Enable and fix warnings

packages/pigeon/lib/java_generator.dart

@@ -458,7 +458,7 @@ class JavaGenerator extends StructuredGenerator<JavaOptions> {
                       '$returnType $output = channelReply == null ? null : ((Number) channelReply).longValue();');
                 } else {
                   indent.writeln(
-                      '$returnType $output = ($returnType) channelReply;');
+                      '$returnType $output = ${_cast('channelReply', javaType: returnType)};');
                 }
                 indent.writeln('callback.reply($output);');
               });
@@ -627,8 +627,8 @@ class JavaGenerator extends StructuredGenerator<JavaOptions> {
                   String accessor = 'args.get($index)';
                   if (isEnum(root, arg.type)) {
                     accessor = _intToEnum(accessor, arg.type.baseName);
-                  } else if (argType != 'Object') {
-                    accessor = '($argType) $accessor';
+                  } else {
+                    accessor = _cast(accessor, javaType: argType);
                   }
                   indent.writeln('$argType $argName = $accessor;');
                   if (!arg.type.isNullable) {
@@ -646,7 +646,7 @@ class JavaGenerator extends StructuredGenerator<JavaOptions> {
                     method.returnType.isVoid ? 'null' : 'result';
                 const String resultName = 'resultCallback';
                 indent.format('''
-Result<$returnType> $resultName = 
+Result<$returnType> $resultName =
 \t\tnew Result<$returnType>() {
 \t\t\tpublic void success($returnType result) {
 \t\t\t\twrapped.add(0, $resultValue);
@@ -871,6 +871,13 @@ String _nullsafeJavaTypeForDartType(TypeDeclaration type) {
   return '$nullSafe${_javaTypeForDartType(type)}';
 }
 
+/// Returns an expression to cast [variable] to [javaType].
+String _cast(String variable, {required String javaType}) {
+  // Special-case Object, since casting to Object doesn't do anything, and
+  // causes a warning.
+  return javaType == 'Object' ? variable : '($javaType) $variable';
+}
+
 /// Casts variable named [varName] to the correct host datatype for [field].
 /// This is for use in codecs where we may have a map representation of an
 /// object.
@@ -884,6 +891,6 @@ String _castObject(
       classes.map((Class x) => x.name).contains(field.type.baseName)) {
     return '($varName == null) ? null : ${hostDatatype.datatype}.fromList((ArrayList<Object>) $varName)';
   } else {
-    return '(${hostDatatype.datatype}) $varName';
+    return _cast(varName, javaType: hostDatatype.datatype);
   }
 }

packages/pigeon/lib/kotlin_generator.dart

@@ -180,12 +180,13 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
           final HostDatatype hostDatatype = _getHostDatatype(root, field);
           String toWriteValue = '';
           final String fieldName = field.name;
+          final String safeCall = field.type.isNullable ? '?' : '';
           if (!hostDatatype.isBuiltin &&
               customClassNames.contains(field.type.baseName)) {
-            toWriteValue = '$fieldName?.toList()';
+            toWriteValue = '$fieldName$safeCall.toList()';
           } else if (!hostDatatype.isBuiltin &&
               customEnumNames.contains(field.type.baseName)) {
-            toWriteValue = '$fieldName?.raw';
+            toWriteValue = '$fieldName$safeCall.raw';
           } else {
             toWriteValue = fieldName;
           }
@@ -244,7 +245,8 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
               indent.addln(
                   '.let { if (it is Int) it.toLong() else it as? Long }');
             } else {
-              indent.writeln('val ${field.name} = $listValue as? $fieldType');
+              indent.writeln(
+                  'val ${field.name} = ${_cast(listValue, kotlinType: fieldType, safeCast: true)}');
             }
           } else {
             if (!hostDatatype.isBuiltin &&
@@ -260,7 +262,8 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
               indent
                   .addln('.let { if (it is Int) it.toLong() else it as Long }');
             } else {
-              indent.writeln('val ${field.name} = $listValue as $fieldType');
+              indent.writeln(
+                  'val ${field.name} = ${_cast(listValue, kotlinType: fieldType)}');
             }
           }
         });
@@ -380,13 +383,15 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
               indent.writeln('callback()');
             });
           } else {
-            final String forceUnwrap = func.returnType.isNullable ? '?' : '';
             indent.addScoped('{', '}', () {
               if (func.returnType.baseName == 'int') {
+                final String forceUnwrap =
+                    func.returnType.isNullable ? '?' : '';
                 indent.writeln(
                     'val result = if (it is Int) it.toLong() else it as$forceUnwrap Long');
               } else {
-                indent.writeln('val result = it as$forceUnwrap $returnType');
+                indent.writeln(
+                    'val result = ${_cast('it', kotlinType: returnType, safeCast: func.returnType.isNullable)}');
               }
               indent.writeln('callback(result)');
             });
@@ -507,7 +512,6 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
 
