test: guard ES5 runtime APIs and type-check consumers in CI

Follow-up to the ES5 syntax fix, closing the gaps that investigation left.

An ES5-only runtime sandbox. The acorn check catches syntax, but syntax is
only half the contract: preset-env lowers syntax and never polyfills library
calls, so one `Array.prototype.includes` in the parser source compiles
cleanly, passes every test on modern Node, and throws on the browsers es5.js
exists for. The new test runs both legacy bundles in a vm context with the
post-ES5.1 globals, statics and prototype methods deleted, and asserts
bundled.js additionally installs the polyfills its README entry promises.
Includes a test that the sandbox really strips, so it cannot quietly pass
against a modern global.

A consumer type-check across every module resolution mode, run in CI against
the packed tarball. attw already checks that types *resolve* per condition;
it compiles nothing, so it cannot catch a declaration that resolves correctly
and then misdescribes the runtime. Negative cases are asserted too — the maps
must stay non-importable as named exports, which is the line index.d.mts
draws deliberately and only a failing compile can hold.

Also documents two findings that were investigated and deliberately left
alone: the bundled.js size increase is the core-js 2 -> 3 upgrade rather than
waste, and `useBuiltIns: 'usage'` would shrink it by breaking the documented
"all needed polyfills" contract; and the src/*.js ESM-in-CJS wart (publint
warnings, Yarn PnP, Node < 20.19) is longstanding and identical on 2.14.1,
with the nested-package.json fix blocked on @babel/register.

Verified by breaking each guard in turn: an ES6 API call injected into es5.js
fails the sandbox test, and an index.d.mts with its `parse` export removed
fails all three ESM resolution modes while the CJS modes correctly still pass.

.github/workflows/pull-request.yml

@@ -128,3 +128,13 @@ jobs:
       # of bowser, and preserved here on purpose.
       - name: Are the types wrong?
         run: pnpm exec attw --pack . --profile node16 --entrypoints .
+
+      # attw checks that the types *resolve* to the right file per condition.
+      # This compiles a real consumer against the packed tarball in every
+      # module resolution mode, which is what catches a declaration that
+      # resolves fine but does not match the runtime.
+      - name: Type-check consumers
+        run: |
+          mkdir -p tarball
+          npm pack --pack-destination ./tarball
+          node test/types/check.mjs tarball/*.tgz

package.json

@@ -118,7 +118,8 @@
     ],
     "files": [
       "test/**/*.js",
-      "!test/package/**"
+      "!test/package/**",
+      "!test/types/**"
     ]
   },
   "bugs": {
@@ -138,7 +139,8 @@
     "test:watch": "ava --watch",
     "test:package": "node test/package/smoke.cjs",
     "coverage": "nyc report --reporter=text-lcov | coveralls",
-    "generate-docs": "jsdoc -c jsdoc.json"
+    "generate-docs": "jsdoc -c jsdoc.json",
+    "test:types": "node test/types/check.mjs"
   },
   "license": "MIT",
   "packageManager": "pnpm@11.18.0"

