@babel/types 7.29.8: assertBlockStatement

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 @babel/types.assertBlockStatement in pkg:npm/%40babel/types@7.29.8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40babel/types@7.29.8
Demonstrate these symbols/APIs:
  - @babel/types.assertBlockStatement
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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.

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      "name": "sample-babel-types-assert-block-statement",
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      "engines": {
        "node": ">=6.9.0"
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{
  "name": "sample-babel-types-assert-block-statement",
  "version": "1.0.0",
  "private": true,
  "main": "src/index.js",
  "dependencies": {
    "@babel/types": "7.29.8"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify @babel/types.assertBlockStatement in pkg:npm/%40babel/types@7.29.8",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40babel/types@7.29.8"
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}

const t = require("@babel/types");

/**
 * Validates that an AST node is a valid BlockStatement.
 * Uses @babel/types.assertBlockStatement to enforce type integrity.
 *
 * @param {object} node - The AST node to validate.
 * @param {object} [opts] - Optional properties to match against the node.
 * @returns {object} The validated BlockStatement node.
 */
function validateBlockStatement(node, opts) {
  t.assertBlockStatement(node, opts);
  return node;
}

/**
 * Creates a BlockStatement containing the given statement nodes and validates it.
 *
 * @param {Array<object>} statements - Array of Statement AST nodes.
 * @param {Array<object>} [directives] - Optional array of Directive AST nodes.
 * @returns {object} The created and asserted BlockStatement node.
 */
function createVerifiedBlockStatement(statements, directives) {
  const block = t.blockStatement(statements, directives);
  t.assertBlockStatement(block);
  return block;
}

/**
 * Extracts and validates the body block of a function or control structure.
 * Supports function declarations (node.body) and if statements (node.consequent).
 *
 * @param {object} containerNode - An AST node containing a body BlockStatement.
 * @returns {object} The validated body BlockStatement node.
 */
function extractVerifiedBody(containerNode) {
  if (!containerNode) {
    throw new Error("Container node must be provided");
  }
  const body = containerNode.body || containerNode.consequent;
  if (!body) {
    throw new Error("Container node must have a body or consequent property");
  }
  t.assertBlockStatement(body);
  return body;
}

module.exports = {
  validateBlockStatement,
  createVerifiedBlockStatement,
  extractVerifiedBody,
};

const assert = require("assert");
const t = require("@babel/types");
const {
  validateBlockStatement,
  createVerifiedBlockStatement,
  extractVerifiedBody,
} = require("../src/index.js");

// Test 1: assertBlockStatement succeeds without throwing when passed a valid BlockStatement node
{
  const emptyBlock = t.blockStatement([]);
  assert.doesNotThrow(() => {
    t.assertBlockStatement(emptyBlock);
  });
  const result = validateBlockStatement(emptyBlock);
  assert.strictEqual(result, emptyBlock);
}

// Test 2: assertBlockStatement succeeds when passed a BlockStatement containing multiple statement nodes
{
  const stmt1 = t.expressionStatement(t.identifier("a"));
  const stmt2 = t.returnStatement(t.numericLiteral(42));
  const block = createVerifiedBlockStatement([stmt1, stmt2]);
  assert.strictEqual(block.type, "BlockStatement");
  assert.strictEqual(block.body.length, 2);
  assert.doesNotThrow(() => {
    t.assertBlockStatement(block);
  });
}

// Test 3: assertBlockStatement throws an Error when passed a non-BlockStatement AST node
{
  const ident = t.identifier("x");
  assert.throws(
    () => {
      t.assertBlockStatement(ident);
    },
    (err) => {
      return err instanceof Error && /Expected type "BlockStatement"/.test(err.message);
    }
  );

  const numLit = t.numericLiteral(123);
  assert.throws(
    () => {
      validateBlockStatement(numLit);
    },
    (err) => {
      return err instanceof Error && /Expected type "BlockStatement"/.test(err.message);
    }
  );
}

// Test 4: assertBlockStatement throws an Error when passed non-node values such as primitive types or null
{
  assert.throws(() => {
    t.assertBlockStatement(null);
  }, Error);

  assert.throws(() => {
    t.assertBlockStatement(undefined);
  }, Error);

  assert.throws(() => {
    t.assertBlockStatement("not a node");
  }, Error);

  assert.throws(() => {
    t.assertBlockStatement(123);
  }, Error);

  assert.throws(() => {
    t.assertBlockStatement({ type: "UnknownType" });
  }, (err) => {
    return err instanceof Error && /Expected type "BlockStatement"/.test(err.message);
  });
}

// Test 5: assertBlockStatement validates BlockStatement nodes within control flow and function constructs
{
  const fnBody = t.blockStatement([t.returnStatement(t.stringLiteral("hello"))]);
  const fnDecl = t.functionDeclaration(
    t.identifier("greet"),
    [],
    fnBody
  );
  const extractedFnBody = extractVerifiedBody(fnDecl);
  assert.strictEqual(extractedFnBody, fnBody);
  assert.doesNotThrow(() => {
    t.assertBlockStatement(fnDecl.body);
  });

  const ifBody = t.blockStatement([t.expressionStatement(t.identifier("doSomething"))]);
  const ifStmt = t.ifStatement(t.booleanLiteral(true), ifBody);
  const extractedIfBody = extractVerifiedBody(ifStmt);
  assert.strictEqual(extractedIfBody, ifBody);
  assert.doesNotThrow(() => {
    t.assertBlockStatement(ifStmt.consequent);
  });
}

// Test 6: assertBlockStatement supports optional property matching to verify specific node attributes
{
  const block = t.blockStatement([]);
  assert.doesNotThrow(() => {
    t.assertBlockStatement(block, { type: "BlockStatement" });
  });

  assert.throws(
    () => {
      t.assertBlockStatement(block, { type: "ExpressionStatement" });
    },
    (err) => {
      return err instanceof Error && /Expected type "BlockStatement" with option/.test(err.message);
    }
  );
}

console.log("All @babel/types.assertBlockStatement contract tests passed.");