Fix exact "exports" and "imports" keys with no target falling back to a pattern

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

@@ -655,6 +655,45 @@ describe('with package exports resolution enabled', () => {
       });
     });
 
+    test.each([
+      ['null', 'internal'],
+      ['no matching condition', 'server'],
+    ])(
+      'exact subpath with %s target does not fall back to a pattern',
+      (_, subpath) => {
+        const logWarning = jest.fn();
+        const context = {
+          ...createResolutionContext({
+            '/root/src/main.js': '',
+            '/root/node_modules/test-pkg/package.json': JSON.stringify({
+              name: 'test-pkg',
+              exports: {
+                './*': './lib/*.js',
+                './internal': null,
+                './server': {browser: './server-browser.js'},
+              },
+            }),
+            '/root/node_modules/test-pkg/lib/internal.js': '',
+            '/root/node_modules/test-pkg/lib/server.js': '',
+            '/root/node_modules/test-pkg/internal.js': '',
+            '/root/node_modules/test-pkg/server.js': '',
+          }),
+          originModulePath: '/root/src/main.js',
+          unstable_enablePackageExports: true,
+          unstable_logWarning: logWarning,
+        };
+
+        expect(Resolver.resolve(context, `test-pkg/${subpath}`, null)).toEqual({
+          type: 'sourceFile',
+          filePath: `/root/node_modules/test-pkg/${subpath}.js`,
+        });
+        expect(logWarning).toHaveBeenCalledTimes(1);
+        expect(logWarning.mock.calls[0][0]).toContain(
+          `"/root/node_modules/test-pkg/${subpath}" which is listed in the "exports"`,
+        );
+      },
+    );
+
     describe('package encapsulation', () => {
       test('[nonstrict] should fall back to "browser" spec resolution and log inaccessible import warning', () => {
         const logWarning = jest.fn();

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

@@ -84,6 +84,31 @@ describe('import subpath patterns resolution support', () => {
       filePath: p('/root/node_modules/test-pkg/src/features/foo.js.js'),
     });
   });
+
+  test('exact subpath with a null or unmatched target does not fall back to a pattern', () => {
+    const logWarning = jest.fn();
+    const context = {
+      ...createResolutionContext({
+        [p('/root/node_modules/test-pkg/package.json')]: JSON.stringify({
+          name: 'test-pkg',
+          imports: {
+            '#features/*': './src/features/*.js',
+            '#features/foo': null,
+            '#features/bar': {browser: './src/features/bar.web.js'},
+          },
+        }),
+        [p('/root/node_modules/test-pkg/src/index.js')]: '',
+        [p('/root/node_modules/test-pkg/src/features/foo.js')]: '',
+        [p('/root/node_modules/test-pkg/src/features/bar.js')]: '',
+      }),
+      originModulePath: p('/root/node_modules/test-pkg/src/index.js'),
+      unstable_logWarning: logWarning,
+    };
+
+    expect(() => Resolver.resolve(context, '#features/foo', null)).toThrow();
+    expect(() => Resolver.resolve(context, '#features/bar', null)).toThrow();
+    expect(logWarning).toHaveBeenCalledTimes(2);
+  });
 });
 
 describe('import subpath conditional imports resolution', () => {

packages/metro-resolver/src/utils/matchSubpathFromExportsLike.js

@@ -49,11 +49,16 @@ export function matchSubpathFromExportsLike(
     createConfigError,
   );
 
-  let target = exportsLikeMapAfterConditions.get(subpath);
+  let target = null;
   let patternMatch = null;
 
-  // Attempt to match after expanding any subpath pattern keys
-  if (target == null) {
+  // Attempt to match subpath pattern keys only if there is no exact key. An
+  // exact key takes precedence even when its target is null. See step 2 of
+  // `PACKAGE_IMPORTS_EXPORTS_RESOLVE` in:
+  // https://nodejs.org/api/esm.html#resolution-algorithm-specification
+  if (exportsLikeMapAfterConditions.has(subpath)) {
+    target = exportsLikeMapAfterConditions.get(subpath);
+  } else {
     // Gather keys which are subpath patterns in descending order of specificity
     // For ordering, see `PATTERN_KEY_COMPARE` in:
     // https://nodejs.org/api/esm.html#resolution-algorithm-specification