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 diff.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:
  - diff.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:sha256:4e3f811c09fd72678e4e8c8d290de0c3984f4637a4f75b8139511789325e1403","contract":["applyPatch(source, uniDiffString) applies a unified diff string to source and returns the patched string","applyPatch(source, parsedPatch) accepts a structured patch object or a 1-element array from parsePatch","applyPatch returns false when hunk context does not match within options.fuzzFactor (default 0)","applyPatch(source, patch, { fuzzFactor }) tolerates up to fuzzFactor mismatched context lines","applyPatch(source, patch, { compareLine }) uses the custom comparator for context and removal checks","applyPatch throws Error('applyPatch only works with a single input.') when given an array of length \u003e 1"],"goal":"verify diff.applyPatch in pkg:npm/diff@5.2.2","kind":"HOW","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"symbols":["diff.applyPatch"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/diff@5.2.2"],"schemaVersion":1,"subject":"pkg:npm/diff@5.2.2","symbols":["diff.applyPatch"],"verifierAdapter":"node-typescript@1"}

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

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

import assert from "node:assert/strict";
import { applyPatch, createPatch, parsePatch, structuredPatch } from "diff";

// 1. Apply a unified diff string to source text
const source = "line1\nline2\nline3\n";
const target = "line1\nline2-modified\nline3\nline4\n";
const patchStr = createPatch("file.txt", source, target);
const patchedFromStr = applyPatch(source, patchStr);
assert.equal(patchedFromStr, target);

// 2. Apply a structured patch object or single-element array from parsePatch
const parsedArray = parsePatch(patchStr);
assert.equal(applyPatch(source, parsedArray), target);
const structured = structuredPatch("file.txt", "file.txt", source, target);
assert.equal(applyPatch(source, structured), target);

// 3. Returns false when patch context does not fit within fuzzFactor (default 0)
const mismatchedSource = "other1\nother2\nother3\n";
assert.equal(applyPatch(mismatchedSource, patchStr), false);

// 4. Applies patch with fuzzFactor when context lines partially differ
const slightlyShiftedSource = "line1-changed-context\nline2\nline3\n";
assert.equal(applyPatch(slightlyShiftedSource, patchStr), false);
const patchedWithFuzz = applyPatch(slightlyShiftedSource, patchStr, { fuzzFactor: 1 });
assert.equal(patchedWithFuzz, "line1-changed-context\nline2-modified\nline3\nline4\n");

// 5. Custom compareLine option overrides strict line equality check
const caseVariantSource = "LINE1\nline2\nLINE3\n";
const patchedWithCompare = applyPatch(caseVariantSource, patchStr, {
  compareLine(lineNumber, line, operation, patchContent) {
    return line.toLowerCase() === patchContent.toLowerCase();
  }
});
assert.equal(patchedWithCompare, "LINE1\nline2-modified\nLINE3\nline4\n");

// 6. Throws Error when passed a multi-file patch array with more than 1 element
assert.throws(
  () => applyPatch(source, [structured, structured]),
  { message: "applyPatch only works with a single input." }
);