feat!: replace hybrid CJS/ESM build with ESM-only

.yarn/patches/@metamask-safe-event-emitter-npm-3.1.1-a7872b1f5a.patch

@@ -0,0 +1,24 @@
+diff --git a/dist/esm/index.d.mts b/dist/esm/index.d.mts
+new file mode 100644
+index 0000000000000000000000000000000000000000..d48ab7ade4e48f566f3ca48c60636368919b1044
+--- /dev/null
++++ b/dist/esm/index.d.mts
+@@ -0,0 +1,5 @@
++/// <reference types="node" />
++import { EventEmitter } from 'events';
++export default class SafeEventEmitter extends EventEmitter {
++    emit(type: string, ...args: any[]): boolean;
++}
+diff --git a/package.json b/package.json
+index 87ca2f6363c43d2f9d45be268e8ba03c1669c02c..72211f17fe3976ef8dac7d8512d60a6de1275fbd 100644
+--- a/package.json
++++ b/package.json
+@@ -8,7 +8,7 @@
+   "exports": {
+     ".": {
+       "import": {
+-        "types": "./dist/esm/index.d.ts",
++        "types": "./dist/esm/index.d.mts",
+         "default": "./dist/esm/index.mjs"
+       },
+       "require": {

.yarnrc.yml

@@ -27,7 +27,6 @@ npmPreapprovedPackages:
   - "@metamask/*"
   - "@metamask-previews/*"
   - "@lavamoat/*"
-  - "@ts-bridge/*"
 
 plugins:
   - path: .yarn/plugins/@yarnpkg/plugin-allow-scripts.cjs

docs/processes/building.md

@@ -1,7 +1,5 @@
 # Building packages
 
-[`ts-bridge`](https://github.com/ts-bridge/ts-bridge) is used to build packages in both CommonJS- and ESM-compatible formats.
-
 Built files show up in the `dist/` directory in each package. These are the files which will ultimately be published to NPM.
 
 - Run `yarn build` to build all packages in the monorepo.

eslint-suppressions.json

@@ -14,9 +14,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 7
     },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 1
-    },
     "no-negated-condition": {
       "count": 3
     },
@@ -251,9 +248,6 @@
   "packages/assets-controllers/src/DeFiPositionsController/DeFiPositionsController.ts": {
     "@typescript-eslint/explicit-function-return-type": {
       "count": 2
-    },
-    "@typescript-eslint/no-misused-promises": {
-      "count": 2
     }
   },
   "packages/assets-controllers/src/DeFiPositionsController/group-defi-positions.ts": {
@@ -289,9 +283,6 @@
     }
   },
   "packages/assets-controllers/src/MultichainBalancesController/MultichainBalancesController.ts": {
-    "@typescript-eslint/no-misused-promises": {
-      "count": 1
-    },
     "no-restricted-syntax": {
       "count": 2
     }
@@ -311,12 +302,6 @@
     "@typescript-eslint/naming-convention": {
       "count": 5
     },
-    "@typescript-eslint/no-misused-promises": {
-      "count": 2
-    },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 6
-    },
     "@typescript-eslint/prefer-optional-chain": {
       "count": 1
     },
@@ -475,9 +460,6 @@
     "@typescript-eslint/no-unused-vars": {
       "count": 1
     },
-    "@typescript-eslint/prefer-optional-chain": {
-      "count": 3
-    },
     "id-length": {
       "count": 1
     },
@@ -601,9 +583,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 25
     },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 1
-    },
     "no-negated-condition": {
       "count": 1
     }
@@ -1288,9 +1267,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 1
     },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 2
-    },
     "id-denylist": {
       "count": 1
     }
@@ -1377,9 +1353,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 4
     },
-    "@typescript-eslint/no-misused-promises": {
-      "count": 2
-    },
     "no-restricted-syntax": {
       "count": 1
     }
@@ -1739,9 +1712,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 4
     },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 4
-    },
     "id-length": {
       "count": 2
     },
@@ -2105,9 +2075,6 @@
     "@typescript-eslint/explicit-function-return-type": {
       "count": 7
     },
-    "@typescript-eslint/no-base-to-string": {
-      "count": 1
-    },
     "@typescript-eslint/no-unused-vars": {
       "count": 2
     },
@@ -2131,7 +2098,7 @@
       "count": 10
     },
     "@typescript-eslint/no-floating-promises": {
-      "count": 4
+      "count": 3
     },
     "no-restricted-syntax": {
       "count": 4
@@ -2240,11 +2207,6 @@
       "count": 2
     }
   },
-  "packages/transaction-pay-controller/src/strategy/bridge/bridge-submit.ts": {
-    "no-restricted-syntax": {
-      "count": 1
-    }
-  },
   "packages/transaction-pay-controller/src/strategy/relay/hyperliquid-withdraw.ts": {
     "no-restricted-syntax": {
       "count": 1

