Add async command suggestions

api/src/main/java/com/velocitypowered/api/command/Command.java

@@ -2,6 +2,7 @@ package com.velocitypowered.api.command;
 
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import org.checkerframework.checker.nullness.qual.NonNull;
 
 /**
@@ -29,6 +30,18 @@ public interface Command {
     return ImmutableList.of();
   }
 
+  /**
+   * Provides tab complete suggestions for a command for a specified {@link CommandSource}.
+   *
+   * @param source the source to run the command for
+   * @param currentArgs the current, partial arguments for this command
+   * @return tab complete suggestions
+   */
+  default CompletableFuture<List<String>> suggestAsync(CommandSource source,
+      String @NonNull [] currentArgs) {
+    return CompletableFuture.completedFuture(suggest(source, currentArgs));
+  }
+
   /**
    * Tests to check if the {@code source} has permission to use this command with the provided
    * {@code args}.

api/src/main/java/com/velocitypowered/api/command/RawCommand.java

@@ -2,6 +2,7 @@ package com.velocitypowered.api.command;
 
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import org.checkerframework.checker.nullness.qual.NonNull;
 
 /**
@@ -29,13 +30,19 @@ public interface RawCommand extends Command {
    * @param currentLine the current, partial command line for this command
    * @return tab complete suggestions
    */
-  default List<String> suggest(CommandSource source, String currentLine) {
+  default CompletableFuture<List<String>> suggest(CommandSource source, String currentLine) {
-    return ImmutableList.of();
+    return CompletableFuture.completedFuture(ImmutableList.of());
+  }
+
+  @Override
+  default CompletableFuture<List<String>> suggestAsync(CommandSource source,
+      String @NonNull [] currentArgs) {
+    return suggest(source, String.join(" ", currentArgs));
   }
 
   @Override
   default List<String> suggest(CommandSource source, String @NonNull [] currentArgs) {
-    return suggest(source, String.join(" ", currentArgs));
+    return suggestAsync(source, currentArgs).join();
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommandManager.java

@@ -157,9 +157,9 @@ public class VelocityCommandManager implements CommandManager {
    * Offer suggestions to fill in the command.
    * @param source the source for the command
    * @param cmdLine the partially completed command
-   * @return a {@link List}, possibly empty
+   * @return a {@link CompletableFuture} eventually completed with a {@link List}, possibly empty
    */
-  public List<String> offerSuggestions(CommandSource source, String cmdLine) {
+  public CompletableFuture<List<String>> offerSuggestions(CommandSource source, String cmdLine) {
     Preconditions.checkNotNull(source, "source");
     Preconditions.checkNotNull(cmdLine, "cmdLine");
 
@@ -173,7 +173,7 @@ public class VelocityCommandManager implements CommandManager {
           availableCommands.add("/" + entry.getKey());
         }
       }
-      return availableCommands.build();
+      return CompletableFuture.completedFuture(availableCommands.build());
     }
 
     String alias = cmdLine.substring(0, firstSpace);
@@ -181,14 +181,15 @@ public class VelocityCommandManager implements CommandManager {
     RawCommand command = commands.get(alias.toLowerCase(Locale.ENGLISH));
     if (command == null) {
       // No such command, so we can't offer any tab complete suggestions.
-      return ImmutableList.of();
+      return CompletableFuture.completedFuture(ImmutableList.of());
     }
 
     try {
       if (!command.hasPermission(source, args)) {
-        return ImmutableList.of();
+        return CompletableFuture.completedFuture(ImmutableList.of());
       }
-      return ImmutableList.copyOf(command.suggest(source, args));
+      return command.suggest(source, args)
+          .thenApply(ImmutableList::copyOf);
     } catch (Exception e) {
       throw new RuntimeException(
           "Unable to invoke suggestions for command " + cmdLine + " for " + source, e);
@@ -253,8 +254,8 @@ public class VelocityCommandManager implements CommandManager {
     }
 
     @Override
-    public List<String> suggest(CommandSource source, String currentLine) {
+    public CompletableFuture<List<String>> suggest(CommandSource source, String currentLine) {
-      return delegate.suggest(source, split(currentLine));
+      return delegate.suggestAsync(source, split(currentLine));
     }
 
     @Override

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -397,9 +397,10 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
       return false;
     }
 
-    List<String> suggestions = server.getCommandManager().offerSuggestions(player, command);
+    server.getCommandManager().offerSuggestions(player, command)
+        .thenAcceptAsync(suggestions -> {
           if (suggestions.isEmpty()) {
-      return false;
+            return;
           }
 
           List<Offer> offers = new ArrayList<>();
@@ -416,7 +417,8 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             resp.getOffers().addAll(offers);
             player.getConnection().write(resp);
           }
-    return true;
+        }, player.getConnection().eventLoop());
+    return true; // Sorry, handler; we're just gonna have to lie to you here.
   }
 
   private boolean handleRegularTabComplete(TabCompleteRequest packet) {
@@ -449,8 +451,9 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
   private void finishCommandTabComplete(TabCompleteRequest request, TabCompleteResponse response) {
     String command = request.getCommand().substring(1);
+    server.getCommandManager().offerSuggestions(player, command)
+        .thenAcceptAsync(offers -> {
           try {
-      List<String> offers = server.getCommandManager().offerSuggestions(player, command);
             for (String offer : offers) {
               response.getOffers().add(new Offer(offer, null));
             }
@@ -461,6 +464,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                 player.getUsername(),
                 command, e);
           }
+        }, player.getConnection().eventLoop());
   }
 
   private void finishRegularTabComplete(TabCompleteRequest request, TabCompleteResponse response) {

proxy/src/main/java/com/velocitypowered/proxy/console/VelocityConsole.java

@@ -73,7 +73,8 @@ public final class VelocityConsole extends SimpleTerminalConsole implements Cons
           try {
             boolean isCommand = parsedLine.line().indexOf(' ') == -1;
             List<String> offers = this.server.getCommandManager()
-                .offerSuggestions(this, parsedLine.line());
+                .offerSuggestions(this, parsedLine.line())
+                .join(); // Console doesn't get harmed much by this...
             for (String offer : offers) {
               if (isCommand) {
                 list.add(new Candidate(offer.substring(1)));