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fix(metro-resolver): Skip bare ext file resolution on ESM module resolution #1673

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fix(metro-resolver): Skip bare ext file resolution on ESM module resolution #1673

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335 changes: 335 additions & 0 deletions packages/metro-resolver/src/__tests__/esm-resolution-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 type {ResolutionContext} from '../index';

import {createPackageAccessors, createResolutionContext} from './utils';

const Resolver = require('../index');

describe('ESM bare specifier resolution skips sibling file lookups in node_modules', () => {
const fileMap = {
'/root/src/main.js': '',
// A normal package with package.json and main entry
'/root/node_modules/invariant/package.json': JSON.stringify({
name: 'invariant',
main: 'index.js',
}),
'/root/node_modules/invariant/index.js': '',
'/root/node_modules/invariant/lib/utils.js': '',
// A file sitting directly in node_modules (CJS pattern)
'/root/node_modules/invariant.web.js': '',
'/root/node_modules/invariant.js': '',
// Scoped package
'/root/node_modules/@scope/pkg/package.json': JSON.stringify({
name: '@scope/pkg',
main: 'index.js',
}),
'/root/node_modules/@scope/pkg/index.js': '',
'/root/node_modules/@scope/pkg/utils.js': '',
// Platform-specific file as sibling to scoped package dir
'/root/node_modules/@scope/pkg.web.js': '',
};

const baseContext: ResolutionContext = {
...createResolutionContext(fileMap),
originModulePath: '/root/src/main.js',
};

describe('bare package import (no subpath)', () => {
test('CJS resolves bare import to sibling file when it exists', () => {
// In CJS, resolveFile runs first, finding invariant.js as a sibling
expect(
Resolver.resolve(
{...baseContext, isESMImport: false},
'invariant',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant.js',
});
});

test('ESM resolves bare import via package.json main, not sibling file', () => {
// In ESM, resolveFile is skipped for bare package root imports,
// so it falls through to resolvePackageEntryPoint
expect(
Resolver.resolve(
{...baseContext, isESMImport: true},
'invariant',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant/index.js',
});
});

test('ESM does not resolve to a sibling file like node_modules/invariant.web.js', () => {
// Remove the package directory to force file fallback
const fileMapNoDir = {
'/root/src/main.js': '',
'/root/node_modules/invariant.web.js': '',
'/root/node_modules/invariant.js': '',
};

const context: ResolutionContext = {
...createResolutionContext(fileMapNoDir),
originModulePath: '/root/src/main.js',
isESMImport: true,
};

// ESM should NOT resolve bare 'invariant' to node_modules/invariant.js
expect(() => Resolver.resolve(context, 'invariant', null)).toThrow();
});

test('CJS can resolve to a standalone file in node_modules', () => {
const fileMapNoDir = {
'/root/src/main.js': '',
'/root/node_modules/invariant.web.js': '',
'/root/node_modules/invariant.js': '',
};

const context: ResolutionContext = {
...createResolutionContext(fileMapNoDir),
originModulePath: '/root/src/main.js',
isESMImport: false,
};

// CJS should still resolve bare 'invariant' to node_modules/invariant.js
expect(Resolver.resolve(context, 'invariant', null)).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant.js',
});
});

test('ESM does not try platform extensions as sibling files for bare import', () => {
const fileSystemLookup = jest.fn(baseContext.fileSystemLookup);
const context: ResolutionContext = {
...baseContext,
fileSystemLookup,
isESMImport: true,
};

Resolver.resolve(context, 'invariant', null);

// Should NOT have looked up any of these sibling file paths
const lookedUpPaths = fileSystemLookup.mock.calls.map(c => c[0]);
expect(lookedUpPaths).not.toContain(
'/root/node_modules/invariant.web.js',
);
expect(lookedUpPaths).not.toContain('/root/node_modules/invariant.js');
expect(lookedUpPaths).not.toContain(
'/root/node_modules/invariant.native.js',
);
// But should have looked up the directory
expect(lookedUpPaths).toContain('/root/node_modules');
});

test('CJS tries file extensions as sibling files for bare import', () => {
const fileSystemLookup = jest.fn(baseContext.fileSystemLookup);
const context: ResolutionContext = {
...baseContext,
fileSystemLookup,
isESMImport: false,
};

Resolver.resolve(context, 'invariant', null);

