typescript 5.9.3: Fix ts.createProgram becoming undefined after upgrading to typescript 7

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{
  "name": "csx-sample-typescript-compile-api",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "typescript": "5.9.3",
    "typescript7": "npm:typescript@7.0.2"
  }
}

import { createRequire } from 'node:module';

const require = createRequire(import.meta.url);

// TypeScript 7 is the native port, and its npm package no longer ships the
// JavaScript compiler API: `typescript@7` exposes only `version` and
// `versionMajorMinor`, from BOTH the ESM and CommonJS entry points. Every
// tool built on ts.createProgram, ts.transpileModule or ts.createSourceFile
// stops working the moment the dependency resolves to 7 — and it fails as
// "Cannot read properties of undefined", not as a missing module, because
// the package is still there.
//
// The API also has no ESM named exports on 5.x: `import ts from
// 'typescript'` gives the namespace as a default export, and destructuring
// named bindings from it is what breaks under bundlers.
export function loadCompiler(specifier = 'typescript') {
  return require(specifier);
}

export function hasCompilerAPI(ts) {
  return typeof ts.createProgram === 'function' &&
    typeof ts.createSourceFile === 'function' &&
    ts.ScriptTarget !== undefined;
}

// Type-check a source string without touching disk.
//
// The CompilerHost is the whole trick, and hand-rolling one is where this
// usually goes wrong. The default library is not a single file: lib.*.d.ts
// pulls in more lib files through /// <reference lib="..." /> directives,
// so a host that serves only the one file it was told about type checks
// against no global types and reports TS2318 "Cannot find global type
// 'Array'" — which reads like a bug in the checked code rather than in the
// host. Delegating to ts.createCompilerHost and intercepting ONLY the
// in-memory file keeps that resolution intact.
export function check(source, options = {}) {
  const ts = loadCompiler('typescript');
  const fileName = 'input.ts';
  const opts = { strict: true, noEmit: true, target: ts.ScriptTarget.ES2022, ...options };

  const inMemory = ts.createSourceFile(fileName, source, opts.target, true);
  const base = ts.createCompilerHost(opts, true);
  const host = {
    ...base,
    getSourceFile: (name, languageVersion, onError) =>
      (name === fileName ? inMemory : base.getSourceFile(name, languageVersion, onError)),
    fileExists: (name) => name === fileName || base.fileExists(name),
    readFile: (name) => (name === fileName ? source : base.readFile(name)),
    writeFile: () => {},
  };

  const program = ts.createProgram([fileName], opts, host);
  return ts.getPreEmitDiagnostics(program).map((diag) => ({
    code: diag.code,
    message: ts.flattenDiagnosticMessageText(diag.messageText, ' '),
  }));
}

import { strict as assert } from 'node:assert';
import { check, loadCompiler, hasCompilerAPI } from '../src/index.mjs';

// 1. The migration fact, proven rather than claimed: both majors are
//    installed, and only 5.x carries the compiler API.
const ts5 = loadCompiler('typescript');
const ts7 = loadCompiler('typescript7');
assert.match(ts5.version, /^5\./);
assert.match(ts7.version, /^7\./);
assert.equal(hasCompilerAPI(ts5), true, 'typescript 5 exposes the compiler API');
assert.equal(hasCompilerAPI(ts7), false, 'typescript 7 does not');
assert.equal(typeof ts7.createProgram, 'undefined');
assert.deepEqual(Object.keys(ts7).sort(), ['version', 'versionMajorMinor']);

// 2. With 5.x the in-memory type check works.
const bad = check('const n: number = "not a number";');
assert.ok(bad.length > 0, 'a type error must be reported');
assert.ok(bad.some((d) => d.code === 2322), // Type 'X' is not assignable to type 'Y'
  'the assignment error must be reported: ' + JSON.stringify(bad));
assert.match(bad.find((d) => d.code === 2322).message, /not assignable/);

assert.deepEqual(check('const n: number = 42; export {};'), []);

// 3. strict is not cosmetic: it decides whether this compiles at all.
const implicitAny = 'function f(x) { return x; } export {};';
assert.ok(check(implicitAny, { strict: true }).some((d) => d.code === 7006),
  'implicit any should be an error under strict');
assert.deepEqual(check(implicitAny, { strict: false }), []);

console.log('CONTRACT PASS: the compiler API works on 5.x and is absent from 7.x');