Made suggestions async

src/main/java/com/mojang/brigadier/CommandDispatcher.java

@@ -23,6 +23,12 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+import java.util.concurrent.FutureTask;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
@@ -285,11 +291,8 @@ public class CommandDispatcher<S> {
         return self;
     }
 
-    public CommandSuggestions getCompletionSuggestions(final ParseResults<S> parse) {
+    public CompletableFuture<CommandSuggestions> getCompletionSuggestions(final ParseResults<S> parse) {
         final CommandContextBuilder<S> context = parse.getContext();
-
-        final Set<String> suggestions = new LinkedHashSet<>();
-
         final CommandNode<S> parent;
         final int start;
 
@@ -309,13 +312,24 @@ public class CommandDispatcher<S> {
             start = 0;
         }
 
+        @SuppressWarnings("unchecked") final CompletableFuture<Collection<String>>[] futures = new CompletableFuture[parent.getChildren().size()];
+        int i = 0;
         for (final CommandNode<S> node : parent.getChildren()) {
-            node.listSuggestions(parse.getReader().getString().substring(start), suggestions, context);
+            futures[i++] = node.listSuggestions(parse.getReader().getString().substring(start));
         }
 
-        final List<String> result = new ArrayList<>(suggestions);
-        Collections.sort(result);
-        return new CommandSuggestions(new StringRange(start, parse.getReader().getTotalLength()), result);
+        final CompletableFuture<CommandSuggestions> result = new CompletableFuture<>();
+        CompletableFuture.allOf(futures).thenRun(() -> {
+            final Set<String> suggestions = Sets.newHashSet();
+            for (final CompletableFuture<Collection<String>> future : futures) {
+                suggestions.addAll(future.join());
+            }
+            final List<String> sorted = new ArrayList<>(suggestions);
+            Collections.sort(sorted);
+            result.complete(new CommandSuggestions(new StringRange(start, parse.getReader().getTotalLength()), sorted));
+        });
+
+        return result;
     }
 
     public RootCommandNode<S> getRoot() {

src/main/java/com/mojang/brigadier/arguments/ArgumentType.java

@@ -4,11 +4,14 @@ import com.mojang.brigadier.StringReader;
 import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
 
-import java.util.Set;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.concurrent.CompletableFuture;
 
 public interface ArgumentType<T> {
     <S> T parse(StringReader reader, CommandContextBuilder<S> contextBuilder) throws CommandSyntaxException;
 
-    default <S> void listSuggestions(final String command, final Set<String> output, final CommandContextBuilder<S> contextBuilder) {
+    default <S> CompletableFuture<Collection<String>> listSuggestions(final String command) {
+        return CompletableFuture.completedFuture(Collections.emptyList());
     }
 }

src/main/java/com/mojang/brigadier/tree/ArgumentCommandNode.java

@@ -5,14 +5,12 @@ import com.mojang.brigadier.RedirectModifier;
 import com.mojang.brigadier.StringReader;
 import com.mojang.brigadier.arguments.ArgumentType;
 import com.mojang.brigadier.builder.RequiredArgumentBuilder;
-import com.mojang.brigadier.context.CommandContext;
 import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.context.ParsedArgument;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
 
 import java.util.Collection;
-import java.util.Set;
-import java.util.function.Function;
+import java.util.concurrent.CompletableFuture;
 import java.util.function.Predicate;
 
 public class ArgumentCommandNode<S, T> extends CommandNode<S> {
@@ -57,8 +55,8 @@ public class ArgumentCommandNode<S, T> extends CommandNode<S> {
     }
 
     @Override
-    public void listSuggestions(final String command, final Set<String> output, final CommandContextBuilder<S> contextBuilder) {
-        type.listSuggestions(command, output, contextBuilder);
+    public CompletableFuture<Collection<String>> listSuggestions(final String command) {
+        return type.listSuggestions(command);
     }
 
     @Override

src/main/java/com/mojang/brigadier/tree/CommandNode.java

@@ -14,6 +14,8 @@ import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
@@ -97,7 +99,7 @@ public abstract class CommandNode<S> implements Comparable<CommandNode<S>> {
 
     public abstract void parse(StringReader reader, CommandContextBuilder<S> contextBuilder) throws CommandSyntaxException;
 
-    public abstract void listSuggestions(String command, Set<String> output, CommandContextBuilder<S> contextBuilder);
+    public abstract CompletableFuture<Collection<String>> listSuggestions(String command);
 
     public abstract ArgumentBuilder<S, ?> createBuilder();
 

src/main/java/com/mojang/brigadier/tree/LiteralCommandNode.java

@@ -4,15 +4,16 @@ import com.mojang.brigadier.Command;
 import com.mojang.brigadier.RedirectModifier;
 import com.mojang.brigadier.StringReader;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
-import com.mojang.brigadier.context.CommandContext;
 import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.context.StringRange;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
 import com.mojang.brigadier.exceptions.ParameterizedCommandExceptionType;
 
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Set;
-import java.util.function.Function;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
 import java.util.function.Predicate;
 
 public class LiteralCommandNode<S> extends CommandNode<S> {
@@ -50,9 +51,11 @@ public class LiteralCommandNode<S> extends CommandNode<S> {
     }
 
     @Override
-    public void listSuggestions(final String command, final Set<String> output, final CommandContextBuilder<S> contextBuilder) {
+    public CompletableFuture<Collection<String>> listSuggestions(final String command) {
         if (literal.startsWith(command)) {
-            output.add(literal);
+            return CompletableFuture.completedFuture(Collections.singleton(literal));
+        } else {
+            return CompletableFuture.completedFuture(Collections.emptyList());
         }
     }
 

src/main/java/com/mojang/brigadier/tree/RootCommandNode.java

@@ -5,8 +5,9 @@ import com.mojang.brigadier.builder.ArgumentBuilder;
 import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
 
+import java.util.Collection;
 import java.util.Collections;
-import java.util.Set;
+import java.util.concurrent.CompletableFuture;
 
 public class RootCommandNode<S> extends CommandNode<S> {
     public RootCommandNode() {
@@ -28,7 +29,8 @@ public class RootCommandNode<S> extends CommandNode<S> {
     }
 
     @Override
-    public void listSuggestions(final String command, final Set<String> output, final CommandContextBuilder<S> contextBuilder) {
+    public CompletableFuture<Collection<String>> listSuggestions(final String command) {
+        return CompletableFuture.completedFuture(Collections.emptyList());
     }
 
     @Override