Handle generic types for ParamConverter in REST Client

Fixes: quarkusio#36639

extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/main/java/io/quarkus/jaxrs/client/reactive/deployment/JaxrsClientReactiveProcessor.java

@@ -2652,7 +2652,7 @@ private ResultHandle addQueryParam(MethodInfo jandexMethod, BytecodeCreator meth
             if (isCollection(valueType, index)) {
                 if (valueType.kind() == PARAMETERIZED_TYPE) {
                     Type paramType = valueType.asParameterizedType().arguments().get(0);
-                    if (paramType.kind() == CLASS) {
+                    if ((paramType.kind() == CLASS) || (paramType.kind() == PARAMETERIZED_TYPE)) {
                         componentType = paramType.name().toString();
                     }
                 }
@@ -2679,7 +2679,7 @@ private ResultHandle addQueryParam(MethodInfo jandexMethod, BytecodeCreator meth
             } else if (isCollection(type, index)) {
                 if (type.kind() == PARAMETERIZED_TYPE) {
                     Type paramType = type.asParameterizedType().arguments().get(0);
-                    if (paramType.kind() == CLASS) {
+                    if ((paramType.kind() == CLASS) || (paramType.kind() == PARAMETERIZED_TYPE)) {
                         componentType = paramType.name().toString();
                     }
                 }

extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/converter/GenericsConverterTest.java

@@ -0,0 +1,127 @@
+package io.quarkus.rest.client.reactive.converter;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.net.URI;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.QueryParam;
+import jakarta.ws.rs.ext.ParamConverter;
+import jakarta.ws.rs.ext.ParamConverterProvider;
+import jakarta.ws.rs.ext.Provider;
+
+import org.eclipse.microprofile.rest.client.RestClientBuilder;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+import io.quarkus.test.common.http.TestHTTPResource;
+
+public class GenericsConverterTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest TEST = new QuarkusUnitTest();
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @Test
+    void testSingle() {
+        TestClient client = RestClientBuilder.newBuilder().baseUri(baseUri)
+                .build(TestClient.class);
+        var result = client.wrapper(new WrapperClass<>(StatusEnum.ACTIVE));
+        assertEquals("ACTIVE", result);
+    }
+
+    @Test
+    void testList() {
+        TestClient client = RestClientBuilder.newBuilder().baseUri(baseUri)
+                .build(TestClient.class);
+        var result = client
+                .wrapperList(List.of(new WrapperClass<>(StatusEnum.ACTIVE), new WrapperClass<>(StatusEnum.INACTIVE)));
+        assertEquals("ACTIVE,INACTIVE", result);
+    }
+
+    public enum StatusEnum {
+
+        ACTIVE,
+        INACTIVE
+    }
+
+    public static class WrapperClass<E extends Enum<E>> {
+
+        private final E value;
+
+        public WrapperClass(final E value) {
+            this.value = value;
+        }
+
+        public E getValue() {
+            return value;
+        }
+    }
+
+    public static class WrapperClassParamConverter implements ParamConverter<WrapperClass<?>> {
+
+        @Override
+        public WrapperClass<?> fromString(String value) {
+            return new WrapperClass<>(Enum.valueOf(StatusEnum.class, value));
+        }
+
+        @Override
+        public String toString(WrapperClass<?> wrapperClass) {
+            return wrapperClass != null ? wrapperClass.getValue().toString() : null;
+        }
+
+    }
+
+    @Provider
+    public static class WrapperClassParamConverterProvider implements ParamConverterProvider {
+
+        @Override
+        @SuppressWarnings("unchecked")
+        public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {
+            if (WrapperClass.class.isAssignableFrom(rawType)) {
+                return (ParamConverter<T>) new WrapperClassParamConverter();
+            }
+
+            return null;
+        }
+    }
+
+    @Path("/test")
+    public static class TestResource {
+
+        @GET
+        @Path("/single")
+        public String wrapper(@QueryParam("wrapper") final WrapperClass<StatusEnum> wrapper) {
+            return wrapper.getValue().toString();
+        }
+
+        @GET
+        @Path("/list")
+        public String wrapperList(@QueryParam("wrapperList") final List<WrapperClass<StatusEnum>> wrapperList) {
+            return wrapperList.stream().map(WrapperClass::getValue).map(Enum::name).collect(Collectors.joining(","));
+        }
+
+    }
+
+    @Path("/test")
+    public interface TestClient {
+
+        @GET
+        @Path("/single")
+        String wrapper(@QueryParam("wrapper") final WrapperClass<StatusEnum> wrapper);
+
+        @GET
+        @Path("/list")
+        String wrapperList(@QueryParam("wrapperList") final List<WrapperClass<StatusEnum>> wrapperList);
+
+    }
+
+}