test: metro-compat resolution tests

.prettierignore

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+metro-compat-test/**/__tests__/

.vscode/settings.json

@@ -1,3 +1,4 @@
 {
-  "css.validate": false
-}
+  "css.validate": false,
+  "editor.defaultFormatter": "esbenp.prettier-vscode"
+}

metro-compat-test/.eslintrc.js

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+module.exports = {
+  extends: '@callstack/eslint-config/node',
+  parserOptions: {
+    project: true,
+    tsconfigRootDir: __dirname,
+  },
+  ignorePatterns: [
+    '.eslintrc.js',
+    'babel.config.js',
+    'jest.config.js',
+    'jest.setup.js',
+    '**/__tests__/*.js',
+  ],
+  rules: {
+    'import/no-extraneous-dependencies': 'off',
+  },
+  settings: {
+    jest: {
+      version: 'latest',
+    },
+  },
+  overrides: [
+    {
+      files: ['jest.setup.js'],
+      env: {
+        jest: true,
+      },
+    },
+  ],
+};

metro-compat-test/.prettierrc.js

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+module.exports = {
+  singleQuote: true,
+  trailingComma: 'es5',
+};

metro-compat-test/README.md

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+# metro-compat-test
+
+## Description
+
+`metro-compat-test` is a package that uses the test suites from `metro-resolver` to ensure compatibility with `metro`, adapting them to work with `enhanced-resolve`.
+
+## Adherence to metro spec
+
+Some test suites are skipped altogether:
+
+- `assets-test.js` - because `enhanced-resolve`, like node resolution, returns only a single entry, it's impossible to support these test cases. We handle this differently using `AssetResolver` which provides you with first matching entry for development, but all scales are exposed to the runtime.
+- `index-test.js` - this suite contains some basic tests & failure tests which we could include but most of it contains tests for unsupported features like:
+  - `resolveRequest`
+  - `redirectModulePath`
+  - `disableHierarchicalLookup`
+
+Some test cases are skipped (all come from `package-exports-test.js`):
+
+- `[nonstrict]` tests are skipped because we don't support fallback in form of legacy file resolution
+- asset tests with package exports enabled are skipped because they are handled differently.
+- rest of the test skipped are due to inline snapshot not matching up with what `enhanced-resolve` returns
+
+## Updating Tests
+
+To update the tests, copy the latest test suites from the `metro-resolver/src/__tests__` directory in the [metro repository](https://github.com/facebook/metro/tree/main/packages/metro-resolver/src/__tests__) and paste them into `resolver/__tests__` dir.

metro-compat-test/babel.config.js

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+// based on https://github.com/facebook/metro/blob/main/babel.config.js
+const path = require('path');
+
+const pathMap = {
+  resolver: {
+    '../index': './resolve.ts',
+    '../errors/FailedToResolvePathError': './resolve-error.ts',
+    // ignored
+    '../types': '../types',
+  },
+};
+
+const resolvePath = (sourcePath, currentFile) => {
+  const dir = path.basename(path.dirname(path.dirname(currentFile)));
+  if (sourcePath.startsWith('.') && pathMap[dir]?.[sourcePath]) {
+    return path.join(__dirname, dir, pathMap[dir][sourcePath]);
+  } else {
+    return require.resolve(sourcePath, { paths: [path.dirname(currentFile)] });
+  }
+};
+
+const jsPlugins = [
+  'babel-plugin-syntax-hermes-parser',
+  '@babel/plugin-transform-flow-strip-types',
+  '@babel/plugin-transform-modules-commonjs',
+  '@babel/plugin-syntax-class-properties',
+];
+
+const tsPlugins = [
+  '@babel/plugin-transform-typescript',
+  '@babel/plugin-transform-modules-commonjs',
+  '@babel/plugin-syntax-class-properties',
+];
+
+module.exports = {
+  babelrc: false,
+  browserslistConfigFile: false,
+  overrides: [
+    {
+      test: ['**/*.ts'],
+      plugins: tsPlugins.map((plugin) => require.resolve(plugin)),
+    },
+    {
+      test: ['**/*.js'],
+      plugins: [
+        ...jsPlugins.map((plugin) => require.resolve(plugin)),
+        [require.resolve('babel-plugin-module-resolver'), { resolvePath }],
+      ],
+    },
+  ],
+};

metro-compat-test/jest.config.js

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+module.exports = {
+  rootDir: __dirname,
+  testEnvironment: 'node',
+  testRegex: '__tests__/.*-test\\.js$',
+  testPathIgnorePatterns: [
+    '<rootDir>/node_modules/',
+    // assets-test are not compatible with webpack's enhanced-resolve
+    '<rootDir>/resolver/__tests__/assets-test.js',
+    // index-test are almost entirely for legacy metro features which are not supported
+    '<rootDir>/resolver/__tests__/index-test.js',
+  ],
+  transform: { '\\.[jt]s$': 'babel-jest' },
+  setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
+};

