diff 5.2.2: createTwoFilesPatch

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 createTwoFilesPatch 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:
  - createTwoFilesPatch

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:aa33cf3527cb5fc2db29634df5e2e16209afe0ee001be7128126f1e1b8e12e9f","contract":["createTwoFilesPatch formats a unified diff between oldFileName and newFileName with optional tab-separated oldHeader and newHeader lines that applyPatch applies to reproduce newStr","createTwoFilesPatch prepends an 'Index: \u003cfileName\u003e' line only when oldFileName equals newFileName and omits header tabs when oldHeader or newHeader are undefined","createTwoFilesPatch forwards options.context (default 4) to control surrounding context lines and hunk splitting, and emits '\\ No newline at end of file' when inputs lack a trailing newline"],"goal":"verify createTwoFilesPatch in pkg:npm/diff@5.2.2","kind":"HOW","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"symbols":["createTwoFilesPatch"]},"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":["createTwoFilesPatch"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-diff-create-two-files-patch",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-diff-create-two-files-patch",
      "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-create-two-files-patch",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "diff": "5.2.2"
  }
}

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

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

export function generateTwoFilesDiff(
  oldFileName,
  newFileName,
  oldStr,
  newStr,
  oldHeader,
  newHeader,
  options
) {
  return createTwoFilesPatch(
    oldFileName,
    newFileName,
    oldStr,
    newStr,
    oldHeader,
    newHeader,
    options
  );
}

export function roundTripTwoFilesPatch(
  oldFileName,
  newFileName,
  oldStr,
  newStr,
  oldHeader,
  newHeader,
  options
) {
  const patch = createTwoFilesPatch(
    oldFileName,
    newFileName,
    oldStr,
    newStr,
    oldHeader,
    newHeader,
    options
  );
  const parsed = parsePatch(patch);
  const applied = applyPatch(oldStr, patch);
  return { patch, parsed, applied };
}

import assert from 'node:assert/strict';
import { generateTwoFilesDiff, roundTripTwoFilesPatch } from '../src/index.mjs';

// 1. Distinct file names with headers and unified diff application
const oldContent = 'line1\nline2\nline3\nline4\nline5\n';
const newContent = 'line1\nline2-updated\nline3\nline4\nline5\n';
const { patch, parsed, applied } = roundTripTwoFilesPatch(
  'old/file.txt',
  'new/file.txt',
  oldContent,
  newContent,
  'rev1',
  'rev2'
);

assert.equal(patch.startsWith('===================================================================\n'), true);
assert.equal(patch.includes('Index: '), false);
assert.equal(patch.includes('--- old/file.txt\trev1\n'), true);
assert.equal(patch.includes('+++ new/file.txt\trev2\n'), true);
assert.equal(parsed.length, 1);
assert.equal(parsed[0].oldFileName, 'old/file.txt');
assert.equal(parsed[0].newFileName, 'new/file.txt');
assert.equal(parsed[0].oldHeader, 'rev1');
assert.equal(parsed[0].newHeader, 'rev2');
assert.equal(applied, newContent);

// 2. Identical file names prepend Index header and omit undefined headers
const sameFilePatch = generateTwoFilesDiff(
  'same.txt',
  'same.txt',
  'alpha\nbeta\n',
  'alpha\ngamma\n'
);
assert.equal(sameFilePatch.startsWith('Index: same.txt\n===================================================================\n'), true);
assert.equal(sameFilePatch.includes('--- same.txt\n+++ same.txt\n'), true);

// 3. Context option splits distant changes into separate hunks
const manyLinesOld = '1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n';
const manyLinesNew = '1-mod\n2\n3\n4\n5\n6\n7\n8\n9\n10-mod\n';
const defaultContext = roundTripTwoFilesPatch('a.txt', 'b.txt', manyLinesOld, manyLinesNew);
const narrowContext = roundTripTwoFilesPatch(
  'a.txt',
  'b.txt',
  manyLinesOld,
  manyLinesNew,
  undefined,
  undefined,
  { context: 1 }
);
assert.equal(defaultContext.parsed[0].hunks.length, 1);
assert.equal(narrowContext.parsed[0].hunks.length, 2);
assert.equal(narrowContext.applied, manyLinesNew);

// 4. Missing trailing newline emits "\ No newline at end of file" marker
const noEolPatch = generateTwoFilesDiff('a.txt', 'b.txt', 'hello', 'world');
assert.equal(noEolPatch.includes('\\ No newline at end of file'), true);