[pigeon] fix swift nsnull casting crash (flutter#3545)

fixes flutter#123387 by forcing NSNull
to nil
also simplifies Int casting, since it was overly complex

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [relevant style guides] and ran the
auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages
repo does use `dart format`.)
- [x] I signed the [CLA].
- [x] The title of the PR starts with the name of the package surrounded
by square brackets, e.g. `[shared_preferences]`
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated `pubspec.yaml` with an appropriate new version according
to the [pub versioning philosophy], or this PR is [exempt from version
changes].
- [x] I updated `CHANGELOG.md` to add a description of the change,
[following repository CHANGELOG style].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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[Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene
[relevant style guides]:
https://github.com/flutter/packages/blob/main/CONTRIBUTING.md#style
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[following repository CHANGELOG style]:
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[test-exempt]:
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Author: tarrinneal

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 9.2.1
+
+* [swift] Fixes NSNull casting crash.
+
 ## 9.2.0
 
 * [cpp] Removes experimental tags.

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 = '9.2.0';
+const String pigeonVersion = '9.2.1';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/lib/swift_generator.dart

@@ -75,9 +75,7 @@ import Flutter
 import FlutterMacOS
 #else
 #error("Unsupported platform.")
-#endif
-''');
-    indent.newln();
+#endif''');
   }
 
   @override
@@ -176,44 +174,17 @@ import FlutterMacOS
     indent.addScoped('{', '}', () {
       enumerate(getFieldsInSerializationOrder(klass),
           (int index, final NamedType field) {
-        final HostDatatype hostDatatype = _getHostDatatype(root, field);
-
         final String listValue = 'list[$index]';
-        final String fieldType = _swiftTypeForDartType(field.type);
 
-        if (field.type.isNullable) {
-          if (!hostDatatype.isBuiltin &&
-              customClassNames.contains(field.type.baseName)) {
-            indent.writeln('var ${field.name}: $fieldType? = nil');
-            indent.write('if let ${field.name}List = $listValue as! [Any]? ');
-            indent.addScoped('{', '}', () {
-              indent.writeln(
-                  '${field.name} = $fieldType.fromList(${field.name}List as [Any])');
-            });
-          } else if (!hostDatatype.isBuiltin &&
-              customEnumNames.contains(field.type.baseName)) {
-            indent.writeln('var ${field.name}: $fieldType? = nil');
-            indent.write('if let ${field.name}RawValue = $listValue as! Int? ');
-            indent.addScoped('{', '}', () {
-              indent.writeln(
-                  '${field.name} = $fieldType(rawValue: ${field.name}RawValue)');
-            });
-          } else {
-            indent.writeln('let ${field.name} = $listValue as! $fieldType? ');
-          }
-        } else {
-          if (!hostDatatype.isBuiltin &&
-              customClassNames.contains(field.type.baseName)) {
-            indent.writeln(
-                'let ${field.name} = $fieldType.fromList($listValue as! [Any])!');
-          } else if (!hostDatatype.isBuiltin &&
-              customEnumNames.contains(field.type.baseName)) {
-            indent.writeln(
-                'let ${field.name} = $fieldType(rawValue: $listValue as! Int)!');
-          } else {
-            indent.writeln('let ${field.name} = $listValue as! $fieldType');
-          }
-        }
+        _writeDecodeCasting(
+          root: root,
+          indent: indent,
+          value: listValue,
+          variableName: field.name,
+          type: field.type,
+          listEncodedClassNames: customClassNames,
+          listEncodedEnumNames: customEnumNames,
+        );
       });
 
       indent.newln();
@@ -345,8 +316,13 @@ import FlutterMacOS
             });
           } else {
             indent.addScoped('{ response in', '}', () {
-              indent.writeln(
-                  'let result = ${_castForceUnwrap("response", func.returnType, root)}');
+              _writeDecodeCasting(
+                root: root,
+                indent: indent,
+                value: 'response',
+                variableName: 'result',
+                type: func.returnType,
+              );
               indent.writeln('completion(result)');
             });
           }
@@ -461,9 +437,13 @@ import FlutterMacOS
                   final String argName =
                       _getSafeArgumentName(index, arg.namedType);
                   final String argIndex = 'args[$index]';
-                  indent.writeln(
-                      'let $argName = ${_castForceUnwrap(argIndex, arg.type, root)}');
-
+                  _writeDecodeCasting(
+                    root: root,
+                    indent: indent,
+                    value: argIndex,
+                    variableName: argName,
+                    type: arg.type,
+                  );
                   if (arg.label == '_') {
                     methodArgument.add(argName);
                   } else {
@@ -607,6 +587,79 @@ import FlutterMacOS
     indent.newln();
   }
 
