fix: support ESM app entrypoints in the universal shim

.gitignore

@@ -2,6 +2,7 @@ node_modules
 dist
 entry-asar/*.js*
 entry-asar/*.ts
+entry-asar/esm/*.mjs*
 *.app
 test/fixtures/apps
 coverage

entry-asar/esm/has-asar.mts

@@ -0,0 +1,34 @@
+import { app } from 'electron';
+import { createRequire } from 'node:module';
+import path from 'node:path';
+
+const require = createRequire(import.meta.url);
+
+if (process.arch === 'arm64') {
+  await setPaths('arm64');
+} else {
+  await setPaths('x64');
+}
+
+async function setPaths(platform: string) {
+  // This should return the full path, ending in something like
+  // Notion.app/Contents/Resources/app.asar
+  const appPath = app.getAppPath();
+  const asarFile = `app-${platform}.asar`;
+
+  // Maybe we'll handle this in Electron one day
+  if (path.basename(appPath) === 'app.asar') {
+    const platformAppPath = path.join(path.dirname(appPath), asarFile);
+
+    // This is an undocumented API. It exists.
+    app.setAppPath(platformAppPath);
+  }
+
+  process._archPath = require.resolve(`../${asarFile}`);
+  try {
+    await import(process._archPath);
+  } catch (err) {
+    console.error(err);
+    process.exit(1);
+  }
+}

entry-asar/esm/no-asar.mts

@@ -0,0 +1,34 @@
+import { app } from 'electron';
+import { createRequire } from 'node:module';
+import path from 'node:path';
+
+const require = createRequire(import.meta.url);
+
+if (process.arch === 'arm64') {
+  await setPaths('arm64');
+} else {
+  await setPaths('x64');
+}
+
+async function setPaths(platform: string) {
+  // This should return the full path, ending in something like
+  // Notion.app/Contents/Resources/app
+  const appPath = app.getAppPath();
+  const appFolder = `app-${platform}`;
+
+  // Maybe we'll handle this in Electron one day
+  if (path.basename(appPath) === 'app') {
+    const platformAppPath = path.join(path.dirname(appPath), appFolder);
+
+    // This is an undocumented private API. It exists.
+    app.setAppPath(platformAppPath);
+  }
+
+  process._archPath = require.resolve(`../${appFolder}`);
+  try {
+    await import(process._archPath);
+  } catch (err) {
+    console.error(err);
+    process.exit(1);
+  }
+}

entry-asar/esm/tsconfig.json

@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "module": "nodenext",
+    "moduleResolution": "nodenext",
+    "target": "es2022",
+    "lib": ["es2022"],
+    "sourceMap": true,
+    "strict": true,
+    "rootDir": ".",
+    "outDir": ".",
+    "types": ["node"],
+    "allowSyntheticDefaultImports": true,
+    "esModuleInterop": true,
+    "declaration": false,
+    "ignoreDeprecations": "6.0"
+  },
+  "include": ["*.mts", "../ambient.d.ts"],
+  "exclude": []
+}

package.json

@@ -20,15 +20,18 @@
   "files": [
     "dist/*",
     "entry-asar/*",
+    "entry-asar/esm/*",
     "!entry-asar/**/*.ts",
+    "!entry-asar/**/*.mts",
+    "!entry-asar/**/tsconfig.json",
     "README.md"
   ],
   "author": "Samuel Attard",
   "publishConfig": {
     "provenance": true
   },
   "scripts": {
-    "build": "tsc -p tsconfig.json && tsc -p tsconfig.entry-asar.json",
+    "build": "tsc -p tsconfig.json && tsc -p tsconfig.entry-asar.json && tsc -p entry-asar/esm/tsconfig.json",
     "build:docs": "typedoc",
     "lint": "oxfmt --check . && oxlint",
     "lint:fix": "oxfmt --write . && oxlint --fix",
@@ -44,6 +47,7 @@
     "@types/node": "~22.10.7",
     "@types/plist": "^3.0.4",
     "cross-zip": "^4.0.0",
+    "electron43": "npm:electron@^43.0.0",
     "husky": "^9.1.7",
     "lint-staged": "^16.1.0",
     "oxfmt": "^0.44.0",

src/asar-utils.ts

@@ -15,6 +15,11 @@ export enum AsarMode {
   HAS_ASAR,
 }
 
+export enum EntrypointModule {
+  ESM = 'esm',
+  CJS = 'cjs',
+}
+
 export type MergeASARsOptions = {
   x64AsarPath: string;
   arm64AsarPath: string;
@@ -36,6 +41,40 @@ export const detectAsarMode = async (appPath: string) => {
   return AsarMode.HAS_ASAR;
 };
 
