yaml 2.9.0: visit, visitAsync

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 pkg:npm/yaml@2.9.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/yaml@2.9.0
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@11.8.0
  - runtime: node@22.22.2

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:c364dd243b5cecbd867c1066b749a08c7803c549c992fbaed3b59e89b189e7c6","constraints":{"executionContext":"node"},"contract":["assert visit traverses AST nodes and mutates scalar values in-place within a YAML Document","assert visit removes mapping pairs and sequence items when returning visit.REMOVE","assert visit replaces AST nodes when returning a new Scalar from visitor callback","assert visit stops further traversal immediately when returning visit.BREAK","assert visit skips child node traversal when returning visit.SKIP","assert visitAsync asynchronously traverses and mutates Document AST nodes with async visitor callbacks"],"goal":"verify pkg:npm/yaml@2.9.0","kind":"HOW","packages":["pkg:npm/yaml@2.9.0"],"schemaVersion":1,"symbols":["yaml.visit","yaml.visitAsync"]},"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":"11.8.0","runtime":"node","runtimeVersion":"22.22.2","schemaVersion":1,"virtualization":"wsl"},"license":"MIT-0","packages":["pkg:npm/yaml@2.9.0"],"schemaVersion":1,"symbols":["yaml.visit","yaml.visitAsync"],"verifierAdapter":"node-typescript@1"}

import YAML, { parseDocument, visit, visitAsync, Scalar } from 'yaml';

/**
 * Traverse and modify a YAML Document AST using visit.
 */
export function walkDocument(doc, visitor) {
  visit(doc, visitor);
  return doc;
}

/**
 * Remove nodes matching a predicate by returning visit.REMOVE.
 */
export function removeMatchingNodes(doc, predicate) {
  visit(doc, {
    Pair(key, pair) {
      if (predicate('Pair', pair)) {
        return visit.REMOVE;
      }
    },
    Seq(key, seq) {
      if (predicate('Seq', seq)) {
        return visit.REMOVE;
      }
    },
    Scalar(key, scalar) {
      if (predicate('Scalar', scalar)) {
        return visit.REMOVE;
      }
    }
  });
  return doc;
}

/**
 * Replace scalar values in AST using visitor return values.
 */
export function replaceScalarValues(doc, replacer) {
  visit(doc, {
    Scalar(key, scalar) {
      const replacement = replacer(scalar.value, key);
      if (replacement !== undefined && replacement !== scalar.value) {
        return new Scalar(replacement);
      }
    }
  });
  return doc;
}

/**
 * Asynchronously traverse and modify a YAML Document AST using visitAsync.
 */
export async function walkDocumentAsync(doc, asyncVisitor) {
  await visitAsync(doc, asyncVisitor);
  return doc;
}

{
  "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==",
      "license": "ISC",
      "bin": {
        "yaml": "bin.mjs"
      },
      "engines": {
        "node": ">= 14.6"
      },
      "funding": {
        "url": "https://github.com/sponsors/eemeli"
      }
    }
  }
}

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

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/yaml@2.9.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/yaml@2.9.0"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@11.8.0",
    "runtime": "node@22.22.2"
  }
}

import assert from 'node:assert/strict';
import YAML, { parseDocument, visit, visitAsync, Scalar } from 'yaml';
import {
  walkDocument,
  removeMatchingNodes,
  replaceScalarValues,
  walkDocumentAsync
} from '../index.mjs';

// 1. assert visit traverses AST nodes and mutates scalar values in-place within a YAML Document
{
  const yamlSource = `
app:
  name: demo-service
  environment: staging
  port: 3000
`;
  const doc = parseDocument(yamlSource);
  walkDocument(doc, {
    Scalar(key, node) {
      if (node.value === 'staging') {
        node.value = 'production';
      }
      if (node.value === 3000) {
        node.value = 8080;
      }
    }
  });

  const js = doc.toJS();
  assert.equal(js.app.name, 'demo-service');
  assert.equal(js.app.environment, 'production');
  assert.equal(js.app.port, 8080);
}

// 2. assert visit removes mapping pairs and sequence items when returning visit.REMOVE
{
  const yamlSource = `
service:
  name: web-api
  secretKey: confidential-token
tags:
  - public
  - internal-only
  - release
`;
  const doc = parseDocument(yamlSource);
  removeMatchingNodes(doc, (type, node) => {
    if (type === 'Pair' && node.key && node.key.value === 'secretKey') {
      return true;
    }
    if (type === 'Scalar' && node.value === 'internal-only') {
      return true;
    }
    return false;
  });

  const js = doc.toJS();
  assert.equal(js.service.name, 'web-api');
  assert.equal(js.service.secretKey, undefined);
  assert.deepEqual(js.tags, ['public', 'release']);
}

// 3. assert visit replaces AST nodes when returning a new Scalar from visitor callback
{
  const yamlSource = `
database:
  host: localhost
  timeout: 5
`;
  const doc = parseDocument(yamlSource);
  replaceScalarValues(doc, (val, key) => {
    if (val === 'localhost') {
      return 'db.internal';
    }
    if (val === 5) {
      return 30;
    }
    return val;
  });

  const js = doc.toJS();
  assert.equal(js.database.host, 'db.internal');
  assert.equal(js.database.timeout, 30);
}

// 4. assert visit stops further traversal immediately when returning visit.BREAK
{
  const yamlSource = `
step1: alpha
step2: beta
step3: gamma
step4: delta
`;
  const doc = parseDocument(yamlSource);
  const visitedValues = [];
  visit(doc, {
    Scalar(key, node) {
      visitedValues.push(node.value);
      if (node.value === 'beta') {
        return visit.BREAK;
      }
    }
  });

  assert.ok(visitedValues.includes('step1'));
  assert.ok(visitedValues.includes('alpha'));
  assert.ok(visitedValues.includes('step2'));
  assert.ok(visitedValues.includes('beta'));
  assert.equal(visitedValues.includes('step3'), false);
  assert.equal(visitedValues.includes('gamma'), false);
  assert.equal(visitedValues.includes('step4'), false);
  assert.equal(visitedValues.includes('delta'), false);
}

// 5. assert visit skips child node traversal when returning visit.SKIP
{
  const yamlSource = `
included:
  nestedKey: nestedVal
skippedSection:
  nestedKey: secretVal
`;
  const doc = parseDocument(yamlSource);
  const visitedKeys = [];
  visit(doc, {
    Pair(key, pair) {
      if (pair.key && pair.key.value === 'skippedSection') {
        return visit.SKIP;
      }
    },
    Scalar(key, node) {
      visitedKeys.push(node.value);
    }
  });

  assert.deepEqual(visitedKeys, ['included', 'nestedKey', 'nestedVal']);
}

// 6. assert visitAsync asynchronously traverses and mutates Document AST nodes with async visitor callbacks
{
  const yamlSource = `
metrics:
  cpu: 10
  memory: 20
  disk: 30
`;
  const doc = parseDocument(yamlSource);
  await walkDocumentAsync(doc, {
    async Scalar(key, node) {
      if (typeof node.value === 'number') {
        await new Promise((resolve) => setTimeout(resolve, 5));
        node.value = node.value * 2;
      }
    }
  });

  const js = doc.toJS();
  assert.equal(js.metrics.cpu, 20);
  assert.equal(js.metrics.memory, 40);
  assert.equal(js.metrics.disk, 60);
}

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