Take ParamConverterProvider into account for form params in REST Clie…

…nt Reactive

Fixes: quarkusio#23034

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

@@ -50,6 +50,7 @@
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.MultivaluedHashMap;
 import javax.ws.rs.core.MultivaluedMap;
+import javax.ws.rs.ext.ParamConverter;
 import javax.ws.rs.ext.ParamConverterProvider;
 
 import org.apache.http.entity.ContentType;
@@ -131,6 +132,7 @@
 import io.quarkus.deployment.recording.RecorderContext;
 import io.quarkus.deployment.util.JandexUtil;
 import io.quarkus.gizmo.AssignableResultHandle;
+import io.quarkus.gizmo.BranchResult;
 import io.quarkus.gizmo.BytecodeCreator;
 import io.quarkus.gizmo.CatchBlockCreator;
 import io.quarkus.gizmo.ClassCreator;
@@ -898,8 +900,22 @@ A more full example of generated client (with sub-resource) can is at the bottom
                             invocationBuilderEnrichers.put(handleHeaderDescriptor, methodCreator.getMethodParam(paramIdx));
                         } else if (param.parameterType == ParameterType.FORM) {
                             formParams = createIfAbsent(methodCreator, formParams);
-                            methodCreator.invokeInterfaceMethod(MULTIVALUED_MAP_ADD, formParams,
-                                    methodCreator.load(param.name), methodCreator.getMethodParam(paramIdx));
+                            ResultHandle convertedFormParam = methodCreator.invokeVirtualMethod(
+                                    MethodDescriptor.ofMethod(RestClientBase.class, "convertParam", Object.class, Object.class,
+                                            Class.class),
+                                    methodCreator.getThis(), methodCreator.getMethodParam(paramIdx),
+                                    methodCreator.loadClass(param.type));
+                            ResultHandle isString = methodCreator.instanceOf(convertedFormParam, String.class);
+                            BranchResult isStringBranch = methodCreator.ifTrue(isString);
+                            isStringBranch.falseBranch().throwException(IllegalStateException.class,
+                                    "Form parameter '" + param.name
+                                            + "' could not be converted to 'String' for REST Client interface '"
+                                            + restClientInterface.getClassName() + "'. A proper implementation of '"
+                                            + ParamConverter.class.getName() + "' needs to be returned by a '"
+                                            + ParamConverterProvider.class.getName()
+                                            + "' that is registered with the client via the @RegisterProvider annotation on the REST Client interface.");
+                            isStringBranch.trueBranch().invokeInterfaceMethod(MULTIVALUED_MAP_ADD, formParams,
+                                    methodCreator.load(param.name), convertedFormParam);
                         } else if (param.parameterType == ParameterType.MULTI_PART_FORM) {
                             if (multipartForm != null) {
                                 throw new IllegalArgumentException("MultipartForm data set twice for method "

extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/form/FormWithConverterTest.java

@@ -0,0 +1,91 @@
+package io.quarkus.rest.client.reactive.form;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.net.URI;
+
+import javax.ws.rs.Consumes;
+import javax.ws.rs.FormParam;
+import javax.ws.rs.POST;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.ext.ParamConverter;
+import javax.ws.rs.ext.ParamConverterProvider;
+
+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 FormWithConverterTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest TEST = new QuarkusUnitTest()
+            .withApplicationRoot((jar) -> jar
+                    .addClasses(ResourceClient.class, Resource.class, Input.class, InputParamConverterProvider.class));
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @Test
+    void test() {
+        ResourceClient client = RestClientBuilder.newBuilder().baseUri(baseUri).register(InputParamConverterProvider.class)
+                .build(ResourceClient.class);
+        String result = client.hello(new Input("hey"));
+        assertThat(result).isEqualTo("hey!");
+    }
+
+    public interface ResourceClient {
+
+        @POST
+        @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
+        @Produces(MediaType.TEXT_PLAIN)
+        String hello(@FormParam("message") Input input);
+    }
+
+    @Path("")
+    public static class Resource {
+
+        @POST
+        @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
+        @Produces(MediaType.TEXT_PLAIN)
+        public String hello(@FormParam("message") String message) {
+            return message + "!";
+        }
+    }
+
+    public static class Input {
+
+        public String value;
+
+        public Input(String value) {
+            this.value = value;
+        }
+    }
+
+    public static class InputParamConverterProvider implements ParamConverterProvider {
+        @SuppressWarnings("unchecked")
+        @Override
+        public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {
+            if (rawType == Input.class) {
+                return (ParamConverter<T>) new ParamConverter<Input>() {
+                    @Override
+                    public Input fromString(String value) {
+                        return new Input(value);
+                    }
+
+                    @Override
+                    public String toString(Input value) {
+                        return value.value;
+                    }
+                };
+            }
+            return null;
+        }
+    }
+}