diff 5.2.2: applyPatch

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 applyPatch in pkg:npm/diff@5.2.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/diff@5.2.2
Demonstrate these symbols/APIs:
  - applyPatch

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:c952e5eb92ed30bfba608b1f008d477336b832c3741f55e377012a2ffcd6c7ae","contract":["applyPatch applies a unified diff string, a parsed patch object, or a single-element parsed patch array to reproduce the patched text","applyPatch returns false when hunk context does not match within fuzzFactor and succeeds when fuzzFactor or custom compareLine permits the mismatch","applyPatch throws Error('applyPatch only works with a single input.') when given an array of more than one parsed patch"],"goal":"verify applyPatch in pkg:npm/diff@5.2.2","kind":"HOW","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"symbols":["applyPatch"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","runtime":"node","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"subject":"pkg:npm/diff@5.2.2","symbols":["applyPatch"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-diff-applypatch",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-diff-applypatch",
      "version": "1.0.0",
      "dependencies": {
        "diff": "5.2.2"
      }
    },
    "node_modules/diff": {
      "version": "5.2.2",
      "resolved": "https://registry.npmjs.org/diff/-/diff-5.2.2.tgz",
      "integrity": "sha512-vtcDfH3TOjP8UekytvnHH1o1P4FcUdt4eQ1Y+Abap1tk/OB2MWQvcwS2ClCd1zuIhc3JKOx6p3kod8Vfys3E+A==",
      "license": "BSD-3-Clause",
      "engines": {
        "node": ">=0.3.1"
      }
    }
  }
}

{
  "name": "sample-diff-applypatch",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "diff": "5.2.2"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify applyPatch in pkg:npm/diff@5.2.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/diff@5.2.2"
  ],
  "symbols": [
    "applyPatch"
  ]
}

import { applyPatch, createTwoFilesPatch, parsePatch } from 'diff';

export function applyUnifiedPatch(source, oldText, newText, options = {}) {
  const patchString = createTwoFilesPatch('old.txt', 'new.txt', oldText, newText, '', '');
  return applyPatch(source, patchString, options);
}

export function applyParsedPatch(source, patchString, options = {}) {
  const parsed = parsePatch(patchString);
  return applyPatch(source, parsed[0], options);
}

export function applyPatchRaw(source, uniDiff, options = {}) {
  return applyPatch(source, uniDiff, options);
}

import assert from 'node:assert/strict';
import { createTwoFilesPatch, parsePatch } from 'diff';
import { applyUnifiedPatch, applyParsedPatch, applyPatchRaw } from '../src/index.mjs';

// 1. Apply unified diff string or parsed patch object directly
const oldText = 'line1\nline2\nline3\nline4\n';
const newText = 'line1\nline2-updated\nline3\nline4\n';
const patchString = createTwoFilesPatch('old.txt', 'new.txt', oldText, newText, '', '');

assert.equal(applyUnifiedPatch(oldText, oldText, newText), newText);
assert.equal(applyParsedPatch(oldText, patchString), newText);
assert.equal(applyPatchRaw(oldText, parsePatch(patchString)), newText);

// 2. Returns false when context does not match and fuzzFactor is 0
const mismatchedSource = 'line1\ndifferent-line2\nline3\nline4\n';
assert.equal(applyPatchRaw(mismatchedSource, patchString), false);

// 3. Supports fuzzFactor and custom compareLine option
const driftedSource = 'line1-drifted\nline2\nline3\nline4\n';
assert.equal(applyPatchRaw(driftedSource, patchString, { fuzzFactor: 0 }), false);
assert.equal(
  applyPatchRaw(driftedSource, patchString, { fuzzFactor: 1 }),
  'line1-drifted\nline2-updated\nline3\nline4\n'
);

const whitespaceSource = 'line1  \nline2\nline3\nline4\n';
assert.equal(
  applyPatchRaw(whitespaceSource, patchString, {
    compareLine: (_lineNumber, line, _operation, patchContent) => line.trim() === patchContent.trim()
  }),
  'line1  \nline2-updated\nline3\nline4\n'
);

// 4. Throws Error when given an array with more than one parsed patch
const multiPatch = parsePatch(patchString + '\n' + patchString);
assert.throws(
  () => applyPatchRaw(oldText, multiPatch),
  /applyPatch only works with a single input\./
);