fix(metro): Fix regression to allow scale assets to be resolved again for single asset requests

packages/metro/src/Assets.js

@@ -299,29 +299,36 @@ export async function getAsset(
   }
 
   // NOTE: If fileExistsInFileMap is not provided, we fall back to pathBelongsToRoots for backward compatibility, as getAsset is part of the public API.
-  if (fileExistsInFileMap != null) {
-    if (!fileExistsInFileMap(absolutePath)) {
-      throw new Error(
-        `'${relativePath}' could not be found, because it is not within the projectRoot or watchFolders, or it is blocked via the resolver.blockList config`,
-      );
-    }
-  } else {
-    if (!pathBelongsToRoots(absolutePath, [projectRoot, ...watchFolders])) {
-      throw new Error(
-        `'${relativePath}' could not be found, because it cannot be found in the project root or any watch folder`,
-      );
-    }
+  if (
+    fileExistsInFileMap == null &&
+    !pathBelongsToRoots(absolutePath, [projectRoot, ...watchFolders])
+  ) {
+    throw new Error(
+      `'${relativePath}' could not be found, because it cannot be found in the project root or any watch folder`,
+    );
   }
 
   const record = await getAbsoluteAssetRecord(absolutePath, platform ?? null);
 
   for (let i = 0; i < record.scales.length; i++) {
     if (record.scales[i] >= assetData.resolution) {
+      if (
+        fileExistsInFileMap != null &&
+        !fileExistsInFileMap(record.files[i])
+      ) {
+        continue;
+      }
       return fs.promises.readFile(record.files[i]);
     }
   }
 
-  return fs.promises.readFile(record.files[record.files.length - 1]);
+  const lastFile = record.files[record.files.length - 1];
+  if (fileExistsInFileMap != null && !fileExistsInFileMap(lastFile)) {
+    throw new Error(
+      `'${relativePath}' could not be found, because it is not within the projectRoot or watchFolders, or it is blocked via the resolver.blockList config`,
+    );
+  }
+  return fs.promises.readFile(lastFile);
 }
 
 function pathBelongsToRoots(

packages/metro/src/__tests__/Assets-test.js

@@ -166,6 +166,81 @@ describe('getAsset', () => {
       getAssetStr('imgs/b.png', '/root', [], null, ['png'], () => false),
     ).rejects.toBeInstanceOf(Error);
   });
+
+  test('should serve scale variant when only scale variants exist and fileExistsInFileMap is provided', async () => {
+    writeImages({
+      'b@2x.png': 'b2 image',
+      'b@3x.png': 'b3 image',
+    });
+
+    expect(
+      await getAssetStr(
+        'imgs/b@2x.png',
+        '/root',
+        [],
+        null,
+        ['png'],
+        () => true,
+      ),
+    ).toBe('b2 image');
+  });
+
+  test('should throw when fileExistsInFileMap rejects the resolved scale variant', async () => {
+    writeImages({
+      'b@2x.png': 'b2 image',
+      'b@3x.png': 'b3 image',
+    });
+
+    await expect(
+      getAssetStr('imgs/b@2x.png', '/root', [], null, ['png'], () => false),
+    ).rejects.toBeInstanceOf(Error);
+  });
+
+  test('should check fileExistsInFileMap against the resolved file, not the base path', async () => {
+    writeImages({
+      'b@2x.png': 'b2 image',
+      'b@3x.png': 'b3 image',
+    });
+
+    const checkedPaths = [];
+    const result = await getAssetStr(
+      'imgs/b@2x.png',
+      '/root',
+      [],
+      null,
+      ['png'],
+      filePath => {
+        checkedPaths.push(filePath);
+        return true;
+      },
+    );
+
+    expect(result).toBe('b2 image');
+    expect(checkedPaths).toEqual(['/root/imgs/b@2x.png']);
+  });
+
+  test('should check fileExistsInFileMap for the fallback (highest scale) file', async () => {
+    writeImages({
+      'b@1x.png': 'b1 image',
+      'b@2x.png': 'b2 image',
+    });
+
+    const checkedPaths = [];
+    const result = await getAssetStr(
+      'imgs/b@3x.png',
+      '/root',
+      [],
+      null,
+      ['png'],
+      filePath => {
+        checkedPaths.push(filePath);
+        return true;
+      },
+    );
+
+    expect(result).toBe('b2 image');
+    expect(checkedPaths).toEqual(['/root/imgs/b@2x.png']);
+  });
 });
 
 describe('getAssetData', () => {