metro-compat-test/jest.setup.js

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+const testsToSkip = {
+  describe: new Set([
+    // unsupported in ehnanced-resolve as well
+    '[unsupported] exotic nested arrays',
+  ]),
+  test: new Set([
+    // Non-strict package exports are not supported
+    '[nonstrict] should fall back to "main" field resolution when file does not exist',
+    '[nonstrict] should fall back to "main" field resolution when "exports" is an invalid subpath',
+    '[nonstrict] should fall back to "browser" spec resolution and log inaccessible import warning',
+    '[nonstrict] should fall back and log warning for an invalid "exports" target value',
+    '[nonstrict] should fall back to "browser" spec resolution and log inaccessible import warning',
+    '[nonstrict] should fall back to "browser" spec resolution and log inaccessible import warning',
+    // Assets are handled differently in webpack
+    'should resolve assets using "exports" field and calling `resolveAsset`',
+    // Resolving fails as expected but error messages are different
+    'should use most specific pattern base',
+    'should throw FailedToResolvePathError when no conditions are matched',
+  ]),
+};
+
+// alias it to test
+Object.defineProperty(testsToSkip, 'it', testsToSkip.test);
+
+// trap call & check if test should be skipped
+const handler = {
+  apply(target, _, args) {
+    if (testsToSkip[target.name].has(args[0])) {
+      return target.skip(...args);
+    } else return target(...args);
+  },
+};
+
+global.describe = new Proxy(global.describe, handler);
+global.test = new Proxy(global.test, handler);
+global.it = global.test;
+
+// mock imported utils to gain access to __fileMap and __options
+jest.doMock('./resolver/__tests__/utils', () => {
+  const originalModule = jest.requireActual('./resolver/__tests__/utils');
+  return {
+    createPackageAccessors(...args) {
+      return {
+        ...originalModule.createPackageAccessors(...args),
+        __fileMapOverrides: args[0],
+      };
+    },
+    createResolutionContext(...args) {
+      return {
+        ...originalModule.createResolutionContext(...args),
+        __fileMap: args[0],
+        __options: args[1],
+      };
+    },
+  };
+});

metro-compat-test/package.json

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+{
+  "name": "metro-compat-test",
+  "description": "Metro compatibility tests",
+  "author": "Jakub Romańczyk <jakub.romanczyk@callstack.com>",
+  "license": "MIT",
+  "private": true,
+  "engineStrict": true,
+  "engines": {
+    "node": ">=18"
+  },
+  "scripts": {
+    "lint": "eslint .",
+    "test": "jest --noStackTrace",
+    "typecheck": "tsc"
+  },
+  "devDependencies": {
+    "@callstack/repack": "workspace:*",
+    "@types/jest": "^28.1.1",
+    "@types/node": "^18",
+    "babel-jest": "^28.1.1",
+    "babel-plugin-module-resolver": "^5.0.0",
+    "babel-plugin-syntax-hermes-parser": "^0.20.1",
+    "enhanced-resolve": "^5.16.0",
+    "eslint": "^8.53.0",
+    "jest": "^28.1.1",
+    "memfs": "^3.4.4",
+    "type-fest": "^4.12.0"
+  }
+}

metro-compat-test/resolver/__tests__/assets-test.js

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+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+'use strict';
+
+import Resolver from '../index';
+import {createResolutionContext} from './utils';
+import path from 'path';
+
+describe('asset resolutions', () => {
+  const baseContext = {
+    ...createResolutionContext({
+      '/root/project/index.js': '',
+      '/root/project/src/data.json': '',
+      '/root/project/assets/example.asset.json': '',
+      '/root/project/assets/icon.png': '',
+      '/root/project/assets/icon@2x.png': '',
+    }),
+    originModulePath: '/root/project/index.js',
+  };
+  const assetResolutions = ['1', '2'];
+  const resolveAsset = (
+    dirPath: string,
+    assetName: string,
+    extension: string,
+  ) => {
+    const basePath = dirPath + path.sep + assetName;
+    let assets = [
+      basePath + extension,
+      ...assetResolutions.map(
+        resolution => basePath + '@' + resolution + 'x' + extension,
+      ),
+    ];
+
+    assets = assets.filter(candidate => baseContext.doesFileExist(candidate));
+
+    return assets.length ? assets : null;
+  };
+
+  test('should resolve a path as an asset when matched against `assetExts`', () => {
+    const context = {
+      ...baseContext,
+      assetExts: new Set(['png']),
+      resolveAsset,
+    };
+
+    expect(Resolver.resolve(context, './assets/icon.png', null)).toEqual({
+      type: 'assetFiles',
+      filePaths: [
+        '/root/project/assets/icon.png',
+        '/root/project/assets/icon@2x.png',
+      ],
+    });
+  });
+
+  test('should resolve a path as an asset when matched against `assetExts` (overlap with `sourceExts`)', () => {
+    const context = {
+      ...baseContext,
+      assetExts: new Set(['asset.json']),
+      resolveAsset,
+      sourceExts: ['js', 'json'],
+    };
+
+    // Source file matching `sourceExts`
+    expect(Resolver.resolve(context, './src/data.json', null)).toEqual({
+      type: 'sourceFile',
+      filePath: '/root/project/src/data.json',
+    });
+
+    // Asset file matching more specific asset ext
+    expect(
+      Resolver.resolve(context, './assets/example.asset.json', null),
+    ).toEqual({
+      type: 'assetFiles',
+      filePaths: ['/root/project/assets/example.asset.json'],
+    });
+  });
+});