                 indent.write('channel.setMessageHandler ');
                 indent.addScoped('{ $messageVarName, reply ->', '}', () {
-                  indent.writeln('var wrapped = listOf<Any?>()');
                   final List<String> methodArguments = <String>[];
                   if (method.arguments.isNotEmpty) {
                     indent.writeln('val args = message as List<Any?>');
@@ -543,6 +547,7 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
                       });
                     });
                   } else {
+                    indent.writeln('var wrapped: List<Any?>');
                     indent.write('try ');
                     indent.addScoped('{', '}', () {
                       if (method.returnType.isVoid) {
@@ -669,15 +674,15 @@ String _castForceUnwrap(String value, TypeDeclaration type, Root root) {
         type.isNullable ? '$value == null ? null : ' : '';
     return '$nullableConditionPrefix${_kotlinTypeForDartType(type)}.ofRaw($value as Int)$forceUnwrap';
   } else {
-    final String castUnwrap = type.isNullable ? '?' : '';
-
     // The StandardMessageCodec can give us [Integer, Long] for
     // a Dart 'int'.  To keep things simple we just use 64bit
     // longs in Pigeon with Kotlin.
     if (type.baseName == 'int') {
+      final String castUnwrap = type.isNullable ? '?' : '';
       return '$value.let { if (it is Int) it.toLong() else it as$castUnwrap Long }';
     } else {
-      return '$value as$castUnwrap ${_kotlinTypeForDartType(type)}';
+      return _cast(value,
+          kotlinType: _kotlinTypeForDartType(type), safeCast: type.isNullable);
     }
   }
 }
@@ -741,3 +746,13 @@ String _nullsafeKotlinTypeForDartType(TypeDeclaration type) {
   final String nullSafe = type.isNullable ? '?' : '';
   return '${_kotlinTypeForDartType(type)}$nullSafe';
 }
+
+/// Returns an expression to cast [variable] to [kotlinType].
+String _cast(String variable,
+    {required String kotlinType, bool safeCast = false}) {
+  // Special-case Any, since no-op casts cause warnings.
+  if (kotlinType == 'Any?' || (safeCast && kotlinType == 'Any')) {
+    return variable;
+  }
+  return '$variable as${safeCast ? '?' : ''} $kotlinType';
+}

packages/pigeon/platform_tests/alternate_language_test_plugin/android/build.gradle

@@ -50,3 +50,7 @@ android {
         testImplementation "org.mockito:mockito-core:5.+"
     }
 }
+
+project.getTasks().withType(JavaCompile){
+    options.compilerArgs.addAll(["-Xlint:all", "-Werror"])
+}

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

@@ -3239,7 +3239,7 @@ public void throwError(Reply<Object> callback) {
           null,
           channelReply -> {
             @SuppressWarnings("ConstantConditions")
-            Object output = (Object) channelReply;
+            Object output = channelReply;
             callback.reply(output);
           });
     }

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/AllDatatypesTest.java

@@ -26,6 +26,7 @@ public void nullValues() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
+              @SuppressWarnings("unchecked")
               ArrayList<Object> args =
                   (ArrayList<Object>) FlutterIntegrationCoreApi.getCodec().decodeMessage(message);
               ByteBuffer replyData =
@@ -101,6 +102,7 @@ public void hasValues() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
+              @SuppressWarnings("unchecked")
               ArrayList<Object> args =
                   (ArrayList<Object>) FlutterIntegrationCoreApi.getCodec().decodeMessage(message);
               ByteBuffer replyData =

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/AsyncTest.java

@@ -61,7 +61,7 @@ public void asyncSuccess() {
             (bytes) -> {
               bytes.rewind();
               @SuppressWarnings("unchecked")
-              ArrayList wrapped = (ArrayList) codec.decodeMessage(bytes);
+              ArrayList<Object> wrapped = (ArrayList<Object>) codec.decodeMessage(bytes);
               assertTrue(wrapped.size() == 1);
               didCall[0] = true;
             });
@@ -88,7 +88,7 @@ public void asyncError() {
             (bytes) -> {
               bytes.rewind();
               @SuppressWarnings("unchecked")
-              ArrayList wrapped = (ArrayList) codec.decodeMessage(bytes);
+              ArrayList<Object> wrapped = (ArrayList<Object>) codec.decodeMessage(bytes);
               assertTrue(wrapped.size() > 1);
               assertEquals("java.lang.Exception: error", (String) wrapped.get(0));
               didCall[0] = true;

