utf8');
  assert.ok(
    dtsContent.includes('type Without<FirstType, SecondType> ='),
    'Without helper type must be defined'
  );
  assert.ok(
    dtsContent.includes('[KeyType in Exclude<keyof FirstType, keyof SecondType>]?: never'),
    'Without helper type must map excluded keys to optional never'
  );
}

// Contract 4: MergeExclusive type definition conditionally checks if union of FirstType and SecondType extends object
{
  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 dtsContent = fs.readFileSync(mergeExclusiveDtsPath, 'utf8');
  assert.ok(
    dtsContent.includes('export type MergeExclusive<FirstType, SecondType> ='),
    'MergeExclusive type must be exported'
  );
  assert.ok(
    dtsContent.includes('(FirstType | SecondType) extends object ?'),
    'MergeExclusive must check if (FirstType | SecondType) extends object'
  );
}

// Contract 5: MergeExclusive type definition constructs union of mutually exclusive intersections with 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 dtsContent = fs.readFileSync(mergeExclusiveDtsPath, 'utf8');
  assert.ok(
    dtsContent.includes('(Without<FirstType, SecondType> & SecondType) | (Without<SecondType, FirstType> & FirstType)'),
    'MergeExclusive must construct union of Without and opposing type intersections'
  );
  assert.ok(
    dtsContent.includes('FirstType | SecondType;'),
    'MergeExclusive must fallback to FirstType | SecondType for non-objects'
  );
}

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