+/**
+ * Determine an app entrypoint's module format from its package.json using
+ * Node's own resolution rules. Anything we cannot positively identify as ESM
+ * is treated as CJS, so we never ship an ESM shim on a guess.
+ */
+export const detectEntrypointModule = (packageJson: unknown): EntrypointModule => {
+  if (typeof packageJson !== 'object' || packageJson === null) {
+    return EntrypointModule.CJS;
+  }
+  const pj = packageJson as { main?: unknown; type?: unknown };
+  const main = typeof pj.main === 'string' && pj.main.length > 0 ? pj.main : 'index.js';
+  if (main.endsWith('.mjs')) return EntrypointModule.ESM;
+  if (main.endsWith('.cjs')) return EntrypointModule.CJS;
+  // .js / .json / .node / extensionless -> governed by the package "type" field
+  return pj.type === 'module' ? EntrypointModule.ESM : EntrypointModule.CJS;
+};
+
+/**
+ * Given the detected module format of each architecture's entrypoint, decide
+ * which shim to ship. Refuses to build a universal app when the two
+ * architectures disagree, since a single shim cannot satisfy both.
+ */
+export const resolveShimModule = (
+  x64: EntrypointModule,
+  arm64: EntrypointModule,
+): EntrypointModule => {
+  if (x64 !== arm64) {
+    throw new Error(
+      `Can't create universal binary: the x64 app entrypoint is ${x64.toUpperCase()} but the arm64 app entrypoint is ${arm64.toUpperCase()}. Both architectures must use the same module system (CommonJS or ESM).`,
+    );
+  }
+  return x64;
+};
+
 export const generateAsarIntegrity = (asarPath: string) => {
   return {
     algorithm: 'SHA256' as const,

src/index.ts

@@ -7,7 +7,15 @@
 import * as asar from '@electron/asar';
 import plist from 'plist';
 
-import { AsarMode, detectAsarMode, isUniversalMachO, mergeASARs } from './asar-utils.js';
+import {
+  AsarMode,
+  detectAsarMode,
+  detectEntrypointModule,
+  EntrypointModule,
+  isUniversalMachO,
+  mergeASARs,
+  resolveShimModule,
+} from './asar-utils.js';
 import {
   AppFile,
   AppFileType,
@@ -270,17 +278,37 @@
 
         const entryAsar = path.resolve(tmpDir, 'entry-asar');
         await fs.promises.mkdir(entryAsar, { recursive: true });
-        await fs.promises.cp(
-          path.resolve(import.meta.dirname, '..', 'entry-asar', 'no-asar.js'),
-          path.resolve(entryAsar, 'index.js'),
-        );
+
         let pj = JSON.parse(
           await fs.promises.readFile(
             path.resolve(opts.x64AppPath, 'Contents', 'Resources', 'app', 'package.json'),
             'utf8',
           ),
         );
-        pj.main = 'index.js';
+        const arm64Pj = JSON.parse(
+          await fs.promises.readFile(
+            path.resolve(opts.arm64AppPath, 'Contents', 'Resources', 'app', 'package.json'),
+            'utf8',
+          ),
+        );
+        const shimModule = resolveShimModule(
+          detectEntrypointModule(pj),
+          detectEntrypointModule(arm64Pj),
+        );
+
+        if (shimModule === EntrypointModule.ESM) {
+          await fs.promises.cp(
+            path.resolve(import.meta.dirname, '..', 'entry-asar', 'esm', 'no-asar.mjs'),
+            path.resolve(entryAsar, 'index.mjs'),
+          );
+          pj.main = 'index.mjs';
+        } else {
+          await fs.promises.cp(
+            path.resolve(import.meta.dirname, '..', 'entry-asar', 'no-asar.js'),
+            path.resolve(entryAsar, 'index.js'),
+          );
+          pj.main = 'index.js';
+        }
         await fs.promises.writeFile(
           path.resolve(entryAsar, 'package.json'),
           JSON.stringify(pj) + '\n',
@@ -353,19 +381,41 @@
 
         const entryAsar = path.resolve(tmpDir, 'entry-asar');
         await fs.promises.mkdir(entryAsar, { recursive: true });
-        await fs.promises.cp(
-          path.resolve(import.meta.dirname, '..', 'entry-asar', 'has-asar.js'),
-          path.resolve(entryAsar, 'index.js'),
-        );
+
         let pj = JSON.parse(
           (
             await asar.extractFile(
               path.resolve(opts.x64AppPath, 'Contents', 'Resources', 'app.asar'),
               'package.json',
             )
           ).toString('utf8'),
         );
-        pj.main = 'index.js';
+        const arm64Pj = JSON.parse(
+          asar
+            .extractFile(
+              path.resolve(opts.arm64AppPath, 'Contents', 'Resources', 'app.asar'),
+              'package.json',
+            )
+            .toString('utf8'),
+        );
+        const shimModule = resolveShimModule(
+          detectEntrypointModule(pj),
+          detectEntrypointModule(arm64Pj),
+        );
+
+        if (shimModule === EntrypointModule.ESM) {
+          await fs.promises.cp(
+            path.resolve(import.meta.dirname, '..', 'entry-asar', 'esm', 'has-asar.mjs'),
+            path.resolve(entryAsar, 'index.mjs'),
+          );
+          pj.main = 'index.mjs';
+        } else {
+          await fs.promises.cp(
+            path.resolve(import.meta.dirname, '..', 'entry-asar', 'has-asar.js'),
+            path.resolve(entryAsar, 'index.js'),
+          );
+          pj.main = 'index.js';
+        }
         await fs.promises.writeFile(
           path.resolve(entryAsar, 'package.json'),
           JSON.stringify(pj) + '\n',
@@ -385,10 +435,10 @@
       const x64PlistPath = path.resolve(opts.x64AppPath, plistFile.relativePath);
       const arm64PlistPath = path.resolve(opts.arm64AppPath, plistFile.relativePath);
 
