if there is no .ios or ios sub-project, don't attempt building for iOS (#31406)

packages/flutter_tools/lib/src/application_package.dart

@@ -306,8 +306,13 @@ abstract class IOSApp extends ApplicationPackage {
   }
 
   factory IOSApp.fromIosProject(IosProject project) {
-    if (getCurrentHostPlatform() != HostPlatform.darwin_x64)
+    if (getCurrentHostPlatform() != HostPlatform.darwin_x64) {
       return null;
+    }
+    // TODO(jonahwilliams): do more verification in this check.
+    if (!project.exists) {
+      return null;
+    }
     return BuildableIOSApp(project);
   }
 

packages/flutter_tools/lib/src/project.dart

@@ -231,6 +231,9 @@ class IosProject {
   /// True, if the parent Flutter project is a module project.
   bool get isModule => parent.isModule;
 
+  /// Whether the flutter application has an iOS project.
+  bool get exists => hostAppRoot.existsSync();
+
   /// The xcode config file for [mode].
   File xcodeConfigFor(String mode) => _flutterLibRoot.childDirectory('Flutter').childFile('$mode.xcconfig');
 

packages/flutter_tools/test/application_package_test.dart

@@ -277,6 +277,14 @@ void main() {
       expect(iosApp.id, 'fooBundleId');
       expect(iosApp.bundleName, 'bundle.app');
     }, overrides: overrides);
+
+    testUsingContext('returns null when there is no ios or .ios directory', () async {
+      fs.file('pubspec.yaml').createSync();
+      fs.file('.packages').createSync();
+      final BuildableIOSApp iosApp = IOSApp.fromIosProject((await FlutterProject.fromDirectory(fs.currentDirectory)).ios);
+
+      expect(iosApp, null);
+    }, overrides: overrides);
   });
 }