eslint.config.mjs

@@ -2,6 +2,7 @@ import base, { createConfig } from '@metamask/eslint-config';
 import jest from '@metamask/eslint-config-jest';
 import nodejs from '@metamask/eslint-config-nodejs';
 import typescript from '@metamask/eslint-config-typescript';
+import node from 'eslint-plugin-n';
 
 const NODE_LTS_VERSION = 22;
 
@@ -94,6 +95,9 @@ const config = createConfig([
       // Handled by Oxfmt.
       'prettier/prettier': 'off',
       'import-x/order': 'off',
+      // Allow `void somePromise()` to explicitly mark ignored promises
+      // (required by `no-floating-promises`).
+      'no-void': ['error', { allowAsStatement: true }],
     },
   },
   {
@@ -125,7 +129,7 @@ const config = createConfig([
   {
     files: ['**/*.{js,cjs}'],
     languageOptions: {
-      sourceType: 'script',
+      sourceType: 'module',
       ecmaVersion: 2020,
     },
   },
@@ -179,6 +183,13 @@ const config = createConfig([
       'jest/no-alias-methods': 'error',
       'jest/no-commented-out-tests': 'error',
       'jest/no-disabled-tests': 'error',
+
+      // Some package types are wrong (e.g., nock).
+      'import-x/no-named-as-default-member': 'off',
+
+      // `import { jest } from '@jest/globals'` is required in ESM test files
+      // and intentionally shadows the Jest-injected global.
+      '@typescript-eslint/no-shadow': ['error', { allow: ['jest'] }],
     },
     settings: {
       node: {
@@ -218,6 +229,19 @@ const config = createConfig([
       'n/hashbang': 'off',
     },
   },
+  {
+    files: [
+      '**/*.cjs',
+      '**/.prettierrc.js',
+      '**/.eslintrc.js',
+      '**/jest.config*.js',
+      '**/jest.environment.js',
+    ],
+    rules: {
+      // CJS config files have no import/export statements.
+      'import-x/unambiguous': 'off',
+    },
+  },
   {
     files: ['**/jest.environment.js'],
     rules: {
@@ -373,6 +397,33 @@ const config = createConfig([
       'n/no-process-env': 'off',
     },
   },
+
+  // ESM-specific configuration. We should port this to
+  // `@metamask/eslint-config` at some point.
+  {
+    plugins: { n: node },
+    rules: {
+      // `import-x/extensions` doesn't support using ".js" for TypeScript
+      // files(?), so we load the `n` plugin and use
+      // `n/file-extension-in-import` instead.
+      'n/file-extension-in-import': ['error', 'always'],
+      'import-x/extensions': [
+        'error',
+        {
+          js: 'ignorePackages',
+          ts: 'never',
+          tsx: 'never',
+          json: 'always',
+        },
+      ],
+      'import-x/no-useless-path-segments': [
+        'error',
+        {
+          noUselessIndex: false,
+        },
+      ],
+    },
+  },
 ]);
 
 export default config;

jest.config.packages.js

@@ -3,7 +3,16 @@
  * https://jestjs.io/docs/configuration
  */
 
-module.exports = {
+import { fileURLToPath } from 'node:url';
+import { createDefaultEsmPreset } from 'ts-jest';
+
+const presetConfig = createDefaultEsmPreset({
+  tsconfig: '<rootDir>/tsconfig.json',
+});
+
+const config = {
+  ...presetConfig,
+
   // All imported modules in your tests should be mocked automatically
   // automock: false,
 
