browserslist 4.28.7: findConfig

# browserslist.findConfig Behavior

## Pinned Release
- `browserslist`: `4.28.7` (resolved via `npm`)
- Runtime: Node.js (tested on Node 22 ESM)

## Observed Behavior & Contract Details

### 1. Configuration Discovery (`findConfig`)
- `browserslist.findConfig(path)` searches upward for `.browserslistrc` or `package.json` with a `browserslist` property.
- When discovering `.browserslistrc`, it returns structured section mappings (`{ defaults: [...], ...sections }`).
- When discovering `package.json` with an array `browserslist`, it wraps queries under `{ defaults: [...] }`.
- When discovering `package.json` with an object `browserslist`, it returns section mappings directly without inserting a `defaults` array.
- When no configuration file exists in the directory hierarchy, it returns `undefined`.

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 browserslist.findConfig in pkg:npm/browserslist@4.28.7
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/browserslist@4.28.7
Demonstrate these symbols/APIs:
  - browserslist.findConfig

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:sha256:29c791479ec8ea30263ea29c601ad47f3c537abc0ba0232ab5375e85534ce067","contract":["browserslist.findConfig(dir) discovers .browserslistrc files and returns structured section mappings","browserslist.findConfig(dir) discovers package.json browserslist array configurations and wraps them under defaults","browserslist.findConfig(dir) discovers package.json browserslist object configurations without adding defaults","browserslist.findConfig(dir) returns undefined when no configuration file exists in the directory tree"],"goal":"verify browserslist.findConfig in pkg:npm/browserslist@4.28.7","kind":"HOW","packages":["pkg:npm/browserslist@4.28.7"],"schemaVersion":1,"symbols":["browserslist.findConfig"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/browserslist@4.28.7"],"schemaVersion":1,"subject":"pkg:npm/browserslist@4.28.7","symbols":["browserslist.findConfig"],"verifierAdapter":"node-typescript@1"}

{
  "name": "verify-browserslist-findconfig",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "verify-browserslist-findconfig",
      "version": "1.0.0",
      "dependencies": {
        "browserslist": "4.28.7"
      }
    },
    "node_modules/baseline-browser-mapping": {
      "version": "2.11.24",
      "resolved": "https://registry.npmjs.org/baseline-browser-mapping/-/baseline-browser-mapping-2.11.24.tgz",
      "integrity": "sha512-hYrgxie335U08WqICoGqKRzV1HFXv6zdxwJE4ekCb80CM9a0SVVsN4QPwT67RraRo+9h8IATk6uxHJw7QSkdOg==",
      "license": "Apache-2.0",
      "bin": {
        "baseline-browser-mapping": "dist/cli.cjs"
      },
      "engines": {
        "node": ">=6.0.0"
      }
    },
    "node_modules/browserslist": {
      "version": "4.28.7",
      "resolved": "https://registry.npmjs.org/browserslist/-/browserslist-4.28.7.tgz",
      "integrity": "sha512-JxV13hNrFxqjOc8alRbq9dK1MM79NEXYpma2B2J4wAtpWS5zIEIKqWPGCl7N4o7Uc7B7itylh7SuDujATRyyTw==",
      "funding": [
        {
          "type": "opencollective",
          "url": "https://opencollective.com/browserslist"
        },
        {
          "type": "tidelift",
          "url": "https://tidelift.com/funding/github/npm/browserslist"
        },
        {
          "type": "github",
          "url": "https://github.com/sponsors/ai"
        }
      ],
      "license": "MIT",
      "dependencies": {
        "baseline-browser-mapping": "^2.10.44",
        "caniuse-lite": "^1.0.30001806",
        "electron-to-chromium": "^1.5.393",
        "node-releases": "^2.0.51",
        "update-browserslist-db": "^1.2.3"
      },
      "bin": {
        "browserslist": "cli.js"
      },
      "engines": {
        "node": "^6 || ^7 || ^8 || ^9 || ^10 || ^11 || ^12 || >=13.7"
      }
    },
    "node_modules/caniuse-lite": {
      "version": "1.0.30001810",
      "resolved": "https://registry.npmjs.org/caniuse-lite/-/caniuse-lite-1.0.30001810.tgz",
      "integrity": "sha512-TITQPUkaz+aVk5GL6NhOdwk1aEaNTSDPsGFWrTuhKGtjTF70jL/Oht2W4c6rXUe5fu7Ie19VIahAXHIIiWWNeg==",
      "funding": [
        {
          "type": "opencollective",
          "url": "https://opencollective.com/browserslist"
        },
        {
          "type": "tidelift",
          "url": "https://tidelift.com/funding/github/npm/caniuse-lite"
        },
        {
          "type": "github",
          "url": "https://github.com/sponsors/ai"
        }
      ],
      "license": "CC-BY-4.0"
    },
    "node_modules/electron-to-chromium": {
      "version": "1.5.430",
      "resolved": "https://registry.npmjs.org/electron-to-chromium/-/electron-to-chromium-1.5.430.tgz",
      "integrity": "sha512-e1QEj72Y4zd8RlNZVmoTg+iCOSVwpk05IOiiQwdrkwCSVlZfPthevErhE+nckGd2YbsXfp1SkisznhGVIXP2NQ==",
      "license": "ISC"
    },
    "node_modules/escalade": {
      "version": "3.2.0",
      "resolved": "https://registry.npmjs.org/escalade/-/escalade-3.2.0.tgz",
      "integrity": "sha512-WUj2qlxaQtO4g6Pq5c29GTcWGDyd8itL8zTlipgECz3JesAiiOKotd8JU6otB3PACgG6xkJUyVhboMS+bje/jA==",
      "license": "MIT",
      "engines": {
        "node": ">=6"
      }
    },
    "node_modules/node-releases": {
      "version": "2.0.55",
      "resolved": "https://registry.npmjs.org/node-releases/-/node-releases-2.0.55.tgz",
      "integrity": "sha512-mIrE/Cw9y+9Au6dS5vDKDhQza9YvG6w+ZrS6X+ZzA7yFW/soAeaups4Qzn1bL6g5FVy8WtP79+0j82oPIbqRjQ==",
      "license": "MIT",
      "engines": {
        "node": ">=18"
      }
    },
    "node_modules/picocolors": {
      "version": "1.1.1",
      "resolved": "https://registry.npmjs.org/picocolors/-/picocolors-1.1.1.tgz",
      "integrity": "sha512-xceH2snhtb5M9liqDsmEw56le376mTZkEX/jEb/RxNFyegNul7eNslCXP9FDj/Lcu0X8KEyMceP2ntpaHrDEVA==",
      "license": "ISC"
    },
    "node_modules/update-browserslist-db": {
      "version": "1.3.3",
      "resolved": "https://registry.npmjs.org/update-browserslist-db/-/update-browserslist-db-1.3.3.tgz",
      "integrity": "sha512-pJ2sYawQS0R/WI928Gj5GlPhTGzbMelq0+4INtSYNDV9ErKJcX6xjGWkoG/VnB3dpUm00zALaqkrUD77pO5TDQ==",
      "funding": [
        {
          "type": "opencollective",
          "url": "https://opencollective.com/browserslist"
        },
        {
          "type": "tidelift",
          "url": "https://tidelift.com/funding/github/npm/browserslist"
        },
        {
          "type": "github",
          "url": "https://github.com/sponsors/ai"
        }
      ],
      "license": "MIT",
      "dependencies": {
        "escalade": "^3.2.0",
        "picocolors": "^1.1.1"
      },
      "bin": {
        "update-browserslist-db": "cli.js"
      },
      "peerDependencies": {
        "browserslist": ">= 4.21.0"
      }
    }
  }
}

