Resolver: Resolve the package of a directory once for all extension candidates

packages/metro-resolver/src/__tests__/package-scope-test.js

@@ -0,0 +1,222 @@
+/**
+ * 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
+ */
+
+import type {PackageForModule, ResolutionContext} from '../types';
+
+import * as Resolver from '../index';
+import {
+  createPackageAccessors,
+  createResolutionContext,
+  posixToSystemPath as p,
+} from './utils';
+
+// These pin the paths the resolver passes to `getPackageForModule` for each
+// kind of specifier, so that a change in lookups per resolution is deliberate.
+describe('package scope lookups', () => {
+  // The path the resolver asks about for the files in a directory
+  const filesIn = (dirPath: string) => p(dirPath + '/package.json');
+
+  const fileMap = {
+    [p('/root/package.json')]: JSON.stringify({name: 'root'}),
+    [p('/root/src/main.js')]: '',
+    [p('/root/src/foo.js')]: '',
+    [p('/root/src/lib/index.js')]: '',
+    [p('/root/node_modules/pkg/package.json')]: JSON.stringify({
+      name: 'pkg',
+      main: 'lib/index',
+      browser: {'./lib/redirected.js': './lib/other.js'},
+    }),
+    [p('/root/node_modules/pkg/lib/index.js')]: '',
+    [p('/root/node_modules/pkg/lib/sub.js')]: '',
+    [p('/root/node_modules/pkg/lib/other.js')]: '',
+    [p('/root/node_modules/nopkg/index.js')]: '',
+  };
+
+  let getPackageForModule: JestMockFn<[string], ?PackageForModule>;
+  let context: ResolutionContext;
+
+  function useFileMap(files: typeof fileMap) {
+    const accessors = createPackageAccessors(files);
+    getPackageForModule = jest.fn(accessors.getPackageForModule);
+    context = {
+      ...createResolutionContext(files),
+      ...accessors,
+      getPackageForModule,
+      originModulePath: p('/root/src/main.js'),
+    };
+  }
+
+  beforeEach(() => {
+    useFileMap(fileMap);
+  });
+
+  const lookedUpPaths = () =>
+    getPackageForModule.mock.calls.map(([modulePath]) => modulePath);
+
+  test('relative file, found after trying several extensions', () => {
+    expect(Resolver.resolve(context, './foo', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/src/foo.js'),
+    });
+    expect(lookedUpPaths()).toEqual([p('/root/src/foo'), filesIn('/root/src')]);
+  });
+
+  test('relative file, when its package.json is a package root', () => {
+    useFileMap({
+      ...fileMap,
+      // A package whose "browser" field must not apply to the files beside it
+      [p('/root/src/package.json/package.json')]: JSON.stringify({
+        name: 'stand-in',
+        browser: {'./foo.js': false},
+      }),
+    });
+    expect(Resolver.resolve(context, './foo', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/src/foo.js'),
+    });
+    // The stand-in is retried with another name
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/foo'),
+      filesIn('/root/src'),
+      filesIn('/root/src') + '_',
+    ]);
+  });
+
+  test('throws if the scope is never that of the stand-in file', () => {
+    getPackageForModule = jest.fn(() => ({
+      rootPath: p('/root'),
+      packageJson: {name: 'root'},
+      packageRelativePath: '',
+    }));
+    context = {...context, getPackageForModule};
+    expect(() => Resolver.resolve(context, './foo', 'ios')).toThrow(
+      `getPackageForModule(${JSON.stringify(filesIn('/root/src') + '__')}) ` +
+        'returned packageRelativePath "", which should end in ' +
+        '"package.json__".',
+    );
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/foo'),
+      filesIn('/root/src'),
+      filesIn('/root/src') + '_',
+      filesIn('/root/src') + '__',
+    ]);
+  });
+
+  test('relative file in the file system root', () => {
+    useFileMap({[p('/main.js')]: '', [p('/foo.js')]: ''});
+    context = {...context, originModulePath: p('/main.js')};
+    expect(Resolver.resolve(context, './foo', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/foo.js'),
+    });
+    expect(lookedUpPaths()).toEqual([p('/foo'), filesIn('')]);
+  });
+
+  test('relative file with an explicit extension', () => {
+    expect(Resolver.resolve(context, './foo.js', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/src/foo.js'),
+    });
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/foo.js'),
+      filesIn('/root/src'),
+    ]);
+  });
+
+  test('relative directory, resolved to its index', () => {
+    expect(Resolver.resolve(context, './lib', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/src/lib/index.js'),
+    });
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/lib'),
+      filesIn('/root/src'),
+      filesIn('/root/src/lib'),
+    ]);
+  });
+
+  test('package entry point', () => {
+    expect(Resolver.resolve(context, 'pkg', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/node_modules/pkg/lib/index.js'),
+    });
+    // The origin, the package directory (twice), `pkg` as a file in
+    // node_modules, and the entry point's directory.
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/main.js'),
+      p('/root/node_modules/pkg'),
+      p('/root/node_modules/pkg'),
+      filesIn('/root/node_modules'),
+      filesIn('/root/node_modules/pkg/lib'),
+    ]);
+  });
+
+  test('package subpath', () => {
+    expect(Resolver.resolve(context, 'pkg/lib/sub', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/node_modules/pkg/lib/sub.js'),
+    });
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/main.js'),
+      p('/root/node_modules/pkg/lib/sub'),
+      p('/root/node_modules/pkg/lib/sub'),
+      filesIn('/root/node_modules/pkg/lib'),
+    ]);
+  });
+
+  test('package subpath redirected by the "browser" field', () => {
+    expect(Resolver.resolve(context, 'pkg/lib/redirected', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/node_modules/pkg/lib/other.js'),
+    });
+    // The redirected path may be redirected again by its own scope
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/main.js'),
+      p('/root/node_modules/pkg/lib/redirected'),
+      p('/root/node_modules/pkg/lib/other.js'),
+      filesIn('/root/node_modules/pkg/lib'),
+    ]);
+  });
+
+  test('module under node_modules without a package.json', () => {
+    expect(Resolver.resolve(context, 'nopkg', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/node_modules/nopkg/index.js'),
+    });
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/main.js'),
+      p('/root/node_modules/nopkg'),
+      p('/root/node_modules/nopkg'),
+      filesIn('/root/node_modules'),
+      filesIn('/root/node_modules/nopkg'),
+    ]);
+  });
+
+  test('package subpath with package exports', () => {
+    useFileMap({
+      ...fileMap,
+      [p('/root/node_modules/pkg/package.json')]: JSON.stringify({
+        name: 'pkg',
+        exports: {'./sub': './lib/sub.js'},
+      }),
+    });
+    context = {...context, unstable_enablePackageExports: true};
+    expect(Resolver.resolve(context, 'pkg/sub', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/node_modules/pkg/lib/sub.js'),
+    });
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/main.js'),
+      p('/root/node_modules/pkg/sub'),
+      p('/root/node_modules/pkg/sub'),
+    ]);
+  });
+});

