postcss-value-parser 4.2.0: ValueParser.walk

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 ValueParser.walk in pkg:npm/postcss-value-parser@4.2.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/postcss-value-parser@4.2.0
Demonstrate these symbols/APIs:
  - ValueParser.walk

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:sha256:793ba64884dab9bfbbd8dfccf146d1267454ac31ace2a0f8e028b89e0e1e138a","contract":["ValueParser.walk iterates top-down by default, passing (node, index, nodes) to the callback","Returning false from the callback prevents walk from descending into child nodes of a function node","Setting bubble to true causes walk to traverse child nodes before visiting their parent function node","ValueParser instance walk method traverses parsed nodes and returns the instance for method chaining","Mutating node values during walk alters the AST and updates the serialized string representation"],"goal":"verify ValueParser.walk in pkg:npm/postcss-value-parser@4.2.0","kind":"HOW","packages":["pkg:npm/postcss-value-parser@4.2.0"],"schemaVersion":1,"symbols":["ValueParser.walk"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/postcss-value-parser@4.2.0"],"schemaVersion":1,"subject":"pkg:npm/postcss-value-parser@4.2.0","symbols":["ValueParser.walk"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-postcss-value-parser",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-postcss-value-parser",
      "version": "1.0.0",
      "dependencies": {
        "postcss-value-parser": "4.2.0"
      }
    },
    "node_modules/postcss-value-parser": {
      "version": "4.2.0",
      "resolved": "https://registry.npmjs.org/postcss-value-parser/-/postcss-value-parser-4.2.0.tgz",
      "integrity": "sha512-1NNCs6uurfkVbeXG4S8JFT9t19m45ICnif8zWLd5oPSZ50QnwMfK+H3jv408d4jw/7Bttv5axS5IiHoLaVNHeQ==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-postcss-value-parser",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "dependencies": {
    "postcss-value-parser": "4.2.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify ValueParser.walk in pkg:npm/postcss-value-parser@4.2.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/postcss-value-parser@4.2.0"
  ],
  "symbols": [
    "ValueParser.walk"
  ]
}

import assert from 'node:assert/strict';
import valueParser from 'postcss-value-parser';

// 1. ValueParser.walk iterates top-down by default, passing (node, index, nodes) to the callback
{
  const parsed = valueParser('calc(10px + 20px) url(image.png)');
  const visited = [];
  const indices = [];

  valueParser.walk(parsed.nodes, (node, index, nodes) => {
    visited.push({ type: node.type, value: node.value });
    indices.push(index);
    assert.ok(Array.isArray(nodes));
    assert.strictEqual(nodes[index], node);
  });

  assert.deepStrictEqual(visited, [
    { type: 'function', value: 'calc' },
    { type: 'word', value: '10px' },
    { type: 'space', value: ' ' },
    { type: 'word', value: '+' },
    { type: 'space', value: ' ' },
    { type: 'word', value: '20px' },
    { type: 'space', value: ' ' },
    { type: 'function', value: 'url' },
    { type: 'word', value: 'image.png' }
  ]);
  assert.deepStrictEqual(indices, [0, 0, 1, 2, 3, 4, 1, 2, 0]);
}

// 2. Returning false from the callback prevents walk from descending into child nodes of a function node
{
  const parsed = valueParser('calc(10px + 20px) var(--main-color)');
  const visited = [];

  valueParser.walk(parsed.nodes, (node) => {
    visited.push(node.value);
    if (node.type === 'function' && node.value === 'calc') {
      return false;
    }
  });

  assert.deepStrictEqual(visited, [
    'calc',
    ' ',
    'var',
    '--main-color'
  ]);
}

// 3. Setting bubble to true causes walk to traverse child nodes before visiting their parent function node
{
  const parsed = valueParser('rgba(255, 0, 0, 0.5)');
  const visited = [];

  valueParser.walk(parsed.nodes, (node) => {
    visited.push({ type: node.type, value: node.value });
  }, true);

  assert.deepStrictEqual(visited, [
    { type: 'word', value: '255' },
    { type: 'div', value: ',' },
    { type: 'word', value: '0' },
    { type: 'div', value: ',' },
    { type: 'word', value: '0' },
    { type: 'div', value: ',' },
    { type: 'word', value: '0.5' },
    { type: 'function', value: 'rgba' }
  ]);
}

// 4. ValueParser instance walk method traverses parsed nodes and returns the instance for method chaining
{
  const parsed = valueParser('linear-gradient(to right, red, blue)');
  const visited = [];

  const returned = parsed.walk((node) => {
    if (node.type === 'word') {
      visited.push(node.value);
    }
  });

  assert.strictEqual(returned, parsed);
  assert.deepStrictEqual(visited, ['to', 'right', 'red', 'blue']);
}

// 5. Mutating node values during walk alters the AST and updates the serialized string representation
{
  const parsed = valueParser('border-box 10px 20px');

  parsed.walk((node) => {
    if (node.type === 'word' && node.value.endsWith('px')) {
      const num = parseInt(node.value, 10);
      node.value = `${num * 2}px`;
    }
  });

  assert.strictEqual(parsed.toString(), 'border-box 20px 40px');
}