Fix selection of assets when assetExts include a multipart extension

Summary:
Resolves #937.

Previously, the matching of `resolver.assetExts` in the resolve and transform steps was based on `path.extname()`, which would only consider the final segment in a path split by a `'.'`. This meant the inability to configure and match multipart extensions in `assetExts`, such as `'.asset.json'`. The new implementation iterates over all possible file extensions.

Validated against:
- Internal test app.
- Sample repo with relevant Metro config.

Changelog: **[Fix]** `resolver.assetExts` will now match asset files for extension values that include a dot (`.`)

Reviewed By: motiz88

Differential Revision: D43737453

fbshipit-source-id: 150c3aaf3bd58c24cd1670cc1a46e8531c24acf7

Author: huntie

packages/metro-resolver/src/__tests__/assets-test.js

@@ -0,0 +1,86 @@
+/**
+ * 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 path from 'path';
+import Resolver from '../index';
+import {createResolutionContext} from './utils';
+
+describe('asset resolutions', () => {
+  const baseContext = {
+    ...createResolutionContext({
+      '/root/project/index.js': '',
+      '/root/project/src/data.json': '',
+      '/root/project/assets/example.asset.json': '',
+      '/root/project/assets/icon.png': '',
+      '/root/project/assets/[email protected]': '',
+    }),
+    originModulePath: '/root/project/index.js',
+  };
+  const assetResolutions = ['1', '2'];
+  const resolveAsset = (
+    dirPath: string,
+    assetName: string,
+    extension: string,
+  ) => {
+    const basePath = dirPath + path.sep + assetName;
+    let assets = [
+      basePath + extension,
+      ...assetResolutions.map(
+        resolution => basePath + '@' + resolution + 'x' + extension,
+      ),
+    ];
+
+    assets = assets.filter(candidate => baseContext.doesFileExist(candidate));
+
+    return assets.length ? assets : null;
+  };
+
+  test('should resolve a path as an asset when matched against `assetExts`', () => {
+    const context = {
+      ...baseContext,
+      assetExts: new Set(['png']),
+      resolveAsset,
+    };
+
+    expect(Resolver.resolve(context, './assets/icon.png', null)).toEqual({
+      type: 'assetFiles',
+      filePaths: [
+        '/root/project/assets/icon.png',
+        '/root/project/assets/[email protected]',
+      ],
+    });
+  });
+
+  test('should resolve a path as an asset when matched against `assetExts` (overlap with `sourceExts`)', () => {
+    const context = {
+      ...baseContext,
+      assetExts: new Set(['asset.json']),
+      resolveAsset,
+      sourceExts: ['js', 'json'],
+    };
+
+    // Source file matching `sourceExts`
+    expect(Resolver.resolve(context, './src/data.json', null)).toEqual({
+      type: 'sourceFile',
+      filePath: '/root/project/src/data.json',
+    });
+
+    // Asset file matching more specific asset ext
+    expect(
+      Resolver.resolve(context, './assets/example.asset.json', null),
+    ).toEqual({
+      type: 'assetFiles',
+      filePaths: ['/root/project/assets/example.asset.json'],
+    });
+  });
+});

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

@@ -19,5 +19,17 @@ export default function isAssetFile(
   filePath: string,
   assetExts: $ReadOnlySet<string>,
 ): boolean {
-  return assetExts.has(path.extname(filePath).slice(1));
+  const baseName = path.basename(filePath);
+
+  for (let i = baseName.length - 1; i >= 0; i--) {
+    if (baseName[i] === '.') {
+      const ext = baseName.slice(i + 1);
+
+      if (assetExts.has(ext)) {
+        return true;
+      }
+    }
+  }
+
+  return false;
 }