// CJS should try sibling file paths (even though the package resolves
// first in this case, the file resolution runs in resolveModulePath)
const lookedUpPaths = fileSystemLookup.mock.calls.map(c => c[0]);
// The invariant directory exists as a package, so resolveFile is called
// within resolveModulePath - it looks for the bare file first
expect(lookedUpPaths).toContain('/root/node_modules/invariant');
});
});

describe('scoped bare package import', () => {
test('ESM resolves scoped package via package.json main', () => {
expect(
Resolver.resolve(
{...baseContext, isESMImport: true},
'@scope/pkg',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/@scope/pkg/index.js',
});
});

test('ESM does not try file extensions on scoped package name', () => {
const fileSystemLookup = jest.fn(baseContext.fileSystemLookup);
const context: ResolutionContext = {
...baseContext,
fileSystemLookup,
isESMImport: true,
};

Resolver.resolve(context, '@scope/pkg', null);

const lookedUpPaths = fileSystemLookup.mock.calls.map(c => c[0]);
expect(lookedUpPaths).not.toContain(
'/root/node_modules/@scope/pkg.web.js',
);
expect(lookedUpPaths).not.toContain('/root/node_modules/@scope/pkg.js');
});
});

describe('subpath import (not package root)', () => {
test('ESM resolves subpath with file extensions', () => {
expect(
Resolver.resolve(
{...baseContext, isESMImport: true},
'invariant/lib/utils',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant/lib/utils.js',
});
});

test('CJS resolves subpath with file extensions', () => {
expect(
Resolver.resolve(
{...baseContext, isESMImport: false},
'invariant/lib/utils',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant/lib/utils.js',
});
});

test('ESM subpath import still tries platform extensions inside the package', () => {
const fileMapWithPlatform = {
...fileMap,
'/root/node_modules/invariant/lib/utils.web.js': '',
};

const context: ResolutionContext = {
...createResolutionContext(fileMapWithPlatform),
originModulePath: '/root/src/main.js',
isESMImport: true,
};

expect(Resolver.resolve(context, 'invariant/lib/utils', 'web')).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/invariant/lib/utils.web.js',
});
});

test('ESM scoped subpath import resolves with file extensions', () => {
expect(
Resolver.resolve(
{...baseContext, isESMImport: true},
'@scope/pkg/utils',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/@scope/pkg/utils.js',
});
});
});

describe('with package exports enabled', () => {
const exportsFileMap = {
'/root/src/main.js': '',
'/root/node_modules/pkg-with-exports/package.json': JSON.stringify({
name: 'pkg-with-exports',
main: 'lib/index.js',
exports: {
'.': './lib/index.js',
'./utils': './lib/utils.js',
},
}),
'/root/node_modules/pkg-with-exports/lib/index.js': '',
'/root/node_modules/pkg-with-exports/lib/utils.js': '',
// A sibling file that should never be picked
'/root/node_modules/pkg-with-exports.js': '',
};

const exportsContext: ResolutionContext = {
...createResolutionContext(exportsFileMap),
...createPackageAccessors(exportsFileMap),
originModulePath: '/root/src/main.js',
unstable_enablePackageExports: true,
};

test('ESM resolves via exports field, not sibling file', () => {
expect(
Resolver.resolve(
{...exportsContext, isESMImport: true},
'pkg-with-exports',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/pkg-with-exports/lib/index.js',
});
});

test('ESM subpath resolves via exports field', () => {
expect(
Resolver.resolve(
{...exportsContext, isESMImport: true},
'pkg-with-exports/utils',
null,
),
).toEqual({
type: 'sourceFile',
filePath: '/root/node_modules/pkg-with-exports/lib/utils.js',
});
});
});

describe('relative and absolute imports are unaffected', () => {
const relFileMap = {
'/root/src/main.js': '',
'/root/src/utils.js': '',
'/root/src/utils.web.js': '',
};

const relContext: ResolutionContext = {
...createResolutionContext(relFileMap),
originModulePath: '/root/src/main.js',
};

test('ESM relative import still tries platform extensions', () => {
expect(
Resolver.resolve({...relContext, isESMImport: true}, './utils', 'web'),
).toEqual({
type: 'sourceFile',
filePath: '/root/src/utils.web.js',
});
});

test('ESM absolute import still tries platform extensions', () => {
expect(
Resolver.resolve(
{...relContext, isESMImport: true},
'/root/src/utils',
'web',
),
).toEqual({
type: 'sourceFile',
filePath: '/root/src/utils.web.js',
});
});
});
});
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