Use Set.of() instead of Collections.emptySet() in core parts

Marko told me that it was actually faster to iterate and from what I can
see it's true.
I won't change it everywhere but it seems like a good idea to make the
change in the Core parts.

Note that some of the changes I made might not be critical but it wasn't
worth the hassle to check everywhere if it actually made a noticeable
difference given the size of the change.

Author: gsmet

core/deployment/src/main/java/io/quarkus/deployment/builditem/AdditionalIndexedClassesBuildItem.java

@@ -1,6 +1,5 @@
 package io.quarkus.deployment.builditem;
 
-import java.util.Collections;
 import java.util.Set;
 
 import io.quarkus.builder.item.MultiBuildItem;
@@ -18,7 +17,7 @@ public AdditionalIndexedClassesBuildItem(String... classesToIndex) {
     }
 
     public AdditionalIndexedClassesBuildItem(String classToIndex) {
-        this.classesToIndex = Collections.singleton(classToIndex);
+        this.classesToIndex = Set.of(classToIndex);
     }
 
     public Set<String> getClassesToIndex() {

core/deployment/src/main/java/io/quarkus/deployment/configuration/ConfigMappingUtils.java

@@ -3,7 +3,6 @@
 import static io.smallrye.config.ConfigMappings.ConfigClass.configClass;
 import static org.jboss.jandex.AnnotationTarget.Kind.CLASS;
 
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
@@ -222,7 +221,7 @@ private static Set<Type> collectTypes(CombinedIndexBuildItem combinedIndex, Clas
         DotName configIfaceName = DotName.createSimple(configClass.getName());
         ClassInfo configIfaceInfo = index.getClassByName(configIfaceName);
         if ((configIfaceInfo == null) || configIfaceInfo.interfaceNames().isEmpty()) {
-            return Collections.singleton(Type.create(configIfaceName, Type.Kind.CLASS));
+            return Set.of(Type.create(configIfaceName, Type.Kind.CLASS));
         }
 
         Set<DotName> allIfaces = new HashSet<>();

independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/BeanDeployment.java

@@ -723,17 +723,17 @@ Collection<AnnotationInstance> extractInterceptorBindings(AnnotationInstance ann
     private static Collection<AnnotationInstance> extractAnnotations(AnnotationInstance annotation,
             Map<DotName, ClassInfo> singulars, Map<DotName, ClassInfo> repeatables) {
         if (!annotation.runtimeVisible()) {
-            return Collections.emptyList();
+            return List.of();
         }
         DotName annotationName = annotation.name();
         if (singulars.get(annotationName) != null) {
-            return Collections.singleton(annotation);
+            return Set.of(annotation);
         } else if (repeatables.get(annotationName) != null) {
             // repeatable, we need to extract actual annotations
             return Annotations.onlyRuntimeVisible(Arrays.asList(annotation.value().asNestedArray()));
         } else {
             // neither singular nor repeatable, return empty collection
-            return Collections.emptyList();
+            return List.of();
         }
     }
 

independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/BeanResolverImpl.java

@@ -47,9 +47,9 @@ public Set<BeanInfo> resolveBeans(Type requiredType, Set<AnnotationInstance> req
         List<BeanInfo> beans = findMatching(typeAndQualifiers);
         Set<BeanInfo> ret;
         if (beans.isEmpty()) {
-            ret = Collections.emptySet();
+            ret = Set.of();
         } else if (beans.size() == 1) {
-            ret = Collections.singleton(beans.get(0));
+            ret = Set.of(beans.get(0));
         } else {
             ret = new HashSet<>(beans);
         }

independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/InjectionPointInfo.java

@@ -5,7 +5,6 @@
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.ListIterator;
@@ -134,7 +133,7 @@ static InjectionPointInfo fromSyntheticInjectionPoint(TypeAndQualifiers typeAndQ
     InjectionPointInfo(Type requiredType, Set<AnnotationInstance> requiredQualifiers, InjectionPointKind kind,
             AnnotationTarget target, AnnotationTarget methodParameterTarget, boolean isTransientReference, boolean isDelegate) {
         this(new TypeAndQualifiers(requiredType, requiredQualifiers.isEmpty()
-                ? Collections.singleton(AnnotationInstance.create(DotNames.DEFAULT, null, Collections.emptyList()))
+                ? Set.of(AnnotationInstance.create(DotNames.DEFAULT, null, List.of()))
                 : requiredQualifiers),
                 kind, target, methodParameterTarget, isTransientReference, isDelegate);
     }

independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/Interceptors.java

@@ -70,7 +70,7 @@ static InterceptorInfo createInterceptor(ClassInfo interceptorClass, BeanDeploym
         checkInterceptorFieldsAndMethods(interceptorClass, beanDeployment);
 
         return new InterceptorInfo(interceptorClass, beanDeployment,
-                bindings.size() == 1 ? Collections.singleton(bindings.iterator().next())
+                bindings.size() == 1 ? Set.of(bindings.iterator().next())
                         : Collections.unmodifiableSet(bindings),
                 Injection.forBean(interceptorClass, null, beanDeployment, transformer, Injection.BeanType.INTERCEPTOR),
                 priority);

independent-projects/arc/runtime/src/main/java/io/quarkus/arc/impl/ContextDataMap.java

@@ -82,7 +82,7 @@ public Set<Map.Entry<String, Object>> entrySet() {
         final AbstractMap.SimpleImmutableEntry<String, Object> firstEntry = new AbstractMap.SimpleImmutableEntry<>(
                 ArcInvocationContext.KEY_INTERCEPTOR_BINDINGS, interceptorBindings);
         if (delegate == null) {
-            return Collections.singleton(firstEntry);
+            return Set.of(firstEntry);
         } else {
             Set<Map.Entry<String, Object>> entries = new HashSet<>(delegate.size() + 1);
             entries.addAll(delegate.entrySet());
@@ -107,7 +107,7 @@ public boolean isEmpty() {
     @Override
     public Set<String> keySet() {
         if (delegate == null) {
-            return Collections.singleton(ArcInvocationContext.KEY_INTERCEPTOR_BINDINGS);
+            return Set.of(ArcInvocationContext.KEY_INTERCEPTOR_BINDINGS);
         } else {
             Set<String> set = new HashSet<>(delegate.size() + 1);
             set.addAll(delegate.keySet());
@@ -145,7 +145,7 @@ public int size() {
     @Override
     public Collection<Object> values() {
         if (delegate == null) {
-            return Collections.singleton(interceptorBindings);
+            return Set.of(interceptorBindings);
         } else {
             List<Object> list = new ArrayList<>(delegate.size() + 1);
             list.addAll(delegate.values());

independent-projects/arc/runtime/src/main/java/io/quarkus/arc/impl/Qualifiers.java

@@ -6,7 +6,6 @@
 import java.lang.reflect.Method;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
@@ -20,7 +19,7 @@ public final class Qualifiers {
 
     public static final Set<Annotation> DEFAULT_QUALIFIERS = Set.of(Default.Literal.INSTANCE, Any.Literal.INSTANCE);
 
-    public static final Set<Annotation> IP_DEFAULT_QUALIFIERS = Collections.singleton(Default.Literal.INSTANCE);
+    public static final Set<Annotation> IP_DEFAULT_QUALIFIERS = Set.of(Default.Literal.INSTANCE);
 
     final Set<String> allQualifiers;
     // custom qualifier -> non-binding members (can be empty but never null)