       const { ElectronAsarIntegrity: x64Integrity, ...x64Plist } = plist.parse(
         await fs.promises.readFile(x64PlistPath, 'utf8'),
       ) as any;
       const { ElectronAsarIntegrity: arm64Integrity, ...arm64Plist } = plist.parse(
         await fs.promises.readFile(arm64PlistPath, 'utf8'),
       ) as any;
       if (JSON.stringify(x64Plist) !== JSON.stringify(arm64Plist)) {
@@ -420,7 +470,7 @@
     d('moving final universal app to target destination');
     await fs.promises.mkdir(path.dirname(opts.outAppPath), { recursive: true });
     await fsMove(tmpApp, opts.outAppPath);
   } catch (err) {
     throw err;
   } finally {
     await fs.promises.rm(tmpDir, { recursive: true, force: true });

test/detect-entrypoint.spec.ts

@@ -0,0 +1,85 @@
+import { describe, expect, it } from 'vitest';
+
+import { detectEntrypointModule, EntrypointModule, resolveShimModule } from '../dist/asar-utils.js';
+
+describe('detectEntrypointModule', () => {
+  it('detects ESM when main has a .mjs extension', () => {
+    expect(detectEntrypointModule({ main: 'index.mjs' })).toBe(EntrypointModule.ESM);
+  });
+
+  it('detects ESM for a nested .mjs main', () => {
+    expect(detectEntrypointModule({ main: 'src/app.mjs' })).toBe(EntrypointModule.ESM);
+  });
+
+  it('detects CJS when main has a .cjs extension', () => {
+    expect(detectEntrypointModule({ main: 'index.cjs' })).toBe(EntrypointModule.CJS);
+  });
+
+  it('lets the .cjs extension win over a "module" type', () => {
+    expect(detectEntrypointModule({ main: 'index.cjs', type: 'module' })).toBe(
+      EntrypointModule.CJS,
+    );
+  });
+
+  it('lets the .mjs extension win over a "commonjs" type', () => {
+    expect(detectEntrypointModule({ main: 'index.mjs', type: 'commonjs' })).toBe(
+      EntrypointModule.ESM,
+    );
+  });
+
+  it('detects ESM for a .js main when type is "module"', () => {
+    expect(detectEntrypointModule({ main: 'index.js', type: 'module' })).toBe(EntrypointModule.ESM);
+  });
+
+  it('detects CJS for a .js main when type is "commonjs"', () => {
+    expect(detectEntrypointModule({ main: 'index.js', type: 'commonjs' })).toBe(
+      EntrypointModule.CJS,
+    );
+  });
+
+  it('defaults a .js main with no type to CJS', () => {
+    expect(detectEntrypointModule({ main: 'index.js' })).toBe(EntrypointModule.CJS);
+  });
+
+  it('detects ESM when type is "module" and there is no main', () => {
+    expect(detectEntrypointModule({ type: 'module' })).toBe(EntrypointModule.ESM);
+  });
+
+  it('defaults an empty package.json to CJS', () => {
+    expect(detectEntrypointModule({})).toBe(EntrypointModule.CJS);
+  });
+
+  it('treats null as CJS', () => {
+    expect(detectEntrypointModule(null)).toBe(EntrypointModule.CJS);
+  });
+
+  it('treats a non-object as CJS', () => {
+    expect(detectEntrypointModule(42)).toBe(EntrypointModule.CJS);
+  });
+});
+
+describe('resolveShimModule', () => {
+  it('returns CJS when both arches are CJS', () => {
+    expect(resolveShimModule(EntrypointModule.CJS, EntrypointModule.CJS)).toBe(
+      EntrypointModule.CJS,
+    );
+  });
+
+  it('returns ESM when both arches are ESM', () => {
+    expect(resolveShimModule(EntrypointModule.ESM, EntrypointModule.ESM)).toBe(
+      EntrypointModule.ESM,
+    );
+  });
+
+  it('throws when x64 is ESM but arm64 is CJS', () => {
+    expect(() => resolveShimModule(EntrypointModule.ESM, EntrypointModule.CJS)).toThrow(
+      /ESM[\s\S]*CJS/,
+    );
+  });
+
+  it('throws when x64 is CJS but arm64 is ESM', () => {
+    expect(() => resolveShimModule(EntrypointModule.CJS, EntrypointModule.ESM)).toThrow(
+      /CJS[\s\S]*ESM/,
+    );
+  });
+});