[pigeon]fix a crash when casting NSNull to an Array (#4289)

Fixes a crash introduced in #3658: 

```
static func fromList(_ list: [Any?]) -> NativeAuthSession? {
  if let userPoolTokensList = list[2] as! [Any?]? {}
}
```
where `list[2]` is `NSNull`, which is not an Optional, hence can't be casted to `[Any?]?`. 

Recall that `nilOrValue` helper is created for this purpose. So the fix is simply: 

```
static func fromList(_ list: [Any?]) -> NativeAuthSession? {
  if let userPoolTokensList: [Any?] = nilOrValue(list[2]) {} // <- HERE
}
```

## Why didn't we catch this regression

Missing unit tests - we did not test `NSNull` fields to ensure `nilOrValue` works for them.  

## Why did it work in previous version? 

It's surprising that this worked fine before! The original code is: 
```
static func fromList(_ list: [Any]) -> NativeAuthSession? {
  if let userPoolTokensList = list[2] as! [Any]? {}
}
```
From [my previous PR](flutter/flutter#129283), we know that list[2] is an implicit optional (that contains a NSNull value). I think Swift made an exception here when casting implicit optional NSNull (either intentionally or unintentionally). 

*List which issues are fixed by this PR. You must list at least one issue.*

Fixes flutter/flutter#129283

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

Author: hellohuanlin

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 10.1.2
+
+* [swift] Fixes a crash when passing `null` for nested nullable classes. 
+
 ## 10.1.1
 
 * Updates README to better reflect modern usage.

packages/pigeon/example/app/android/app/src/main/java/io/flutter/plugins/Messages.java

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 import android.util.Log;

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 

packages/pigeon/example/app/ios/Runner/Messages.g.swift

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 import Foundation

packages/pigeon/example/app/lib/src/messages.g.dart

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, prefer_null_aware_operators, omit_local_variable_types, unused_shown_name, unnecessary_import
 

packages/pigeon/example/app/macos/Runner/messages.g.h

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #import <Foundation/Foundation.h>

packages/pigeon/example/app/macos/Runner/messages.g.m

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #import "messages.g.h"

packages/pigeon/example/app/windows/runner/messages.g.cpp

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #undef _HAS_EXCEPTIONS

packages/pigeon/example/app/windows/runner/messages.g.h

@@ -1,7 +1,7 @@
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Autogenerated from Pigeon (v10.1.1), do not edit directly.
+// Autogenerated from Pigeon (v10.1.2), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #ifndef PIGEON_MESSAGES_G_H_

packages/pigeon/lib/generator_tools.dart

@@ -11,7 +11,7 @@ import 'ast.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '10.1.1';
+const String pigeonVersion = '10.1.2';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/lib/swift_generator.dart

@@ -627,7 +627,8 @@ import FlutterMacOS
       if (listEncodedClassNames != null &&
           listEncodedClassNames.contains(type.baseName)) {
         indent.writeln('var $variableName: $fieldType? = nil');
-        indent.write('if let ${variableName}List = $value as! [Any?]? ');
+        indent
+            .write('if let ${variableName}List: [Any?] = nilOrValue($value) ');
         indent.addScoped('{', '}', () {
           indent.writeln(
               '$variableName = $fieldType.fromList(${variableName}List)');

packages/pigeon/mock_handler_tester/test/message.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v9.2.5), do not edit directly.
+// Autogenerated from Pigeon (v10.1.1), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, prefer_null_aware_operators, omit_local_variable_types, unused_shown_name, unnecessary_import
 

packages/pigeon/mock_handler_tester/test/test.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v9.2.5), do not edit directly.
+// Autogenerated from Pigeon (v10.1.1), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, unnecessary_import
 // ignore_for_file: avoid_relative_lib_imports

packages/pigeon/pigeons/core_tests.dart

@@ -10,7 +10,7 @@ enum AnEnum {
   three,
 }
 
-// A class containing all supported types.
+/// A class containing all supported types.
 class AllTypes {
   AllTypes({
     this.aBool = false,
@@ -43,7 +43,7 @@ class AllTypes {
   String aString;
 }
 