test/acceptance/test-es5-runtime.js

@@ -0,0 +1,88 @@
+import test from 'ava';
+import fs from 'fs';
+import path from 'path';
+import vm from 'vm';
+
+/**
+ * Runs the legacy bundles on a global object stripped back to ES5.1.
+ *
+ * `test-es5-conformance.js` checks *syntax*. This checks *runtime APIs*, which
+ * is a separate failure mode babel cannot protect against: `@babel/preset-env`
+ * lowers syntax, but without `useBuiltIns` it never polyfills library calls. A
+ * single `Array.prototype.includes` or `Object.assign` in the parser source
+ * compiles cleanly, passes every test on modern Node, and then throws
+ * `TypeError: undefined is not a function` on the old browsers `es5.js` targets.
+ *
+ * `es5.js` ships with no polyfills at all, so it has to survive here on its own.
+ * `bundled.js` carries core-js and has to install what it needs and still work.
+ *
+ * These are build outputs — run `pnpm build` before `pnpm test`.
+ */
+const root = path.join(__dirname, '..', '..');
+
+const UA = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 '
+  + '(KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
+
+// Everything below postdates ES5.1. Not exhaustive — it covers the APIs a UA
+// parser plausibly reaches for, which is what makes it a useful tripwire.
+const ES6_GLOBALS = ['Promise', 'Symbol', 'Map', 'Set', 'WeakMap', 'WeakSet', 'Proxy', 'Reflect', 'globalThis', 'BigInt'];
+const ES6_STATICS = {
+  Object: ['assign', 'entries', 'values', 'fromEntries', 'getOwnPropertySymbols', 'setPrototypeOf'],
+  Array: ['from', 'of'],
+  String: ['raw', 'fromCodePoint'],
+  Number: ['isInteger', 'isNaN', 'parseFloat', 'isFinite', 'EPSILON'],
+  Math: ['trunc', 'sign', 'log2', 'clz32'],
+};
+const ES6_PROTOS = {
+  Array: ['includes', 'find', 'findIndex', 'flat', 'flatMap', 'fill', 'copyWithin', 'at'],
+  String: ['includes', 'startsWith', 'endsWith', 'repeat', 'padStart', 'padEnd', 'trimStart', 'trimEnd', 'matchAll', 'at', 'normalize', 'codePointAt'],
+};
+
+function createEs5Context() {
+  const context = vm.createContext({});
+  // UMD bundles look for a global; `self` is the browser-shaped one.
+  vm.runInContext('this.self = this;', context);
+  const deletions = []
+    .concat(ES6_GLOBALS.map((g) => `this.${g}`))
+    .concat(...Object.entries(ES6_STATICS).map(([o, keys]) => keys.map((k) => `${o}.${k}`)))
+    .concat(...Object.entries(ES6_PROTOS).map(([o, keys]) => keys.map((k) => `${o}.prototype.${k}`)))
+    .map((ref) => `try { delete ${ref}; } catch (e) {}`)
+    .join('\n');
+  vm.runInContext(deletions, context);
+  return context;
+}
+
+test('the ES5 sandbox actually strips the modern APIs', (t) => {
+  // Guards the guard: if stripping silently stopped working, every assertion
+  // below would pass against a fully modern global and prove nothing.
+  const context = createEs5Context();
+  t.is(vm.runInContext('typeof Promise', context), 'undefined');
+  t.is(vm.runInContext('typeof Object.assign', context), 'undefined');
+  t.is(vm.runInContext('typeof [].includes', context), 'undefined');
+  t.is(vm.runInContext('typeof "".startsWith', context), 'undefined');
+});
+
+['es5.js', 'bundled.js'].forEach((file) => {
+  test(`${file} runs on an ES5-only global`, (t) => {
+    const context = createEs5Context();
+    const source = fs.readFileSync(path.join(root, file), 'utf8');
+
+    t.notThrows(() => vm.runInContext(source, context), `${file} threw while loading`);
+    t.is(vm.runInContext('typeof this.bowser', context), 'function');
+
+    context.__ua = UA;
+    t.is(vm.runInContext('this.bowser.parse(this.__ua).browser.name', context), 'Chrome');
+    t.is(vm.runInContext('this.bowser.parse(this.__ua).os.name', context), 'macOS');
+    t.true(vm.runInContext('this.bowser.getParser(this.__ua).satisfies({ chrome: ">100" })', context));
+  });
+});
+
+test('bundled.js installs the polyfills it promises', (t) => {
+  // The README tells consumers to reach for bundled.js when they have no
+  // polyfills of their own, so it has to actually populate the environment.
+  const context = createEs5Context();
+  vm.runInContext(fs.readFileSync(path.join(root, 'bundled.js'), 'utf8'), context);
+  t.is(vm.runInContext('typeof Promise', context), 'function');
+  t.is(vm.runInContext('typeof Object.assign', context), 'function');
+  t.is(vm.runInContext('typeof [].includes', context), 'function');
+});

test/package/assertions.cjs

@@ -77,6 +77,14 @@ check('constant maps are exposed', function () {
 
 // The src/*.js files are ES module sources, so they resolve but do not execute
 // under require(). Bundlers are the real consumer here. Assert resolution only.
+//
+// This is also why publint warns on every `pkg.exports["./src/*"]` entry, and
+// why these paths fail under Yarn PnP (ERR_REQUIRE_CYCLE_MODULE) and on Node
+// below 20.19, which has no module-syntax detection. Verified identical on
+// 2.14.1, so it is longstanding rather than new. The obvious fix — a nested
+// `src/package.json` with `"type": "module"` — would stop `@babel/register`
+// from loading `src/` and take the whole AVA suite with it, so the wart stays
+// until the test tooling moves off `require()` hooks.
 [
   'bowser.js', 'constants.js', 'parser.js', 'parser-browsers.js',
   'parser-engines.js', 'parser-os.js', 'parser-platforms.js', 'utils.js',

