yaml 2.9.0: Parse and stringify YAML documents preserving and modifying AST nodes with YAML.parseDocument and doc.set

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: Parse and stringify YAML documents preserving and modifying AST nodes with YAML.parseDocument and doc.set
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/yaml@2.9.0

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:sha256:5e96f7d9e04ca061bd783588d6416a49a09da4ba20bbc0e759762b45fd9aa956","contract":["assert YAML.parseDocument parses YAML content into a Document AST preserving document structure","assert Document.get and Document.set read and mutate top-level mappings and scalars","assert Document.getIn and Document.setIn navigate and modify nested object and array paths","assert Document.hasIn checks path presence and Document.deleteIn removes nested keys and array items","assert Document AST retains comments and custom formatting when mutating values and stringifying","assert Document.toJS converts manipulated AST structures into standard JavaScript objects","assert YAML.parseDocument captures errors on malformed YAML syntax without throwing immediately"],"goal":"Parse and stringify YAML documents preserving and modifying AST nodes with YAML.parseDocument and doc.set","kind":"HOW","packages":["pkg:npm/yaml@2.9.0"],"schemaVersion":1,"symbols":["YAML.parseDocument","Document.get","Document.set","Document.getIn","Document.setIn","Document.deleteIn","Document.hasIn","Document.toJS","Document.toString"]},"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,"virtualization":"wsl"},"license":"MIT-0","packages":["pkg:npm/yaml@2.9.0"],"schemaVersion":1,"symbols":["YAML.parseDocument","Document.get","Document.set","Document.getIn","Document.setIn","Document.deleteIn","Document.hasIn","Document.toJS","Document.toString"],"verifierAdapter":"node-typescript@1"}

import YAML from 'yaml';

/**
 * Parse a YAML string into a Document AST.
 */
export function parseDoc(text, options = {}) {
  return YAML.parseDocument(text, options);
}

/**
 * Get a value at a given path in the document.
 */
export function getPath(doc, path) {
  return doc.getIn(Array.isArray(path) ? path : [path]);
}

/**
 * Set a value at a given path in the document.
 */
export function setPath(doc, path, value) {
  doc.setIn(Array.isArray(path) ? path : [path], value);
  return doc;
}

/**
 * Delete a value at a given path in the document.
 */
export function deletePath(doc, path) {
  return doc.deleteIn(Array.isArray(path) ? path : [path]);
}

/**
 * Check if a given path exists in the document.
 */
export function hasPath(doc, path) {
  return doc.hasIn(Array.isArray(path) ? path : [path]);
}

/**
 * Stringify the YAML document back to string.
 */
export function stringifyDoc(doc, options = {}) {
  return doc.toString(options);
}

{
  "name": "sample",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample",
      "version": "1.0.0",
      "dependencies": {
        "yaml": "2.9.0"
      }
    },
    "node_modules/yaml": {
      "version": "2.9.0",
      "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.9.0.tgz",
      "integrity": "sha512-2AvhNX3mb8zd6Zy7INTtSpl1F15HW6Wnqj0srWlkKLcpYl/gMIMJiyuGq2KeI2YFxUPjdlB+3Lc10seMLtL4cA=="
    }
  }
}

{
  "name": "sample",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "yaml": "2.9.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "Parse and stringify YAML documents preserving and modifying AST nodes with YAML.parseDocument and doc.set",
  "kind": "HOW",
  "packages": [
    "pkg:npm/yaml@2.9.0"
  ]
}

import assert from 'node:assert/strict';
import YAML from 'yaml';
import {
  parseDoc,
  getPath,
  setPath,
  deletePath,
  hasPath,
  stringifyDoc
} from '../index.mjs';

// 1. assert YAML.parseDocument parses YAML content into a Document AST preserving document structure
{
  const yamlText = `
name: web-service
version: 1.0.0
tags:
  - web
  - api
`;
  const doc = parseDoc(yamlText);
  assert.ok(doc instanceof YAML.Document);
  assert.equal(doc.errors.length, 0);
  assert.equal(doc.get('name'), 'web-service');
  assert.equal(doc.get('version'), '1.0.0');
  assert.deepEqual(doc.toJS().tags, ['web', 'api']);
}

