Always consider @RegisterRestClient interface as REST Clients

extensions/resteasy-classic/resteasy-client/deployment/src/main/java/io/quarkus/restclient/deployment/RestClientProcessor.java

@@ -209,8 +209,10 @@ void processInterfaces(
 
         IndexView index = CompositeIndex.create(beanArchiveIndexBuildItem.getIndex(), combinedIndexBuildItem.getIndex());
 
-        findInterfaces(index, interfaces, returnTypes, REGISTER_REST_CLIENT);
-        findInterfaces(index, interfaces, returnTypes, PATH);
+        findInterfaces(index, interfaces, returnTypes, REGISTER_REST_CLIENT, classInfo -> true);
+        // in there, we are overly cautious it could be an interface for a server class
+        findInterfaces(index, interfaces, returnTypes, PATH,
+                classInfo -> index.getAllKnownImplementors(classInfo.name()).isEmpty());
 
         if (interfaces.isEmpty()) {
             return;
@@ -380,7 +382,7 @@ private static boolean isDefault(short flags) {
     }
 
     private void findInterfaces(IndexView index, Map<DotName, ClassInfo> interfaces, Set<Type> returnTypes,
-            DotName annotationToFind) {
+            DotName annotationToFind, Predicate<ClassInfo> additionalConstraints) {
         for (AnnotationInstance annotation : index.getAnnotations(annotationToFind)) {
             AnnotationTarget target = annotation.target();
             ClassInfo theInfo;
@@ -392,7 +394,7 @@ private void findInterfaces(IndexView index, Map<DotName, ClassInfo> interfaces,
                 continue;
             }
 
-            if (!isRestClientInterface(index, theInfo)) {
+            if (!Modifier.isInterface(theInfo.flags()) || !additionalConstraints.test(theInfo)) {
                 continue;
             }
 
@@ -611,12 +613,6 @@ void unremovableInterceptors(List<RestClientBuildItem> restClientInterfaces, Bea
         if (!unremovableInterceptors.isEmpty()) {
             unremovableBeans.produce(UnremovableBeanBuildItem.beanClassNames(unremovableInterceptors));
         }
-
-    }
-
-    private boolean isRestClientInterface(IndexView index, ClassInfo classInfo) {
-        return Modifier.isInterface(classInfo.flags())
-                && index.getAllKnownImplementors(classInfo.name()).isEmpty();
     }
 
     private static BuiltinScope builtinScopeFromName(DotName scopeName) {

extensions/resteasy-classic/resteasy-client/deployment/src/test/java/io/quarkus/restclient/basic/ClientWithImplementationsInvalidTest.java

@@ -0,0 +1,52 @@
+package io.quarkus.restclient.basic;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import jakarta.enterprise.inject.UnsatisfiedResolutionException;
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+
+import org.eclipse.microprofile.rest.client.inject.RestClient;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+
+public class ClientWithImplementationsInvalidTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .withApplicationRoot((jar) -> jar
+                    .addClasses(MyClient.class, MyImplementation.class))
+            .withConfigurationResource("client-with-implementations.properties")
+            .assertException(t -> {
+                assertThat(t).hasCauseInstanceOf(UnsatisfiedResolutionException.class);
+            });
+
+    @RestClient
+    MyClient client;
+
+    @Test
+    public void testClientBeanHasBeenCreated() {
+        Assertions.assertEquals("hello", client.get());
+    }
+
+    @Path("/client")
+    public interface MyClient {
+
+        @GET
+        @Path("/")
+        String get();
+    }
+
+    public static class MyImplementation implements MyClient {
+
+        @GET
+        @Path("/")
+        @Override
+        public String get() {
+            return "hello";
+        }
+    }
+}

extensions/resteasy-classic/resteasy-client/deployment/src/test/java/io/quarkus/restclient/basic/ClientWithImplementationsTest.java

@@ -0,0 +1,48 @@
+package io.quarkus.restclient.basic;
+
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+
+import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
+import org.eclipse.microprofile.rest.client.inject.RestClient;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+
+public class ClientWithImplementationsTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .withApplicationRoot((jar) -> jar
+                    .addClasses(MyClient.class, MyImplementation.class))
+            .withConfigurationResource("client-with-implementations.properties");
+
+    @RestClient
+    MyClient client;
+
+    @Test
+    public void testClientBeanHasBeenCreated() {
+        Assertions.assertEquals("hello", client.get());
+    }
+
+    @Path("/client")
+    @RegisterRestClient(configKey = "my-client")
+    public interface MyClient {
+
+        @GET
+        @Path("/")
+        String get();
+    }
+
+    public static class MyImplementation implements MyClient {
+
+        @GET
+        @Path("/")
+        @Override
+        public String get() {
+            return "hello";
+        }
+    }
+}

extensions/resteasy-classic/resteasy-client/deployment/src/test/resources/client-with-implementations.properties

@@ -0,0 +1 @@
+quarkus.rest-client.my-client.url=http://localhost:${quarkus.http.test-port:8081}