@@ -77,20 +86,17 @@ module.exports = {
   // ],
 
   // A map from regular expressions to module names or to arrays of module names that allow to stub out resources with a single module
-  // Here we ensure that Jest resolves `@metamask/*` imports to the uncompiled source code for packages that live in this repo.
-  // NOTE: This must be synchronized with the `paths` option in `tsconfig.base.json`.
+  // NOTE: Monorepo `@metamask/*` packages are resolved to TypeScript source by `jest.resolver.cjs`.
+  // External `@metamask/*` packages are resolved by Jest's default resolver, which honours `exports` fields.
+  // NOTE: The `'^(\\..+)\\.js$'` entry must be synchronized with the `paths` option in `tsconfig.base.json`.
   moduleNameMapper: {
+    '^(\\..+)\\.js$': '$1',
     '^@metamask/json-rpc-engine/v2$': [
       '<rootDir>/../json-rpc-engine/src/v2/index.ts',
     ],
-    '^@metamask/utils/node$': require.resolve('@metamask/utils/node'),
-    '^@metamask/(.+)$': [
-      '<rootDir>/../$1/src',
-      // Some @metamask/* packages we are referencing aren't in this monorepo,
-      // so in that case use their published versions
-      '<rootDir>/../../node_modules/@metamask/$1',
-    ],
-    '^uuid$': require.resolve('uuid'),
+    '^@metamask/utils/node$': fileURLToPath(
+      import.meta.resolve('@metamask/utils/node'),
+    ),
   },
 
   // An array of regexp pattern strings, matched against all module paths before considered 'visible' to the module loader
@@ -103,11 +109,11 @@ module.exports = {
   // notifyMode: "failure-change",
 
   // A preset that is used as a base for Jest's configuration
-  preset: 'ts-jest',
+  // preset: 'ts-jest',
 
   // The path to the Prettier executable used to format snapshots
   // Jest doesn't support Prettier 3 yet, so we use Prettier 2
-  prettierPath: require.resolve('prettier-2'),
+  prettierPath: fileURLToPath(import.meta.resolve('prettier-2')),
 
   // Run tests from one or more projects
   // projects: undefined
@@ -123,7 +129,7 @@ module.exports = {
   // resetModules: false,
 
   // A path to a custom resolver
-  // resolver: undefined,
+  resolver: '../../jest.resolver.cjs',
 
   // "restoreMocks" restores all mocks created using jest.spyOn to their
   // original implementations, between each test. It does not affect mocked
@@ -208,3 +214,5 @@ module.exports = {
   // Whether to use watchman for file crawling
   // watchman: true,
 };
+
+export default config;

jest.resolver.cjs

@@ -0,0 +1,52 @@
+/* eslint-disable import-x/unambiguous, n/no-sync */
+'use strict';
+
+const { join, resolve } = require('path');
+const { existsSync, statSync } = require('fs');
+
+const REPO_ROOT = resolve(__dirname);
+const PACKAGES_DIR = join(REPO_ROOT, 'packages');
+
+/**
+ * Custom Jest resolver that redirects `@metamask/*` imports to monorepo source
+ * when the package exists locally, and falls back to default resolution (which
+ * honours the package `exports` field) for external packages.
+ *
+ * Without this, the `moduleNameMapper` fallback returns a directory path for
+ * external `@metamask/*` packages. Jest then uses `main` (CJS) rather than
+ * `exports.import` (ESM), causing class-inheritance failures at runtime.
+ *
+ * @param {string} moduleName - The module name to resolve.
+ * @param {object} options - Jest resolver options including `defaultResolver`.
+ * @returns {string} The resolved module path.
+ */
+module.exports = function resolver(moduleName, options) {
+  const { basedir, defaultResolver } = options;
+
+  // Skip the monorepo redirect when the import originates from an external
+  // package in node_modules. Those packages use CJS require() and cannot load
+  // ESM TypeScript source files — they must resolve against published dist.
+  const isFromNodeModules =
+    basedir !== undefined && basedir.includes('/node_modules/');
+
+  const match =
+    !isFromNodeModules && /^@metamask\/([^/]+)(\/.*)?$/u.exec(moduleName);
+
+  if (match) {
+    const [, pkgName, subPath = ''] = match;
+    const srcDir = join(PACKAGES_DIR, pkgName, 'src');
+
+    if (existsSync(srcDir)) {
+      let target = subPath ? join(srcDir, subPath) : join(srcDir, 'index.ts');
+      // If the resolved target is a directory, look for its index file.
+      if (existsSync(target) && statSync(target).isDirectory()) {
+        target = join(target, 'index.ts');
+      }
+
+      return defaultResolver(target, options);
+    }
+  }
+
+  // External package — use default resolver, which honours `exports` fields.
+  return defaultResolver(moduleName, options);
+};

knip.config.ts

@@ -279,6 +279,7 @@ const config: KnipConfig = {
     // follow-up.
     '@metamask/providers',
     'webextension-polyfill',
+    '@jest/globals',
   ],
 };