Update exports resolution to ignore absolute and relative imports

Summary: Changelog: **[Experimental]** Fix bug where `"exports"` field would be used on relative imports within a package

Reviewed By: motiz88

Differential Revision: D43665370

fbshipit-source-id: dfed117b0f6d6e8bed1469cb2ece0f241cf079e7

Author: huntie

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

@@ -243,6 +243,7 @@ describe('with package exports resolution enabled', () => {
             '.': './index.js',
             './foo.js': './lib/foo.js',
             './baz': './node_modules/baz/index.js',
+            './metadata.json': './metadata.min.json',
           },
         }),
         '/root/node_modules/test-pkg/index.js': '',
@@ -253,6 +254,8 @@ describe('with package exports resolution enabled', () => {
         '/root/node_modules/test-pkg/lib/foo.ios.js': '',
         '/root/node_modules/test-pkg/private/bar.js': '',
         '/root/node_modules/test-pkg/node_modules/baz/index.js': '',
+        '/root/node_modules/test-pkg/metadata.json': '',
+        '/root/node_modules/test-pkg/metadata.min.json': '',
       }),
       originModulePath: '/root/src/main.js',
       unstable_enablePackageExports: true,
@@ -305,6 +308,31 @@ describe('with package exports resolution enabled', () => {
       `);
     });
 
+    test('should not use "exports" for internal relative imports within a package', () => {
+      const context = {
+        ...baseContext,
+        originModulePath: '/root/node_modules/test-pkg/lib/foo.js',
+      };
+
+      expect(Resolver.resolve(context, '../metadata.json', null)).toEqual({
+        type: 'sourceFile',
+        filePath: '/root/node_modules/test-pkg/metadata.json',
+      });
+    });
+
+    test('should not use "exports" for an absolute import path', () => {
+      expect(
+        Resolver.resolve(
+          baseContext,
+          '/root/node_modules/test-pkg/metadata.json',
+          null,
+        ),
+      ).toEqual({
+        type: 'sourceFile',
+        filePath: '/root/node_modules/test-pkg/metadata.json',
+      });
+    });
+
     describe('should resolve "exports" target directly', () => {
       test('without expanding `sourceExts`', () => {
         expect(Resolver.resolve(baseContext, 'test-pkg/foo.js', null)).toEqual({
@@ -374,13 +402,15 @@ describe('with package exports resolution enabled', () => {
           name: 'test-pkg',
           main: 'index.js',
           exports: {
+            '.': './src/index.js',
             './features/*.js': './src/features/*.js',
             './features/bar/*.js': {
               'react-native': null,
             },
             './assets/*': './assets/*',
           },
         }),
+        '/root/node_modules/test-pkg/src/index.js': '',
         '/root/node_modules/test-pkg/src/features/foo.js': '',
         '/root/node_modules/test-pkg/src/features/foo.js.js': '',
         '/root/node_modules/test-pkg/src/features/bar/Bar.js': '',

packages/metro-resolver/src/resolve.js

@@ -50,7 +50,7 @@ function resolve(
   }
 
   if (isRelativeImport(moduleName) || path.isAbsolute(moduleName)) {
-    const result = resolvePackage(context, moduleName, platform);
+    const result = resolveModulePath(context, moduleName, platform);
     if (result.type === 'failed') {
       throw new FailedToResolvePathError(result.candidates);
     }
@@ -78,7 +78,7 @@ function resolve(
       originModulePath.indexOf(path.sep, fromModuleParentIdx),
     );
     const absPath = path.join(originModuleDir, realModuleName);
-    const result = resolvePackage(context, absPath, platform);
+    const result = resolveModulePath(context, absPath, platform);
     if (result.type === 'failed') {
       throw new FailedToResolvePathError(result.candidates);
     }
@@ -240,10 +240,11 @@ class MissingFileInHastePackageError extends Error {
 }
 
 /**
- * In the NodeJS-style module resolution scheme we want to check potential
- * paths both as directories and as files. For example, `/foo/bar` may resolve
- * to `/foo/bar.js` (preferred), but it might also be `/foo/bar/index.js`, or
- * even a package directory.
+ * Resolve a package entry point or subpath target.
+ *
+ * This should be used when resolving a bare import specifier prefixed with the
+ * package name. Use `resolveModulePath` instead to scope to legacy "browser"
+ * spec behaviour, which is also applicable to relative and absolute imports.
  */
 function resolvePackage(
   context: ResolutionContext,