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/ListTest.java

@@ -28,7 +28,9 @@ public void listInList() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
-              ArrayList args = (ArrayList) FlutterSmallApi.getCodec().decodeMessage(message);
+              @SuppressWarnings("unchecked")
+              ArrayList<Object> args =
+                  (ArrayList<Object>) FlutterSmallApi.getCodec().decodeMessage(message);
               ByteBuffer replyData = FlutterSmallApi.getCodec().encodeMessage(args.get(0));
               replyData.position(0);
               reply.reply(replyData);

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/MultipleArityTest.java

@@ -22,6 +22,7 @@ public void subtract() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
+              @SuppressWarnings("unchecked")
               ArrayList<Object> args =
                   (ArrayList<Object>) MultipleArityFlutterApi.getCodec().decodeMessage(message);
               Long arg0 = (Long) args.get(0);

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/NullableReturnsTest.java

@@ -39,7 +39,7 @@ public void nullArgHostApi() {
             (bytes) -> {
               bytes.rewind();
               @SuppressWarnings("unchecked")
-              ArrayList wrapped = (ArrayList) codec.decodeMessage(bytes);
+              ArrayList<Object> wrapped = (ArrayList<Object>) codec.decodeMessage(bytes);
               assertTrue(wrapped.size() == 1);
             });
   }
@@ -52,8 +52,9 @@ public void nullArgFlutterApi() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
-              ArrayList args =
-                  (ArrayList)
+              @SuppressWarnings("unchecked")
+              ArrayList<Object> args =
+                  (ArrayList<Object>)
                       NullableReturns.NullableArgFlutterApi.getCodec().decodeMessage(message);
               assertNull(args.get(0));
               ByteBuffer replyData =

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/PigeonTest.java

@@ -46,7 +46,7 @@ public void errorMessage() {
             (bytes) -> {
               bytes.rewind();
               @SuppressWarnings("unchecked")
-              ArrayList error = (ArrayList) codec.decodeMessage(bytes);
+              ArrayList<Object> error = (ArrayList<Object>) codec.decodeMessage(bytes);
               assertNotNull(error.get(0));
               assertNotNull(error.get(1));
               String details = (String) error.get(2);

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/test/java/com/example/alternate_language_test_plugin/PrimitiveTest.java

@@ -28,7 +28,9 @@ private static BinaryMessenger makeMockBinaryMessenger() {
               ByteBuffer message = invocation.getArgument(1);
               BinaryMessenger.BinaryReply reply = invocation.getArgument(2);
               message.position(0);
-              ArrayList args = (ArrayList) PrimitiveFlutterApi.getCodec().decodeMessage(message);
+              @SuppressWarnings("unchecked")
+              ArrayList<Object> args =
+                  (ArrayList<Object>) PrimitiveFlutterApi.getCodec().decodeMessage(message);
               Object arg = args.get(0);
               if (arg instanceof Long) {
                 Long longArg = (Long) arg;
@@ -88,7 +90,7 @@ public void primitiveIntHostApi() {
         .setMessageHandler(eq("dev.flutter.pigeon.PrimitiveHostApi.anInt"), handler.capture());
     MessageCodec<Object> codec = PrimitiveHostApi.getCodec();
     @SuppressWarnings("unchecked")
-    ByteBuffer message = codec.encodeMessage(new ArrayList(Arrays.asList((Integer) 1)));
+    ByteBuffer message = codec.encodeMessage(new ArrayList<Object>(Arrays.asList((Integer) 1)));
     message.rewind();
     handler
         .getValue()
@@ -97,7 +99,7 @@ public void primitiveIntHostApi() {
             (bytes) -> {
               bytes.rewind();
               @SuppressWarnings("unchecked")
-              ArrayList wrapped = (ArrayList) codec.decodeMessage(bytes);
+              ArrayList<Object> wrapped = (ArrayList<Object>) codec.decodeMessage(bytes);
               assertTrue(wrapped.size() > 0);
               assertEquals(1L, ((Long) wrapped.get(0)).longValue());
             });

packages/pigeon/platform_tests/test_plugin/android/build.gradle

@@ -34,6 +34,7 @@ android {
 
     kotlinOptions {
         jvmTarget = '1.8'
+        allWarningsAsErrors = true
     }
 
     sourceSets {