// 2. assert Document.get and Document.set read and mutate top-level mappings and scalars
{
  const doc = parseDoc('title: original\ncount: 5\n');
  assert.equal(doc.get('title'), 'original');
  assert.equal(doc.get('count'), 5);

  doc.set('title', 'updated');
  doc.set('count', 10);
  doc.set('active', true);

  assert.equal(doc.get('title'), 'updated');
  assert.equal(doc.get('count'), 10);
  assert.equal(doc.get('active'), true);
  assert.deepEqual(doc.toJS(), {
    title: 'updated',
    count: 10,
    active: true
  });
}

// 3. assert Document.getIn and Document.setIn navigate and modify nested object and array paths
{
  const yamlText = `
server:
  host: 127.0.0.1
  ports:
    - 80
    - 443
database:
  connection:
    pool: 10
`;
  const doc = parseDoc(yamlText);

  assert.equal(getPath(doc, ['server', 'host']), '127.0.0.1');
  assert.equal(getPath(doc, ['server', 'ports', 0]), 80);
  assert.equal(getPath(doc, ['database', 'connection', 'pool']), 10);

  setPath(doc, ['server', 'ports', 0], 8080);
  setPath(doc, ['database', 'connection', 'pool'], 25);
  setPath(doc, ['server', 'tls', 'enabled'], true);

  assert.equal(getPath(doc, ['server', 'ports', 0]), 8080);
  assert.equal(getPath(doc, ['database', 'connection', 'pool']), 25);
  assert.equal(getPath(doc, ['server', 'tls', 'enabled']), true);

  const js = doc.toJS();
  assert.deepEqual(js.server.ports, [8080, 443]);
  assert.equal(js.database.connection.pool, 25);
  assert.equal(js.server.tls.enabled, true);
}

// 4. assert Document.hasIn checks path presence and Document.deleteIn removes nested keys and array items
{
  const yamlText = `
config:
  debug: true
  temp: /tmp
  items:
    - keep
    - remove_me
`;
  const doc = parseDoc(yamlText);

  assert.equal(hasPath(doc, ['config', 'debug']), true);
  assert.equal(hasPath(doc, ['config', 'nonexistent']), false);
  assert.equal(hasPath(doc, ['config', 'items', 1]), true);

  const deletedKey = deletePath(doc, ['config', 'temp']);
  assert.equal(deletedKey, true);
  assert.equal(hasPath(doc, ['config', 'temp']), false);

  const deletedItem = deletePath(doc, ['config', 'items', 1]);
  assert.equal(deletedItem, true);

  const js = doc.toJS();
  assert.deepEqual(js.config, {
    debug: true,
    items: ['keep']
  });
}

// 5. assert Document AST retains comments and custom formatting when mutating values and stringifying
{
  const yamlText = `# Service configuration
service:
  # Port for HTTP traffic
  port: 8080
  name: test-app # inline comment
`;
  const doc = parseDoc(yamlText);
  doc.setIn(['service', 'port'], 9000);

  const output = stringifyDoc(doc);
  assert.ok(output.includes('# Service configuration'));
  assert.ok(output.includes('# Port for HTTP traffic'));
  assert.ok(output.includes('port: 9000'));
  assert.ok(output.includes('# inline comment'));
}

// 6. assert Document.toJS converts manipulated AST structures into standard JavaScript objects
{
  const doc = new YAML.Document({
    appName: 'sample-service',
    endpoints: ['/health', '/metrics'],
    retries: 3
  });

  doc.set('version', '2.0.0');
  const js = doc.toJS();

  assert.equal(typeof js, 'object');
  assert.equal(js.appName, 'sample-service');
  assert.deepEqual(js.endpoints, ['/health', '/metrics']);
  assert.equal(js.retries, 3);
  assert.equal(js.version, '2.0.0');
}

// 7. assert YAML.parseDocument captures errors on malformed YAML syntax without throwing immediately
{
  const malformedYaml = `
key: [unterminated list
  nested: value: invalid
`;
  const doc = YAML.parseDocument(malformedYaml);
  assert.ok(doc.errors.length > 0);
  assert.ok(doc.errors[0] instanceof YAML.YAMLParseError);
}

console.log('PASS: all contract assertions satisfied');