test/types/check.mjs

@@ -0,0 +1,135 @@
+/**
+ * Type-checks a real consumer against the *packed* package under every module
+ * resolution mode TypeScript offers.
+ *
+ *   node test/types/check.mjs <path-to-bowser-x.y.z.tgz>
+ *
+ * `attw` already runs in CI, but it answers a narrower question: whether the
+ * types *resolve* to the right file for each condition. It does not compile
+ * anything, so it cannot catch a declaration that resolves fine and then fails
+ * to describe the runtime — a missing member, a wrong signature, or a named
+ * export declared in `index.d.mts` that `bowser.mjs` does not actually have.
+ *
+ * Both directions are asserted. The negative cases matter as much as the
+ * positive ones: `index.d.mts` deliberately omits `BROWSER_MAP` and friends as
+ * named exports because importing them that way throws at runtime, and only a
+ * compile that is expected to *fail* can hold that line.
+ *
+ * Run against the tarball rather than the repo so the exports map, the
+ * `types`/`typesVersions` fields and the published file list are all exercised
+ * exactly as a consumer sees them.
+ */
+import cp from 'node:child_process';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const repoRoot = path.join(here, '..', '..');
+const tsc = path.join(repoRoot, 'node_modules', '.bin', 'tsc');
+
+const tarball = process.argv[2];
+if (!tarball || !fs.existsSync(tarball)) {
+  console.error('usage: node test/types/check.mjs <path-to-tarball.tgz>');
+  process.exit(1);
+}
+
+/** Each mode a real consumer can be configured with. */
+const MODES = [
+  { name: 'node10 (CJS)', moduleResolution: 'node10', module: 'commonjs', type: 'commonjs', fixture: 'consumer-cjs.ts' },
+  { name: 'node16 (CJS)', moduleResolution: 'node16', module: 'node16', type: 'commonjs', fixture: 'consumer-cjs.ts' },
+  { name: 'node16 (ESM)', moduleResolution: 'node16', module: 'node16', type: 'module', fixture: 'consumer-esm.ts' },
+  { name: 'nodenext (ESM)', moduleResolution: 'nodenext', module: 'nodenext', type: 'module', fixture: 'consumer-esm.ts' },
+  { name: 'bundler', moduleResolution: 'bundler', module: 'esnext', type: 'module', fixture: 'consumer-esm.ts' },
+];
+
+/**
+ * Imports that must NOT compile, because the runtime does not provide them.
+ * Keeps `index.d.mts` honest — if any of these starts compiling, the types are
+ * promising something `bowser.mjs` will not deliver.
+ */
+const MUST_NOT_COMPILE = [
+  ['BROWSER_MAP is not a named export', 'import { BROWSER_MAP } from "bowser"; export default BROWSER_MAP;'],
+  ['OS_MAP is not a named export', 'import { OS_MAP } from "bowser"; export default OS_MAP;'],
+  ['ENGINE_MAP is not a named export', 'import { ENGINE_MAP } from "bowser"; export default ENGINE_MAP;'],
+  ['PLATFORMS_MAP is not a named export', 'import { PLATFORMS_MAP } from "bowser"; export default PLATFORMS_MAP;'],
+  ['Parser is a type, not a value', 'import { Parser } from "bowser"; export default new Parser("x");'],
+];
+
+const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'bowser-types-'));
+const modules = path.join(tmp, 'node_modules');
+fs.mkdirSync(modules, { recursive: true });
+cp.execFileSync('tar', ['xzf', path.resolve(tarball), '-C', modules]);
+fs.renameSync(path.join(modules, 'package'), path.join(modules, 'bowser'));
+
+/** Runs tsc over a single file in a project configured for `mode`. */
+function typeCheck(mode, fileName, source) {
+  // Nested one level under `tmp`, so resolution walks up into tmp/node_modules
+  // the way a real consumer's does. `paths` would short-circuit the exports map.
+  const dir = path.join(tmp, `case-${Math.abs(hash(mode.name + fileName))}`);
+  fs.mkdirSync(dir, { recursive: true });
+  fs.writeFileSync(path.join(dir, 'app.ts'), source);
+  fs.writeFileSync(path.join(dir, 'package.json'), JSON.stringify({
+    name: 'consumer', version: '1.0.0', private: true, type: mode.type,
+  }));
+  fs.writeFileSync(path.join(dir, 'tsconfig.json'), JSON.stringify({
+    compilerOptions: {
+      strict: true,
+      noEmit: true,
+      // Do not skip: a broken .d.ts in the package itself must fail the check.
+      skipLibCheck: false,
+      target: 'es2020',
+      module: mode.module,
+      moduleResolution: mode.moduleResolution,
+      esModuleInterop: true,
+      resolveJsonModule: true,
+      types: [],
+    },
+    files: ['app.ts'],
+  }));
+  const result = cp.spawnSync(tsc, ['-p', 'tsconfig.json'], { cwd: dir, encoding: 'utf8' });
+  return { ok: result.status === 0, output: `${result.stdout || ''}${result.stderr || ''}`.trim() };
+}
+
+function hash(s) {
+  let h = 0;
+  for (let i = 0; i < s.length; i += 1) { h = ((h << 5) - h + s.charCodeAt(i)) | 0; }
+  return h;
+}
+
+let failures = 0;
+console.log(`Type-checking consumers against ${path.basename(tarball)}\n`);
+
+for (const mode of MODES) {
+  const source = fs.readFileSync(path.join(here, 'fixtures', mode.fixture), 'utf8');
+  const { ok, output } = typeCheck(mode, mode.fixture, source);
+  if (ok) {
+    console.log(`  ok    ${mode.name.padEnd(16)} ${mode.fixture}`);
+  } else {
+    failures += 1;
+    console.log(`  FAIL  ${mode.name.padEnd(16)} ${mode.fixture}\n${output.replace(/^/gm, '          ')}`);
+  }
+}
+
+console.log('');
+// Only needs one ESM-shaped mode; the .d.mts is what is under test.
+const negativeMode = MODES.find((m) => m.name === 'node16 (ESM)');
+for (const [label, source] of MUST_NOT_COMPILE) {
+  const { ok } = typeCheck(negativeMode, `negative-${label}`, source);
+  if (ok) {
+    failures += 1;
+    console.log(`  FAIL  types accept something the runtime rejects: ${label}`);
+  } else {
+    console.log(`  ok    rejected: ${label}`);
+  }
+}
+
+try { fs.rmSync(tmp, { recursive: true, force: true }); } catch { /* best effort */ }
+
+console.log('');
+if (failures) {
+  console.error(`${failures} type check(s) failed`);
+  process.exit(1);
+}
+console.log(`all ${MODES.length + MUST_NOT_COMPILE.length} type checks passed`);

