3.x: enable javac parameter saving in class files (#6839)

Author: akarnokd

build.gradle

@@ -87,6 +87,10 @@ dependencies {
     testImplementation "com.google.guava:guava:$guavaVersion"
 }
 
+tasks.withType(JavaCompile) {
+    options.compilerArgs << "-parameters";
+}
+
 javadoc {
     failOnError = false
     exclude "**/internal/**"

src/test/java/io/reactivex/rxjava3/validators/ParameterNamesInClassesTest.java

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is
+ * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
+ * the License for the specific language governing permissions and limitations under the License.
+ */
+
+package io.reactivex.rxjava3.validators;
+
+import static org.junit.Assert.assertEquals;
+import org.junit.Test;
+
+public class ParameterNamesInClassesTest {
+    void method(int paramName) {
+        // deliberately empty
+    }
+
+    @Test
+    public void javacParametersEnabled() throws Exception {
+        assertEquals("Please enable saving parameter names via the -parameters javac argument",
+                "paramName",
+                getClass()
+                .getDeclaredMethod("method", Integer.TYPE)
+                .getParameters()[0].getName());
+    }
+}