packages/metro-resolver/src/resolve.js

@@ -12,6 +12,7 @@
 import type {
   FileAndDirCandidates,
   FileCandidates,
+  PackageForModule,
   Resolution,
   ResolutionContext,
   Result,
@@ -31,6 +32,7 @@ import {
   getPackageEntryPoint,
   matchSubpathFromMainFields,
   redirectModulePath,
+  redirectPackageSubpath,
 } from './PackageResolve';
 import resolveAsset from './resolveAsset';
 import isAssetFile from './utils/isAssetFile';
@@ -743,7 +745,12 @@ function resolveFile(
 
   const candidateExts: Array<string> = [];
   const filePathPrefix = path.join(dirPath, fileName);
-  const sfContext = {...context, candidateExts, filePathPrefix};
+  const sfContext = {
+    ...context,
+    candidateExts,
+    filePathPrefix,
+    candidatePackageScope: getCandidatePackageScope(context, dirPath, fileName),
+  };
   const sourceFileResolution = resolveSourceFile(sfContext, platform);
   if (sourceFileResolution != null) {
     if (typeof sourceFileResolution === 'string') {
@@ -758,6 +765,9 @@ type SourceFileContext = Readonly<{
   ...ResolutionContext,
   candidateExts: Array<string>,
   filePathPrefix: string,
+  // The package scope of all candidates, with `packageRelativePath` that of
+  // `filePathPrefix`, or null if they have none.
+  candidatePackageScope: ?PackageForModule,
 }>;
 