test/types/fixtures/consumer-cjs.ts

@@ -0,0 +1,15 @@
+// A CommonJS consumer: default import via esModuleInterop, types reached
+// through the `export =` namespace. This is what `moduleResolution: node10`
+// and `node16` (from CJS) consumers write.
+import Bowser from 'bowser';
+
+const UA = 'Mozilla/5.0 (Macintosh) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
+
+const result: Bowser.Parser.ParsedResult = Bowser.parse(UA);
+const parser: Bowser.Parser.Parser = Bowser.getParser(UA);
+const name: string | undefined = result.browser.name;
+const satisfies: boolean | undefined = parser.satisfies({ chrome: '>100' });
+const hints: Bowser.ClientHints = { mobile: false };
+const maps: Record<string, string> = Bowser.BROWSER_MAP;
+
+export { name, satisfies, hints, maps };

test/types/fixtures/consumer-esm.ts

@@ -0,0 +1,17 @@
+// An ES module consumer: default plus named imports, types imported as types.
+// This is `moduleResolution: node16` (from ESM), `nodenext` and `bundler`.
+import Bowser, { parse, getParser } from 'bowser';
+import type { ParsedResult, Parser, ClientHints, checkTree } from 'bowser';
+
+const UA = 'Mozilla/5.0 (Macintosh) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
+
+const result: ParsedResult = parse(UA);
+const parser: Parser = getParser(UA);
+const tree: checkTree = { chrome: '>100' };
+const satisfies: boolean | undefined = parser.satisfies(tree);
+const hints: ClientHints = { mobile: false };
+// BROWSER_MAP is deliberately not a named export of bowser.mjs — it only
+// exists as a static on the class. Reaching it any other way must not compile.
+const maps: Record<string, string> = Bowser.BROWSER_MAP;
+
+export { result, satisfies, hints, maps };

tsdown.config.ts

@@ -23,6 +23,17 @@ const legacyTargets = {
 /**
  * `useBuiltIns: false` for `es5.js` (syntax transpilation only) and `'entry'`
  * for `bundled.js`, which expands the `core-js/stable` import in its entry.
+ *
+ * `'entry'` is why `bundled.js` grew from 124 kB to 174 kB when it stopped
+ * being built from the deprecated `@babel/polyfill`. That package was core-js
+ * **2**; `core-js/stable` is core-js **3**, whose stable surface is genuinely
+ * larger — `globalThis`, `Object.fromEntries` and `URLSearchParams` are all
+ * new here. The extra weight is the upgrade, not waste.
+ *
+ * Switching to `useBuiltIns: 'usage'` would shrink the bundle a long way, and
+ * would be wrong: the README tells consumers to reach for `bundled.js`
+ * precisely when they have no polyfills of their own, so it has to keep
+ * shipping the full payload rather than only what bowser itself calls.
  */
 const legacyBabel = (useBuiltIns: false | 'entry') => babel({
   presets: [['@babel/preset-env', {