type-fest 0.13.1: UnionToIntersection

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.UnionToIntersection 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.UnionToIntersection

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:a372ed85d5eafd55713a852b4c85e35590b9751933c933a277288965019953da","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 UnionToIntersection symbol from source/union-to-intersection","UnionToIntersection source declaration file exists and exports UnionToIntersection type","UnionToIntersection converts union of types into intersection using distributive conditional types and function argument inference","UnionToIntersection documentation provides usage examples demonstrating union object types merged into single intersection"],"goal":"verify type-fest.UnionToIntersection in pkg:npm/type-fest@0.13.1","kind":"HOW","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"symbols":["type-fest.UnionToIntersection"]},"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.UnionToIntersection"],"verifierAdapter":"node-typescript@1"}

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

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

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 UnionToIntersection symbol from source/union-to-intersection
{
  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 {UnionToIntersection} from './source/union-to-intersection';"),
    'UnionToIntersection must be exported from index.d.ts'
  );
}

// Contract 3: UnionToIntersection source declaration file exists and exports UnionToIntersection type
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const u2iDtsPath = path.join(pkgDir, 'source', 'union-to-intersection.d.ts');
  assert.ok(fs.existsSync(u2iDtsPath), 'source/union-to-intersection.d.ts must exist');
  const content = fs.readFileSync(u2iDtsPath, 'utf8');
  assert.ok(
    content.includes('export type UnionToIntersection<Union> ='),
    'UnionToIntersection must export generic Union type parameter'
  );
}

// Contract 4: UnionToIntersection converts union of types into intersection using distributive conditional types and function argument inference
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const u2iDtsPath = path.join(pkgDir, 'source', 'union-to-intersection.d.ts');
  const content = fs.readFileSync(u2iDtsPath, 'utf8');
  assert.ok(
    content.includes('Union extends unknown'),
    'UnionToIntersection must use distributive conditional type over Union'
  );
  assert.ok(
    content.includes('? (distributedUnion: Union) => void'),
    'UnionToIntersection must distribute union as function argument'
  );
  assert.ok(
    content.includes('extends ((mergedIntersection: infer Intersection) => void)'),
    'UnionToIntersection must infer Intersection from function parameter'
  );
  assert.ok(
    content.includes('? Intersection'),
    'UnionToIntersection must return inferred Intersection'
  );
}

// Contract 5: UnionToIntersection documentation provides usage examples demonstrating union object types merged into single intersection
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const u2iDtsPath = path.join(pkgDir, 'source', 'union-to-intersection.d.ts');
  const content = fs.readFileSync(u2iDtsPath, 'utf8');
  assert.ok(
    content.includes('type Intersection = UnionToIntersection<Union>;'),
    'UnionToIntersection must document type usage example'
  );
  assert.ok(
    content.includes('Convert a union type to an intersection type'),
    'UnionToIntersection must document purpose in JSDoc'
  );
}

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