{
  "name": "verify-browserslist-findconfig",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "dependencies": {
    "browserslist": "4.28.7"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify browserslist.findConfig in pkg:npm/browserslist@4.28.7",
  "kind": "HOW",
  "packages": [
    "pkg:npm/browserslist@4.28.7"
  ],
  "symbols": [
    "browserslist.findConfig"
  ]
}

import assert from 'node:assert/strict';
import fs from 'node:fs';
import path from 'node:path';
import os from 'node:os';
import browserslist from 'browserslist';

const tempBase = fs.mkdtempSync(path.join(os.tmpdir(), 'csx-browserslist-findconfig-'));

try {
  const rcDir = path.join(tempBase, 'rc-project');
  fs.mkdirSync(rcDir, { recursive: true });
  fs.writeFileSync(
    path.join(rcDir, '.browserslistrc'),
    '[production]\nchrome >= 100\n\n[development]\nlast 1 chrome version\n'
  );

  const pkgArrayDir = path.join(tempBase, 'pkg-array-project');
  fs.mkdirSync(pkgArrayDir, { recursive: true });
  fs.writeFileSync(
    path.join(pkgArrayDir, 'package.json'),
    JSON.stringify({ browserslist: ['> 1%', 'not dead'] })
  );

  const pkgObjDir = path.join(tempBase, 'pkg-obj-project');
  fs.mkdirSync(pkgObjDir, { recursive: true });
  fs.writeFileSync(
    path.join(pkgObjDir, 'package.json'),
    JSON.stringify({
      browserslist: {
        production: ['> 0.5%'],
        development: ['last 1 chrome version']
      }
    })
  );

  const emptyDir = path.join(tempBase, 'empty-project');
  fs.mkdirSync(emptyDir, { recursive: true });

  // 1. browserslist.findConfig(dir) discovers .browserslistrc files and returns structured section mappings
  const foundRc = browserslist.findConfig(rcDir);
  assert.deepStrictEqual(foundRc, {
    defaults: [],
    production: ['chrome >= 100'],
    development: ['last 1 chrome version']
  });

  // 2. browserslist.findConfig(dir) discovers package.json browserslist array configurations and wraps them under defaults
  const foundPkgArray = browserslist.findConfig(pkgArrayDir);
  assert.deepStrictEqual(foundPkgArray, {
    defaults: ['> 1%', 'not dead']
  });

  // 3. browserslist.findConfig(dir) discovers package.json browserslist object configurations without adding defaults
  const foundPkgObj = browserslist.findConfig(pkgObjDir);
  assert.deepStrictEqual(foundPkgObj, {
    production: ['> 0.5%'],
    development: ['last 1 chrome version']
  });

  // 4. browserslist.findConfig(dir) returns undefined when no configuration file exists in the directory tree
  const foundNone = browserslist.findConfig(emptyDir);
  assert.strictEqual(foundNone, undefined);

  console.log('Contract passed successfully.');
} finally {
  fs.rmSync(tempBase, { recursive: true, force: true });
}