Fix SimpleCommand suggestion offset (#1664)

* Fix command suggestion offset

* fix length error

* add test

* checkstyle

---------

Co-authored-by: Ross <2086824-trashp@users.noreply.gitlab.com>

proxy/src/main/java/com/velocitypowered/proxy/command/registrar/InvocableCommandRegistrar.java

@@ -103,13 +103,17 @@ abstract class InvocableCommandRegistrar<T extends InvocableCommand<I>,
         .requiresWithContext((context, reader) -> requirement.test(context))
         .executes(callback)
         .suggests((context, builder) -> {
+          // Offset the suggestion to the last space seperated word
+          int lastSpace = builder.getRemaining().lastIndexOf(' ') + 1;
+          final var offsetBuilder = builder.createOffset(builder.getStart() + lastSpace);
+
           final I invocation = invocationFactory.create(context);
           return command.suggestAsync(invocation).thenApply(suggestions -> {
             for (String value : suggestions) {
               Preconditions.checkNotNull(value, "suggestion");
-              builder.suggest(value);
+              offsetBuilder.suggest(value);
             }
-            return builder.build();
+            return offsetBuilder.build();
           });
         })
         .build();

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

@@ -724,7 +724,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             TabCompleteResponsePacket resp = new TabCompleteResponsePacket();
             resp.setTransactionId(packet.getTransactionId());
             resp.setStart(startPos + 1);
-            resp.setLength(packet.getCommand().length() - startPos);
+            resp.setLength(packet.getCommand().length() - startPos - 1);
             resp.getOffers().addAll(offers);
             player.getConnection().write(resp);
           }

proxy/src/test/java/com/velocitypowered/proxy/command/SuggestionsProviderTests.java

@@ -18,14 +18,17 @@
 package com.velocitypowered.proxy.command;
 
 import static com.mojang.brigadier.arguments.StringArgumentType.word;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.common.collect.ImmutableList;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
 import com.mojang.brigadier.builder.RequiredArgumentBuilder;
+import com.mojang.brigadier.suggestion.Suggestions;
 import com.velocitypowered.api.command.Command;
 import com.velocitypowered.api.command.CommandSource;
 import com.velocitypowered.api.command.RawCommand;
+import com.velocitypowered.api.command.SimpleCommand;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import org.junit.jupiter.api.Test;
@@ -286,4 +289,26 @@ public class SuggestionsProviderTests extends CommandTestSuite {
       return ImmutableList.of();
     }
   }
+
+  @Test
+  void testSuggestionOffset() {
+    final var meta = manager.metaBuilder("offset").build();
+    manager.register(meta, new SimpleCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return List.of("bump");
+      }
+    });
+
+    assertSuggestions("offset bu", "bump");
+    for (int i = 10; i < 20; i++) {
+      final Suggestions suggestions = manager.offerBrigadierSuggestions(source, "offset " + "bump ".repeat(i)).join();
+      assertEquals(7 + 5 * i, suggestions.getList().get(0).getRange().getStart());
+    }
+  }
 }