@jridgewell/sourcemap-codec 1.5.5: decode

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 decode in pkg:npm/%40jridgewell/sourcemap-codec@1.5.5
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40jridgewell/sourcemap-codec@1.5.5
Demonstrate these symbols/APIs:
  - decode
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:81f0faf1b464181eeaefbbdcf4792f96fec9065b0a3a762464e573b86734aad8","constraints":{"executionContext":"node"},"contract":["decode parses empty mappings string to a single empty line array","decode parses 1-element segment containing generated column offset","decode parses 4-element segment containing generated column, source index, original line, and original column","decode parses 5-element segment containing generated column, source index, original line, original column, and name index","decode parses comma-separated segments within the same line","decode parses semicolon-separated lines and preserves empty lines"],"goal":"verify decode in pkg:npm/%40jridgewell/sourcemap-codec@1.5.5","kind":"HOW","packages":["pkg:npm/%40jridgewell/sourcemap-codec@1.5.5"],"schemaVersion":1,"symbols":["decode"]},"contractCommand":["node","test/contract.js"],"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/%40jridgewell/sourcemap-codec@1.5.5"],"schemaVersion":1,"subject":"pkg:npm/%40jridgewell/sourcemap-codec@1.5.5","symbols":["decode"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-sourcemap-codec",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-sourcemap-codec",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "@jridgewell/sourcemap-codec": "1.5.5"
      }
    },
    "node_modules/@jridgewell/sourcemap-codec": {
      "version": "1.5.5",
      "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz",
      "integrity": "sha512-cYQ9310grqxueWbl+WuIUIaiUaDcj7WOq5fVhEljNVgRfOUhY9fy2zTvfoqWsnebh8Sl70VScFbICvJnLKB0Og==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-sourcemap-codec",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification sample for @jridgewell/sourcemap-codec",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "@jridgewell/sourcemap-codec": "1.5.5"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify decode in pkg:npm/%40jridgewell/sourcemap-codec@1.5.5",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40jridgewell/sourcemap-codec@1.5.5"
  ],
  "symbols": [
    "decode"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

const { decode } = require('@jridgewell/sourcemap-codec');

/**
 * Decode a source map mappings string into an array of lines containing segments.
 *
 * @param {string} mappings
 * @returns {number[][][]}
 */
function decodeMappings(mappings) {
  return decode(mappings);
}

/**
 * Decode mappings and convert raw segment tuples into structured objects.
 *
 * @param {string} mappings
 * @returns {Array<Array<{ generatedColumn: number, sourceIndex?: number, originalLine?: number, originalColumn?: number, nameIndex?: number }>>}
 */
function decodeToStructured(mappings) {
  const decoded = decode(mappings);
  return decoded.map((line) =>
    line.map((segment) => {
      const obj = { generatedColumn: segment[0] };
      if (segment.length >= 4) {
        obj.sourceIndex = segment[1];
        obj.originalLine = segment[2];
        obj.originalColumn = segment[3];
      }
      if (segment.length >= 5) {
        obj.nameIndex = segment[4];
      }
      return obj;
    })
  );
}

/**
 * Count total number of mapping segments across all lines.
 *
 * @param {string} mappings
 * @returns {number}
 */
function countSegments(mappings) {
  const decoded = decode(mappings);
  return decoded.reduce((acc, line) => acc + line.length, 0);
}

module.exports = {
  decodeMappings,
  decodeToStructured,
  countSegments
};

const assert = require('node:assert');
const { decode } = require('@jridgewell/sourcemap-codec');
const {
  decodeMappings,
  decodeToStructured,
  countSegments
} = require('../src/index.js');

// 1. Empty mappings string
const emptyResult = decode('');
assert.deepStrictEqual(emptyResult, [[]], 'empty mappings should return single empty line array');
assert.deepStrictEqual(decodeMappings(''), [[]], 'decodeMappings helper handles empty mappings');
assert.strictEqual(countSegments(''), 0, 'countSegments on empty mappings returns 0');

// 2. Single 1-element segment (generated column only: [generatedColumn])
// "K" in VLQ is 5
const singleCol = decode('K');
assert.deepStrictEqual(singleCol, [[[5]]], 'decode single 1-element segment');

// 3. Single 4-element segment: [genCol, sourceIndex, origLine, origCol]
// "AAAA" decodes to [0, 0, 0, 0]
const single4Tuple = decode('AAAA');
assert.deepStrictEqual(single4Tuple, [[[0, 0, 0, 0]]], 'decode single 4-element segment');

// 4. Single 5-element segment: [genCol, sourceIndex, origLine, origCol, nameIndex]
// "AAAAA" decodes to [0, 0, 0, 0, 0]
const single5Tuple = decode('AAAAA');
assert.deepStrictEqual(single5Tuple, [[[0, 0, 0, 0, 0]]], 'decode single 5-element segment');

// 5. Multiple segments on the same line (comma separated)
// "AAAA,CAAC" -> [0,0,0,0], [1,0,0,1]
const multiSegments = decode('AAAA,CAAC');
assert.deepStrictEqual(multiSegments, [
  [
    [0, 0, 0, 0],
    [1, 0, 0, 1]
  ]
], 'decode multiple segments on one line');

// 6. Multiple lines separated by semicolons and empty lines
// "AAAA;;EAAA" -> line 0 has [0,0,0,0], line 1 is empty [], line 2 has [2,0,0,0]
const multiLines = decode('AAAA;;EAAA');
assert.deepStrictEqual(multiLines, [
  [[0, 0, 0, 0]],
  [],
  [[2, 0, 0, 0]]
], 'decode multiple lines with empty lines');

// 7. Structured helper verification
const structured = decodeToStructured('AAAAA,CAAC;EAAA');
assert.strictEqual(structured.length, 2, 'structured representation has 2 lines');
assert.deepStrictEqual(structured[0][0], {
  generatedColumn: 0,
  sourceIndex: 0,
  originalLine: 0,
  originalColumn: 0,
  nameIndex: 0
}, 'structured segment with 5 fields');
assert.deepStrictEqual(structured[0][1], {
  generatedColumn: 1,
  sourceIndex: 0,
  originalLine: 0,
  originalColumn: 1
}, 'structured segment with 4 fields');
assert.deepStrictEqual(structured[1][0], {
  generatedColumn: 2,
  sourceIndex: 0,
  originalLine: 0,
  originalColumn: 1
}, 'structured segment on second line');

// 8. Count segments helper verification
assert.strictEqual(countSegments('AAAAA,CAAC;EAAA'), 3, 'countSegments correctly counts 3 segments');

console.log('Contract tests passed successfully.');