feat(core): Reuse a single instance for SuggestionProvider#noSuggestions

Author: jpenilla

cloud-core/src/main/java/org/incendo/cloud/suggestion/NoSuggestions.java

@@ -0,0 +1,54 @@
+//
+// MIT License
+//
+// Copyright (c) 2024 Incendo
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+package org.incendo.cloud.suggestion;
+
+import java.util.Collections;
+import java.util.concurrent.CompletableFuture;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.incendo.cloud.context.CommandContext;
+import org.incendo.cloud.context.CommandInput;
+
+final class NoSuggestions implements SuggestionProvider<Object> {
+
+    private static final SuggestionProvider<?> INSTANCE = new NoSuggestions();
+
+    private final CompletableFuture<? extends @NonNull Iterable<? extends @NonNull Suggestion>> result =
+            CompletableFuture.completedFuture(Collections.emptyList());
+
+    private NoSuggestions() {
+    }
+
+    @Override
+    public @NonNull CompletableFuture<? extends @NonNull Iterable<? extends @NonNull Suggestion>> suggestionsFuture(
+            final @NonNull CommandContext<Object> context,
+            final @NonNull CommandInput input
+    ) {
+        return this.result;
+    }
+
+    @SuppressWarnings("unchecked")
+    static <C> @NonNull SuggestionProvider<C> instance() {
+        return (SuggestionProvider<C>) INSTANCE;
+    }
+}

cloud-core/src/main/java/org/incendo/cloud/suggestion/SuggestionProvider.java

@@ -24,7 +24,6 @@
 package org.incendo.cloud.suggestion;
 
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.concurrent.CompletableFuture;
 import org.apiguardian.api.API;
 import org.checkerframework.checker.nullness.qual.NonNull;
@@ -66,8 +65,8 @@ public interface SuggestionProvider<C> {
      * @param <C> command sender type
      * @return suggestion provider
      */
-    static <C> SuggestionProvider<C> noSuggestions() {
-        return (ctx, in) -> CompletableFuture.completedFuture(Collections.emptyList());
+    static <C> @NonNull SuggestionProvider<C> noSuggestions() {
+        return NoSuggestions.instance();
     }
 
     /**