type-fest 0.13.1: ConditionalKeys

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.ConditionalKeys 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.ConditionalKeys

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:sha256:5d0c3ba9800ab13abf3c47cdf830875f8a14c62b8e89210ff2f875ed594e403c","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 ConditionalKeys symbol from source/conditional-keys","ConditionalKeys type definition maps keys of base type to keys whose value type extends the condition","ConditionalKeys wraps the mapped keys union in NonNullable to strip undefined","ConditionalKeys resolves never for keys that do not extend the condition"],"goal":"verify type-fest.ConditionalKeys in pkg:npm/type-fest@0.13.1","kind":"HOW","packages":["pkg:npm/type-fest@0.13.1"],"schemaVersion":1,"symbols":["type-fest.ConditionalKeys"]},"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.ConditionalKeys"],"verifierAdapter":"node-typescript@1"}

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

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

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 ConditionalKeys symbol from source/conditional-keys
{
  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 {ConditionalKeys} from './source/conditional-keys';"),
    'ConditionalKeys must be exported from index.d.ts'
  );
}

// Contract 3: ConditionalKeys type definition maps keys of base type to keys whose value type extends the condition
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const condKeysDtsPath = path.join(pkgDir, 'source', 'conditional-keys.d.ts');
  assert.ok(fs.existsSync(condKeysDtsPath), 'source/conditional-keys.d.ts must exist');
  const condKeysContent = fs.readFileSync(condKeysDtsPath, 'utf8');
  assert.ok(
    condKeysContent.includes('export type ConditionalKeys<Base, Condition> = NonNullable<'),
    'ConditionalKeys must declare generic Base and Condition parameters wrapped in NonNullable'
  );
  assert.ok(
    condKeysContent.includes('[Key in keyof Base]:'),
    'ConditionalKeys must map through all keys of Base'
  );
  assert.ok(
    condKeysContent.includes('Base[Key] extends Condition'),
    'ConditionalKeys must test whether Base[Key] extends Condition'
  );
}

// Contract 4: ConditionalKeys wraps the mapped keys union in NonNullable to strip undefined
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const condKeysDtsPath = path.join(pkgDir, 'source', 'conditional-keys.d.ts');
  const condKeysContent = fs.readFileSync(condKeysDtsPath, 'utf8');
  assert.ok(
    condKeysContent.includes('}[keyof Base]'),
    'ConditionalKeys must index mapped type with keyof Base to produce a union'
  );
  assert.ok(
    condKeysContent.includes('NonNullable<'),
    'ConditionalKeys must wrap mapped type in NonNullable'
  );
}

// Contract 5: ConditionalKeys resolves never for keys that do not extend the condition
{
  const pkgDir = path.dirname(require.resolve('type-fest/package.json'));
  const condKeysDtsPath = path.join(pkgDir, 'source', 'conditional-keys.d.ts');
  const condKeysContent = fs.readFileSync(condKeysDtsPath, 'utf8');
  assert.ok(
    condKeysContent.includes('? Key'),
    'ConditionalKeys must retain key when condition passes'
  );
  assert.ok(
    condKeysContent.includes(': never;'),
    'ConditionalKeys must discard key by resolving to never when condition fails'
  );
}

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