diff 5.2.2: parsePatch

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 parsePatch 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:
  - parsePatch

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:sha256:495946816b5b399adf3f6efac74690d933bf04a6ec1d53039547765c44330c71","contract":["parsePatch parses unified diff strings into structured patch descriptors with oldFileName, newFileName, oldHeader, newHeader, and hunks containing oldStart, oldLines, newStart, newLines, and prefixed lines","parsePatch splits multi-file unified diffs with Index headers and multiple @@ hunk headers into separate file descriptors and ordered hunk arrays that applyPatch consumes directly","parsePatch preserves '\\ No newline at end of file' markers in hunk lines and throws on unknown line prefixes or mismatched hunk line counts when { strict: true } is passed"],"goal":"verify parsePatch in pkg:npm/diff@5.2.2","kind":"HOW","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"symbols":["parsePatch"]},"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":["parsePatch"],"verifierAdapter":"node-typescript@1"}

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

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

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

export function parseUnifiedDiff(patchText, options) {
  return parsePatch(patchText, options);
}

export function createParseAndApply(oldFile, newFile, oldText, newText, oldHeader = '', newHeader = '') {
  const rawPatch = createTwoFilesPatch(oldFile, newFile, oldText, newText, oldHeader, newHeader);
  const parsed = parsePatch(rawPatch);
  const applied = applyPatch(oldText, parsed[0]);
  return { rawPatch, parsed, applied };
}

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

// 1. Parse a single-file unified diff with headers, hunk range, and line prefixes
const { rawPatch, parsed, applied } = createParseAndApply(
  'a/config.txt',
  'b/config.txt',
  'host=localhost\nport=8080\ndebug=false\n',
  'host=localhost\nport=9090\ndebug=true\n',
  'rev1',
  'rev2'
);

assert.equal(parsed.length, 1);
assert.equal(parsed[0].oldFileName, 'a/config.txt');
assert.equal(parsed[0].newFileName, 'b/config.txt');
assert.equal(parsed[0].oldHeader, 'rev1');
assert.equal(parsed[0].newHeader, 'rev2');
assert.equal(parsed[0].hunks.length, 1);

const hunk = parsed[0].hunks[0];
assert.equal(hunk.oldStart, 1);
assert.equal(hunk.oldLines, 3);
assert.equal(hunk.newStart, 1);
assert.equal(hunk.newLines, 3);
assert.deepEqual(hunk.lines, [
  ' host=localhost',
  '-port=8080',
  '-debug=false',
  '+port=9090',
  '+debug=true'
]);
assert.equal(applied, 'host=localhost\nport=9090\ndebug=true\n');

// 2. Parse a multi-file diff containing multiple hunks and index headers
const multiFilePatch = [
  'Index: first.txt',
  '===================================================================',
  '--- a/first.txt\told',
  '+++ b/first.txt\tnew',
  '@@ -1,2 +1,2 @@',
  ' alpha',
  '-beta',
  '+BETA',
  '@@ -10,2 +10,3 @@',
  ' omega',
  '+extra',
  ' end',
  'Index: second.txt',
  '===================================================================',
  '--- a/second.txt',
  '+++ b/second.txt',
  '@@ -1,1 +1,1 @@',
  '-hello',
  '+world',
  ''
].join('\n');

const multiParsed = parseUnifiedDiff(multiFilePatch);
assert.equal(multiParsed.length, 2);
assert.equal(multiParsed[0].index, 'first.txt');
assert.equal(multiParsed[0].oldFileName, 'a/first.txt');
assert.equal(multiParsed[0].newFileName, 'b/first.txt');
assert.equal(multiParsed[0].hunks.length, 2);
assert.equal(multiParsed[0].hunks[0].oldStart, 1);
assert.equal(multiParsed[0].hunks[1].oldStart, 10);
assert.equal(multiParsed[0].hunks[1].newLines, 3);

assert.equal(multiParsed[1].index, 'second.txt');
assert.equal(multiParsed[1].oldFileName, 'a/second.txt');
assert.equal(multiParsed[1].newFileName, 'b/second.txt');
assert.equal(multiParsed[1].hunks.length, 1);
assert.deepEqual(multiParsed[1].hunks[0].lines, ['-hello', '+world']);

// 3. Parse no-newline-at-end-of-file markers and reject malformed hunk lines in strict mode
const noNewlinePatch = [
  '--- a/eof.txt',
  '+++ b/eof.txt',
  '@@ -1,1 +1,1 @@',
  '-old-no-eol',
  '\\ No newline at end of file',
  '+new-no-eol',
  '\\ No newline at end of file',
  ''
].join('\n');

const eofParsed = parseUnifiedDiff(noNewlinePatch);
assert.equal(eofParsed.length, 1);
assert.equal(eofParsed[0].hunks[0].lines.includes('\\ No newline at end of file'), true);

const countMismatchPatch = [
  '--- a/bad.txt',
  '+++ b/bad.txt',
  '@@ -1,2 +1,2 @@',
  ' valid-context',
  ''
].join('\n');

assert.throws(
  () => parseUnifiedDiff(countMismatchPatch, { strict: true }),
  /Added line count did not match for hunk at line 3/
);

const unknownLinePatch = [
  '--- a/bad.txt',
  '+++ b/bad.txt',
  '@@ -1,1 +1,1 @@',
  '-old',
  '+new',
  'INVALID_PREFIX_LINE',
  ''
].join('\n');

assert.throws(
  () => parseUnifiedDiff(unknownLinePatch, { strict: true }),
  /Unknown line/
);