From 9452873d13ed421326d178a94744eba0bcec380c Mon Sep 17 00:00:00 2001
From: MiniDigger <admin@minidigger.me>
Date: Fri, 14 Aug 2020 02:40:06 +0200
Subject: [PATCH] Add initial brigadier support (implements #77) (#153)

Co-authored-by: Aikar <aikar@aikar.co>
---
 .idea/compiler.xml                            |  17 +-
 .idea/encodings.xml                           |   2 +
 .idea/inspectionProfiles/Project_Default.xml  |   1 +
 brigadier/pom.xml                             |  74 ++++++++
 .../ACFBrigadierManager.java                  | 164 ++++++++++++++++++
 .../java/co/aikar/commands/BaseCommand.java   |  10 +-
 .../co/aikar/commands/CommandParameter.java   |  28 ++-
 .../co/aikar/commands/ForwardingCommand.java  |   2 -
 .../co/aikar/commands/RegisteredCommand.java  |  11 +-
 example/pom.xml                               |   2 +-
 .../java/co/aikar/acfexample/ACFExample.java  |  12 +-
 .../co/aikar/acfexample/BrigadierTest.java    |  92 ++++++++++
 paper/pom.xml                                 |  20 ++-
 .../PaperAsyncTabCompleteHandler.java         |   4 +
 .../aikar/commands/PaperBrigadierManager.java |  78 +++++++++
 .../aikar/commands/PaperCommandManager.java   |  17 ++
 pom.xml                                       |   2 +
 17 files changed, 519 insertions(+), 17 deletions(-)
 create mode 100644 brigadier/pom.xml
 create mode 100644 brigadier/src/main/java/co.aikar.commands/ACFBrigadierManager.java
 create mode 100644 example/src/main/java/co/aikar/acfexample/BrigadierTest.java
 create mode 100644 paper/src/main/java/co/aikar/commands/PaperBrigadierManager.java

diff --git a/.idea/compiler.xml b/.idea/compiler.xml
index c61c5f2b..e9b5c8e4 100644
--- a/.idea/compiler.xml
+++ b/.idea/compiler.xml
@@ -7,20 +7,22 @@
         <sourceOutputDir name="target/generated-sources/annotations" />
         <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
         <outputRelativeToContentRoot value="true" />
+        <module name="acf-sponge" />
         <module name="acf" />
+        <module name="acf-example" />
+        <module name="example-plugin" />
+        <module name="acf-brigadier" />
+        <module name="acf-paper" />
+        <module name="acf-jda" />
+        <module name="acf-core" />
+        <module name="acf-velocity" />
         <module name="acf-bukkit" />
         <module name="acf-bungee" />
-        <module name="acf-core" />
-        <module name="acf-example" />
-        <module name="acf-jda" />
-        <module name="acf-paper" />
-        <module name="acf-sponge" />
-        <module name="acf-velocity" />
-        <module name="example-plugin" />
       </profile>
     </annotationProcessing>
     <bytecodeTargetLevel>
       <module name="acf" target="1.8" />
+      <module name="acf-brigadier" target="1.8" />
       <module name="acf-bukkit" target="1.8" />
       <module name="acf-bungee" target="1.8" />
       <module name="acf-core" target="1.8" />
@@ -36,6 +38,7 @@
   </component>
   <component name="JavacSettings">
     <option name="ADDITIONAL_OPTIONS_OVERRIDE">
+      <module name="acf-brigadier" options="-parameters" />
       <module name="acf-bukkit" options="-parameters" />
       <module name="acf-bungee" options="-parameters" />
       <module name="acf-core" options="-parameters" />
diff --git a/.idea/encodings.xml b/.idea/encodings.xml
index d07ce074..05af6095 100644
--- a/.idea/encodings.xml
+++ b/.idea/encodings.xml
@@ -2,6 +2,8 @@
 <project version="4">
   <component name="Encoding">
     <file url="file://$PROJECT_DIR$" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/brigadier" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/brigadier/src/main/java" charset="UTF-8" />
     <file url="file://$PROJECT_DIR$/bukkit" charset="UTF-8" />
     <file url="file://$PROJECT_DIR$/bukkit/src/main/java" charset="UTF-8" />
     <file url="file://$PROJECT_DIR$/bungee" charset="UTF-8" />
diff --git a/.idea/inspectionProfiles/Project_Default.xml b/.idea/inspectionProfiles/Project_Default.xml
index b70af4c1..0dfa5228 100644
--- a/.idea/inspectionProfiles/Project_Default.xml
+++ b/.idea/inspectionProfiles/Project_Default.xml
@@ -35,6 +35,7 @@
       <option name="IGNORE_POINT_TO_ITSELF" value="false" />
       <option name="myAdditionalJavadocTags" value="" />
     </inspection_tool>
+    <inspection_tool class="MissingJSR305" enabled="false" level="ERROR" enabled_by_default="false" />
     <inspection_tool class="SameParameterValue" enabled="false" level="WARNING" enabled_by_default="false" />
     <inspection_tool class="SpellCheckingInspection" enabled="false" level="TYPO" enabled_by_default="false">