-// A class containing all supported nullable types.
+/// A class containing all supported nullable types.
 class AllNullableTypes {
   AllNullableTypes(
     this.aNullableBool,
@@ -82,10 +82,15 @@ class AllNullableTypes {
   String? aNullableString;
 }
 
-// A class for testing nested object handling.
-class AllNullableTypesWrapper {
-  AllNullableTypesWrapper(this.values);
-  AllNullableTypes values;
+/// A class for testing nested class handling.
+///
+/// This is needed to test nested nullable and non-nullable classes,
+/// `AllNullableTypes` is non-nullable here as it is easier to instantiate
+/// than `AllTypes` when testing doesn't require both (ie. testing null classes).
+class AllClassesWrapper {
+  AllClassesWrapper(this.allNullableTypes, this.allTypes);
+  AllNullableTypes allNullableTypes;
+  AllTypes? allTypes;
 }
 
 /// The core interface that each host language plugin must implement in
@@ -152,6 +157,11 @@ abstract class HostIntegrationCoreApi {
   @SwiftFunction('echo(_:)')
   Map<String?, Object?> echoMap(Map<String?, Object?> aMap);
 
+  /// Returns the passed map to test nested class serialization and deserialization.
+  @ObjCSelector('echoClassWrapper:')
+  @SwiftFunction('echo(_:)')
+  AllClassesWrapper echoClassWrapper(AllClassesWrapper wrapper);
+
   // ========== Synchronous nullable method tests ==========
 
   /// Returns the passed object, to test serialization and deserialization.
@@ -163,13 +173,13 @@ abstract class HostIntegrationCoreApi {
   /// sending of nested objects.
   @ObjCSelector('extractNestedNullableStringFrom:')
   @SwiftFunction('extractNestedNullableString(from:)')
-  String? extractNestedNullableString(AllNullableTypesWrapper wrapper);
+  String? extractNestedNullableString(AllClassesWrapper wrapper);
 
   /// Returns the inner `aString` value from the wrapped object, to test
   /// sending of nested objects.
   @ObjCSelector('createNestedObjectWithNullableString:')
   @SwiftFunction('createNestedObject(with:)')
-  AllNullableTypesWrapper createNestedNullableString(String? nullableString);
+  AllClassesWrapper createNestedNullableString(String? nullableString);
 
   /// Returns passed in arguments of multiple types.
   @ObjCSelector('sendMultipleNullableTypesABool:anInt:aString:')

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/main/java/com/example/alternate_language_test_plugin/AlternateLanguageTestPlugin.java

@@ -6,8 +6,8 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import com.example.alternate_language_test_plugin.CoreTests.AllClassesWrapper;
 import com.example.alternate_language_test_plugin.CoreTests.AllNullableTypes;
-import com.example.alternate_language_test_plugin.CoreTests.AllNullableTypesWrapper;
 import com.example.alternate_language_test_plugin.CoreTests.AllTypes;
 import com.example.alternate_language_test_plugin.CoreTests.FlutterIntegrationCoreApi;
 import com.example.alternate_language_test_plugin.CoreTests.HostIntegrationCoreApi;
@@ -99,17 +99,21 @@ public void throwErrorFromVoid() {
     return aMap;
   }
 
+  @NonNull
+  public AllClassesWrapper echoClassWrapper(@NonNull AllClassesWrapper wrapper) {
+    return wrapper;
+  }
+
   @Override
-  public @Nullable String extractNestedNullableString(@NonNull AllNullableTypesWrapper wrapper) {
-    return wrapper.getValues().getANullableString();
+  public @Nullable String extractNestedNullableString(@NonNull AllClassesWrapper wrapper) {
+    return wrapper.getAllNullableTypes().getANullableString();
   }
 
   @Override
-  public @NonNull AllNullableTypesWrapper createNestedNullableString(
-      @Nullable String nullableString) {
+  public @NonNull AllClassesWrapper createNestedNullableString(@Nullable String nullableString) {
     AllNullableTypes innerObject =
         new AllNullableTypes.Builder().setANullableString(nullableString).build();
-    return new AllNullableTypesWrapper.Builder().setValues(innerObject).build();
+    return new AllClassesWrapper.Builder().setAllNullableTypes(innerObject).build();
   }
 
   @Override