+  /// Writes decode and casting code for any type.
+  ///
+  /// Optional parameters should only be used for class decoding.
+  void _writeDecodeCasting({
+    required Root root,
+    required Indent indent,
+    required String value,
+    required String variableName,
+    required TypeDeclaration type,
+    Set<String>? listEncodedClassNames,
+    Set<String>? listEncodedEnumNames,
+  }) {
+    String castForceUnwrap(String value, TypeDeclaration type, Root root) {
+      if (isEnum(root, type)) {
+        assert(!type.isNullable,
+            'nullable enums require special code that this helper does not supply');
+        return '${_swiftTypeForDartType(type)}(rawValue: $value as! Int)!';
+      } else if (type.baseName == 'Object') {
+        // Special-cased to avoid warnings about using 'as' with Any.
+        return value;
+      } else if (type.baseName == 'int') {
+        if (type.isNullable) {
+          // Nullable ints need to check for NSNull, and Int32 before casting can be done safely.
+          // This nested ternary is a necessary evil to avoid less efficient conversions.
+          return '$value is NSNull ? nil : ($value is Int64? ? $value as! Int64? : Int64($value as! Int32))';
+        } else {
+          return '$value is Int64 ? $value as! Int64 : Int64($value as! Int32)';
+        }
+      } else if (type.isNullable) {
+        return 'nilOrValue($value)';
+      } else {
+        return '$value as! ${_swiftTypeForDartType(type)}';
+      }
+    }
+
+    final String fieldType = _swiftTypeForDartType(type);
+
+    if (type.isNullable) {
+      if (listEncodedClassNames != null &&
+          listEncodedClassNames.contains(type.baseName)) {
+        indent.writeln('var $variableName: $fieldType? = nil');
+        indent.write('if let ${variableName}List = $value as! [Any]? ');
+        indent.addScoped('{', '}', () {
+          indent.writeln(
+              '$variableName = $fieldType.fromList(${variableName}List)');
+        });
+      } else if (listEncodedEnumNames != null &&
+          listEncodedEnumNames.contains(type.baseName)) {
+        indent.writeln('var $variableName: $fieldType? = nil');
+        indent.writeln(
+            'let ${variableName}EnumVal: Int? = ${castForceUnwrap(value, const TypeDeclaration(baseName: 'Int', isNullable: true), root)}');
+        indent
+            .write('if let ${variableName}RawValue = ${variableName}EnumVal ');
+        indent.addScoped('{', '}', () {
+          indent.writeln(
+              '$variableName = $fieldType(rawValue: ${variableName}RawValue)!');
+        });
+      } else {
+        indent.writeln(
+            'let $variableName: $fieldType? = ${castForceUnwrap(value, type, root)}');
+      }
+    } else {
+      if (listEncodedClassNames != null &&
+          listEncodedClassNames.contains(type.baseName)) {
+        indent.writeln(
+            'let $variableName = $fieldType.fromList($value as! [Any])!');
+      } else {
+        indent.writeln(
+            'let $variableName = ${castForceUnwrap(value, type, root)}');
+      }
+    }
+  }
+
   void _writeWrapResult(Indent indent) {
     indent.newln();
     indent.write('private func wrapResult(_ result: Any?) -> [Any?] ');
@@ -637,11 +690,21 @@ import FlutterMacOS
     });
   }
 
+  void _writeNilOrValue(Indent indent) {
+    indent.format('''
+
+private func nilOrValue<T>(_ value: Any?) -> T? {
+  if value is NSNull { return nil }
+  return (value as Any) as! T?
+}''');
+  }
+
   @override
   void writeGeneralUtilities(
       SwiftOptions generatorOptions, Root root, Indent indent) {
     _writeWrapResult(indent);
     _writeWrapError(indent);
+    _writeNilOrValue(indent);
   }
 }
 
@@ -667,23 +730,6 @@ String _camelCase(String text) {
   return pascal[0].toLowerCase() + pascal.substring(1);
 }
 
-String _castForceUnwrap(String value, TypeDeclaration type, Root root) {
-  final String forceUnwrap = type.isNullable ? '' : '!';
-  final String castUnwrap = type.isNullable ? '?' : '';
-  if (isEnum(root, type)) {
-    final String nullableConditionPrefix =
-        type.isNullable ? '$value == nil ? nil : ' : '';
-    return '$nullableConditionPrefix${_swiftTypeForDartType(type)}(rawValue: $value as! Int)$forceUnwrap';
-  } else if (type.baseName == 'Object') {
-    // Special-cased to avoid warnings about using 'as' with Any.
-    return value;
-  } else if (type.baseName == 'int') {
-    return '($value is Int) ? Int64($value as! Int) : $value as! Int64$castUnwrap';
-  } else {
-    return '$value as! ${_swiftTypeForDartType(type)}$castUnwrap';
-  }
-}
-
 /// Converts a [List] of [TypeDeclaration]s to a comma separated [String] to be
 /// used in Swift code.
 String _flattenTypeArguments(List<TypeDeclaration> args) {

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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), 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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), 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/platform_tests/alternate_language_test_plugin/android/src/main/java/com/example/alternate_language_test_plugin/CoreTests.java

@@ -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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 package com.example.alternate_language_test_plugin;

packages/pigeon/platform_tests/alternate_language_test_plugin/ios/Classes/CoreTests.gen.h

@@ -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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #import <Foundation/Foundation.h>

packages/pigeon/platform_tests/alternate_language_test_plugin/ios/Classes/CoreTests.gen.m

@@ -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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #import "CoreTests.gen.h"

packages/pigeon/platform_tests/flutter_null_safe_unit_tests/lib/core_tests.gen.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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), 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/platform_tests/flutter_null_safe_unit_tests/lib/flutter_unittests.gen.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 (v9.2.0), do not edit directly.
+// Autogenerated from Pigeon (v9.2.1), 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