acorn 8.18.0: parseExpressionAt

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 acorn.parseExpressionAt in pkg:npm/acorn@8.18.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/acorn@8.18.0
Demonstrate these symbols/APIs:
  - acorn.parseExpressionAt

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:sha256:2454e3b22563855d5dbe8f805a449826580cfcb69ad5d80c0f363f44f5ecdea8","contract":["acorn.parseExpressionAt(input, offset, options) parses a single JavaScript expression starting at the given offset and returns an AST Node","acorn.parseExpressionAt returns node with correct type, start, end, and expression-specific fields","acorn.parseExpressionAt supports locations and ranges options for source mapping","acorn.parseExpressionAt supports ecmaVersion option for modern ECMAScript syntax features","acorn.parseExpressionAt throws SyntaxError when given invalid JavaScript syntax at the offset"],"goal":"verify acorn.parseExpressionAt in pkg:npm/acorn@8.18.0","kind":"HOW","packages":["pkg:npm/acorn@8.18.0"],"schemaVersion":1,"symbols":["acorn.parseExpressionAt"]},"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/acorn@8.18.0"],"schemaVersion":1,"subject":"pkg:npm/acorn@8.18.0","symbols":["acorn.parseExpressionAt"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-acorn-parse-expression-at",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-acorn-parse-expression-at",
      "version": "1.0.0",
      "dependencies": {
        "acorn": "8.18.0"
      }
    },
    "node_modules/acorn": {
      "version": "8.18.0",
      "resolved": "https://registry.npmjs.org/acorn/-/acorn-8.18.0.tgz",
      "integrity": "sha512-lGq+9yr1/GuAWaVYIHRjvvySG5/4VfKIvC8EWxStPdcDh/Ka7FG3twP6v4d5BkravUilhIAsG4Qj83t02LWUPQ==",
      "license": "MIT",
      "bin": {
        "acorn": "bin/acorn"
      },
      "engines": {
        "node": ">=0.4.0"
      }
    }
  }
}

{
  "name": "sample-acorn-parse-expression-at",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "acorn": "8.18.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify acorn.parseExpressionAt in pkg:npm/acorn@8.18.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/acorn@8.18.0"
  ],
  "symbols": [
    "acorn.parseExpressionAt"
  ]
}

import assert from 'node:assert/strict';
import * as acorn from 'acorn';

// 1. Basic expression parsing at offset 0
{
  const code = '1 + 2';
  const node = acorn.parseExpressionAt(code, 0, { ecmaVersion: 2020 });
  assert.equal(node.type, 'BinaryExpression');
  assert.equal(node.start, 0);
  assert.equal(node.end, 5);
  assert.equal(node.operator, '+');
  assert.equal(node.left.type, 'Literal');
  assert.equal(node.left.value, 1);
  assert.equal(node.right.type, 'Literal');
  assert.equal(node.right.value, 2);
}

// 2. Parsing expression starting at arbitrary offset
{
  const code = 'const msg = "hello " + name;';
  const offset = 12; // Start of `"hello " + name`
  const node = acorn.parseExpressionAt(code, offset, { ecmaVersion: 2020 });
  assert.equal(node.type, 'BinaryExpression');
  assert.equal(node.start, 12);
  assert.equal(node.end, 27);
  assert.equal(node.left.type, 'Literal');
  assert.equal(node.left.value, 'hello ');
  assert.equal(node.right.type, 'Identifier');
  assert.equal(node.right.name, 'name');
}

// 3. Options: locations and ranges
{
  const code = 'foo.bar(42)';
  const node = acorn.parseExpressionAt(code, 0, {
    ecmaVersion: 2020,
    locations: true,
    ranges: true
  });
  assert.equal(node.type, 'CallExpression');
  assert.deepEqual(node.range, [0, 11]);
  assert.ok(node.loc);
  assert.equal(node.loc.start.line, 1);
  assert.equal(node.loc.start.column, 0);
  assert.equal(node.loc.end.line, 1);
  assert.equal(node.loc.end.column, 11);
}

// 4. Modern syntax with optional chaining and nullish coalescing
{
  const code = 'user?.profile?.name ?? "Anonymous"';
  const node = acorn.parseExpressionAt(code, 0, { ecmaVersion: 2022 });
  assert.equal(node.type, 'LogicalExpression');
  assert.equal(node.operator, '??');
  assert.equal(node.left.type, 'ChainExpression');
  assert.equal(node.right.value, 'Anonymous');
}

// 5. Syntax error handling
{
  assert.throws(
    () => {
      acorn.parseExpressionAt('1 +', 0, { ecmaVersion: 2020 });
    },
    (err) => {
      assert.ok(err instanceof SyntaxError);
      assert.ok(typeof err.pos === 'number');
      return true;
    }
  );
}

console.log('All contract assertions passed successfully.');