Make subresource handling for interfaces more nuanced

We don't want to create subresources for interfaces
that are used by multiple resource classes
for the purpose of reusing resource methods
and JAX-RS annotations

Fixes: quarkusio#34657

extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/main/java/io/quarkus/resteasy/reactive/server/deployment/ResteasyReactiveProcessor.java

@@ -683,6 +683,7 @@ public Supplier<Boolean> apply(ClassInfo classInfo) {
                 }
             }
             Map<DotName, ClassInfo> possibleSubResources = new HashMap<>();
+            Set<String> resourceClassNames = null;
             while (!toScan.isEmpty()) {
                 ClassInfo classInfo = toScan.poll();
                 if (scannedResources.containsKey(classInfo.name()) ||
@@ -691,6 +692,25 @@ public Supplier<Boolean> apply(ClassInfo classInfo) {
                     continue;
                 }
                 possibleSubResources.put(classInfo.name(), classInfo);
+
+                if (classInfo.isInterface()) {
+                    int resourceClassImplCount = 0;
+                    if (resourceClassNames == null) {
+                        resourceClassNames = resourceClasses.stream().map(ResourceClass::getClassName)
+                                .collect(Collectors.toSet());
+                    }
+                    for (ClassInfo impl : index.getAllKnownImplementors(classInfo.name())) {
+                        if (resourceClassNames.contains(impl.name().toString())) {
+                            resourceClassImplCount++;
+                        }
+                    }
+                    if (resourceClassImplCount > 1) {
+                        // this is the case were an interface doesn't denote a subresource, but it's simply used
+                        // to share method and annotations between Resource classes
+                        continue;
+                    }
+                }
+
                 Optional<ResourceClass> endpoints = serverEndpointIndexer.createEndpoints(classInfo, false);
                 if (endpoints.isPresent()) {
                     subResourceClasses.add(endpoints.get());

extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/resource/basic/MultipleResourceImplementInterfaceTest.java

@@ -0,0 +1,80 @@
+package io.quarkus.resteasy.reactive.server.test.resource.basic;
+
+import static io.restassured.RestAssured.when;
+import static org.hamcrest.CoreMatchers.is;
+
+import java.util.function.Supplier;
+
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+
+import org.jboss.resteasy.reactive.RestPath;
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+
+public class MultipleResourceImplementInterfaceTest {
+
+    @RegisterExtension
+    static QuarkusUnitTest testExtension = new QuarkusUnitTest()
+            .setArchiveProducer(new Supplier<>() {
+                @Override
+                public JavaArchive get() {
+                    JavaArchive war = ShrinkWrap.create(JavaArchive.class);
+                    war.addClass(HelloResource.class);
+                    war.addClass(Hello2Resource.class);
+                    war.addClass(Shared.class);
+                    return war;
+                }
+            });
+
+    @Test
+    public void hello() {
+        when().get("/hello")
+                .then().statusCode(200).body(is("hello"));
+
+        when().get("/hello/shared/1")
+                .then().statusCode(200).body(is("1"));
+    }
+
+    @Test
+    public void hello2() {
+        when().get("/hello2")
+                .then().statusCode(200).body(is("hello2"));
+
+        when().get("/hello2/shared/h2")
+                .then().statusCode(200).body(is("h2"));
+    }
+
+    @Path("/hello")
+    public static class HelloResource implements Shared {
+
+        @GET
+        public String hello() {
+            return "hello";
+        }
+
+    }
+
+    @Path("/hello2")
+    public static class Hello2Resource implements Shared {
+
+        @GET
+        public String hello() {
+            return "hello2";
+        }
+
+    }
+
+    public interface Shared {
+
+        @GET
+        @Path("/shared/{id}")
+        default String version(@RestPath String id) {
+            return id;
+        }
+    }
+}