 // Either a full path, or a restricted subset of Resolution.
@@ -829,9 +839,17 @@ function resolveSourceFileForExt(
   extension: string,
 ): SourceFileResolution {
   const filePath = `${context.filePathPrefix}${extension}`;
+  const {candidatePackageScope} = context;
   const redirectedPath =
     // Any redirections for the bare path have already happened
-    extension !== '' ? redirectModulePath(context, filePath) : filePath;
+    extension !== '' && candidatePackageScope != null
+      ? redirectPackageSubpath(
+          context,
+          filePath,
+          candidatePackageScope,
+          candidatePackageScope.packageRelativePath + extension,
+        )
+      : filePath;
   if (redirectedPath === false) {
     return {type: 'empty'};
   }
@@ -843,6 +861,59 @@ function resolveSourceFileForExt(
   return null;
 }
 
+// Stands in for every file in a directory when looking up their package scope.
+// Edge case: if `package.json` is itself a directory that is a package root,
+// we append `_` and try again, up to MAX_ANY_FILE_NAME_ATTEMPTS names.
+const ANY_FILE_NAME = 'package.json';
+const MAX_ANY_FILE_NAME_ATTEMPTS = 3;
+
+/**
+ * The package scope shared by the candidates `fileName` + extension in
+ * `dirPath`, with `packageRelativePath` that of `fileName`.
+ *
+ * Note that this can differ from the scope of `dirPath` itself, or of a
+ * directory named `fileName` - a package root is its own scope, and files
+ * directly in `node_modules` have none.
+ */
+function getCandidatePackageScope(
+  context: ResolutionContext,
+  dirPath: string,
+  fileName: string,
+): ?PackageForModule {
+  const dirPrefix = dirPath.endsWith(path.sep) ? dirPath : dirPath + path.sep;
+  let name = ANY_FILE_NAME;
+  for (let attempt = 1; ; attempt++) {
+    const modulePath = dirPrefix + name;
+    const pkg = context.getPackageForModule(modulePath);
+    if (pkg == null) {
+      return null;
+    }
+    const {packageRelativePath} = pkg;
+    const dirRelativeLength = packageRelativePath.length - name.length;
+    if (
+      packageRelativePath.endsWith(name) &&
+      (dirRelativeLength === 0 ||
+        packageRelativePath[dirRelativeLength - 1] === path.sep)
+    ) {
+      return {
+        ...pkg,
+        packageRelativePath:
+          packageRelativePath.slice(0, dirRelativeLength) + fileName,
+      };
+    }
+    // Otherwise this is the scope of something other than the files here,
+    // usually a package root named `name`.
+    if (attempt === MAX_ANY_FILE_NAME_ATTEMPTS) {
+      throw new Error(
+        `getPackageForModule(${JSON.stringify(modulePath)}) returned ` +
+          `packageRelativePath ${JSON.stringify(packageRelativePath)}, ` +
+          `which should end in ${JSON.stringify(name)}.`,
+      );
+    }
+    name += '_';
+  }
+}
+
 function isRelativeImport(filePath: string) {
   return /^[.][.]?(?:[/]|$)/.test(filePath);
 }

packages/metro-resolver/src/types.js

@@ -167,6 +167,18 @@ export type ResolutionContext = Readonly<{
    * for a given absolute candidate path (which need not exist), or null if
    * there is no package.json closer than the nearest node_modules directory.
    *
+   * A path through a symlinked directory checks the link's target, then
+   * continues up from the link's parent. A symlinked file is scoped by where
+   * the link is.
+   *
+   * A missing path takes the scope of its deepest existing ancestor, or null
+   * if the first missing segment is `node_modules`.
+   *
+   * For the scope of every file in a directory, the resolver asks about its
+   * `package.json` (which needn't exist).
+   *
+   * The resolver calls this a few times per resolution, so it should be cheap.
+   *
    * @deprecated See https://github.com/react/metro/commit/29c77bff31e2475a086bc3f04073f485da8f9ff0
    */
   getPackageForModule: (absoluteModulePath: string) => ?PackageForModule,