fix

packages/flutter_tools/lib/src/asset.dart

@@ -11,6 +11,7 @@ import 'package:standard_message_codec/standard_message_codec.dart';
 import 'base/common.dart';
 import 'base/context.dart';
 import 'base/deferred_component.dart';
+import 'base/error_handling_io.dart';
 import 'base/file_system.dart';
 import 'base/logger.dart';
 import 'base/platform.dart';
@@ -1298,8 +1299,16 @@ class _AssetDirectoryCache {
   List<String> variantsFor(String assetPath) {
     final String directory = _fileSystem.path.dirname(assetPath);
 
-    if (!_fileSystem.directory(directory).existsSync()) {
-      return const <String>[];
+    try {
+      if (!_fileSystem.directory(directory).existsSync()) {
+        return const <String>[];
+      }
+    } on FileSystemException catch (e) {
+      throwToolExit(
+        'Unable to check the existence of asset file "$assetPath". '
+        'Ensure that the asset file is declared is a valid local file system path.\n'
+        'Details: $e',
+      );
     }
 
     if (_cache.containsKey(assetPath)) {

packages/flutter_tools/test/general.shard/asset_bundle_test.dart

@@ -153,7 +153,7 @@ flutter:
       ProcessManager: () => FakeProcessManager.any(),
     });
 
-    testUsingContext('throws ToolExit when directory entry contains invalid characters', () async {
+    testUsingContext('throws ToolExit when directory entry contains invalid characters (Windows only)', () async {
       testFileSystem.file('.packages').createSync();
       testFileSystem.file('pubspec.yaml')
         ..createSync()
@@ -177,6 +177,35 @@ flutter:
       Platform: () => FakePlatform(operatingSystem: 'windows'),
     });
 
+    testUsingContext('throws ToolExit when file entry contains invalid characters (Windows only)', () async {
+      globals.fs.file('.packages').createSync();
+      globals.fs.file('pubspec.yaml')
+        ..createSync()
+        ..writeAsStringSync(r'''
+name: example
+flutter:
+  assets:
+    - http://website.com/hi.png
+''');
+      final AssetBundle bundle = AssetBundleFactory.instance.createBundle();
+      expect(() => bundle.build(packagesPath: '.packages'), throwsToolExit(
+        message: 'Unable to check the existence of asset file ',
+      ));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => MemoryFileSystem(style: FileSystemStyle.windows,
+      opHandle: (String context, FileSystemOp operation) {
+        if (operation == FileSystemOp.exists && context == r'C:\http:\\website.com') {
+          throw const FileSystemException(
+            r"FileSystemException: Exists failed, path = 'C:\http:\\website.com' "
+            '(OS Error: The filename, directory name, or volume label syntax is '
+            'incorrect., errno = 123)',
+          );
+        }
+      },),
+      ProcessManager: () => FakeProcessManager.any(),
+      Platform: () => FakePlatform(operatingSystem: 'windows'),
+    });
+
     testUsingContext('handle removal of wildcard directories', () async {
       globals.fs.file(globals.fs.path.join('assets', 'foo', 'bar.txt')).createSync(recursive: true);
       final File pubspec = globals.fs.file('pubspec.yaml')