Resolver: Redirect a directory candidate through its own package scope

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

@@ -90,6 +90,28 @@ describe('package scope lookups', () => {
     ]);
   });
 
+  test('relative file, when a candidate is a package root', () => {
+    useFileMap({
+      ...fileMap,
+      // A package whose "browser" field applies to its own directory
+      [p('/root/src/bar.js/package.json')]: JSON.stringify({
+        name: 'bar.js',
+        browser: {'./': './replacement.js'},
+      }),
+      [p('/root/src/bar.js/replacement.js')]: '',
+    });
+    expect(Resolver.resolve(context, './bar', 'ios')).toEqual({
+      type: 'sourceFile',
+      filePath: p('/root/src/bar.js/replacement.js'),
+    });
+    // The directory candidate is looked up as a module of its own
+    expect(lookedUpPaths()).toEqual([
+      p('/root/src/bar'),
+      filesIn('/root/src'),
+      p('/root/src/bar.js'),
+    ]);
+  });
+
   test('throws if the scope is never that of the stand-in file', () => {
     getPackageForModule = jest.fn(() => ({
       rootPath: p('/root'),

packages/metro-resolver/src/resolve.js

@@ -839,21 +839,29 @@ 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 !== '' && candidatePackageScope != null
-      ? redirectPackageSubpath(
-          context,
-          filePath,
-          candidatePackageScope,
-          candidatePackageScope.packageRelativePath + extension,
-        )
-      : filePath;
-  if (redirectedPath === false) {
-    return {type: 'empty'};
+  let lookupResult = context.fileSystemLookup(filePath);
+  // Any redirections for the bare path have already happened
+  if (extension !== '') {
+    const {candidatePackageScope} = context;
+    const redirectedPath =
+      lookupResult.exists && lookupResult.type === 'd'
+        ? // A directory may be a package root, i.e. its own package scope
+          redirectModulePath(context, filePath)
+        : candidatePackageScope != null
+          ? redirectPackageSubpath(
+              context,
+              filePath,
+              candidatePackageScope,
+              candidatePackageScope.packageRelativePath + extension,
+            )
+          : filePath;
+    if (redirectedPath === false) {
+      return {type: 'empty'};
+    }
+    if (redirectedPath !== filePath) {
+      lookupResult = context.fileSystemLookup(redirectedPath);
+    }
   }
-  const lookupResult = context.fileSystemLookup(redirectedPath);
   if (lookupResult.exists && lookupResult.type === 'f') {
     return lookupResult.realPath;
   }