       <option name="processCode" value="true" />
diff --git a/brigadier/pom.xml b/brigadier/pom.xml
new file mode 100644
index 00000000..4109ca75
--- /dev/null
+++ b/brigadier/pom.xml
@@ -0,0 +1,74 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright (c) 2016-2017 Daniel Ennis (Aikar) - MIT License
+  ~
+  ~  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.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>co.aikar</groupId>
+        <artifactId>acf-parent</artifactId>
+        <version><!--VERSION-->0.5.0-SNAPSHOT<!--VERSION--></version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>acf-brigadier</artifactId>
+    <version><!--VERSION-->0.5.0-SNAPSHOT<!--VERSION--></version>
+
+    <name>ACF (Brigadier)</name>
+
+    <repositories>
+        <repository>
+            <id>mojang-repo</id>
+            <url>https://libraries.minecraft.net/</url>
+        </repository>
+    </repositories>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <configuration>
+                    <shadedArtifactAttached>true</shadedArtifactAttached>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+    <dependencies>
+        <dependency>
+            <groupId>co.aikar</groupId>
+            <artifactId>acf-core</artifactId>
+            <version><!--VERSION-->0.5.0-SNAPSHOT<!--VERSION--></version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.mojang</groupId>
+            <artifactId>brigadier</artifactId>
+            <version>1.0.17</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+</project>
diff --git a/brigadier/src/main/java/co.aikar.commands/ACFBrigadierManager.java b/brigadier/src/main/java/co.aikar.commands/ACFBrigadierManager.java
new file mode 100644
index 00000000..1787abd8
--- /dev/null
+++ b/brigadier/src/main/java/co.aikar.commands/ACFBrigadierManager.java
@@ -0,0 +1,164 @@
+package co.aikar.commands;
+
+import com.mojang.brigadier.Command;
+import com.mojang.brigadier.arguments.ArgumentType;
+import com.mojang.brigadier.arguments.BoolArgumentType;
+import com.mojang.brigadier.arguments.DoubleArgumentType;
+import com.mojang.brigadier.arguments.FloatArgumentType;
+import com.mojang.brigadier.arguments.IntegerArgumentType;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.builder.RequiredArgumentBuilder;
+import com.mojang.brigadier.suggestion.SuggestionProvider;
+import com.mojang.brigadier.tree.CommandNode;
+import com.mojang.brigadier.tree.LiteralCommandNode;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.BiPredicate;
+import java.util.function.Predicate;
+
+/**
+ * Handles registering of commands into brigadier
+ *
+ * @param <S>
+ * @author MiniDigger
+ * @deprecated Unstable API
+ */
+@Deprecated
+@UnstableAPI
+public class ACFBrigadierManager<S> {
+
+    protected final CommandManager<?, ?, ?, ?, ?, ?> manager;
+
+    private final Map<Class<?>, ArgumentType<?>> arguments = new HashMap<>();
+
+    /**
+     * Constructs a new brigadier manager, utilizing the currently active command manager
+     *
+     * @param manager
+     */
+    ACFBrigadierManager(CommandManager<?, ?, ?, ?, ?, ?> manager) {
+        manager.verifyUnstableAPI("brigadier");
+
+        this.manager = manager;
+
+        // TODO support stuff like min max via brigadier?
+        registerArgument(String.class, StringArgumentType.word());
+        registerArgument(float.class, FloatArgumentType.floatArg());
+        registerArgument(Float.class, FloatArgumentType.floatArg());
+        registerArgument(double.class, DoubleArgumentType.doubleArg());
+        registerArgument(Double.class, DoubleArgumentType.doubleArg());
+        registerArgument(boolean.class, BoolArgumentType.bool());
+        registerArgument(Boolean.class, BoolArgumentType.bool());
+        registerArgument(int.class, IntegerArgumentType.integer());
+        registerArgument(Integer.class, IntegerArgumentType.integer());
+        // We use integer for long due to Bungee bug, plus should really be considered same on client
+        registerArgument(long.class, IntegerArgumentType.integer());
+        registerArgument(Long.class, IntegerArgumentType.integer());
+    }
+
+    <T> void registerArgument(Class<T> clazz, ArgumentType<?> type) {
+        arguments.put(clazz, type);
+    }
+
+    ArgumentType<Object> getArgumentTypeByClazz(CommandParameter param) {
+        if (param.consumesRest) {
+            //noinspection unchecked
+            return (ArgumentType<Object>) (ArgumentType<?>) StringArgumentType.greedyString();
+        }
+        //noinspection unchecked
+        return (ArgumentType<Object>) arguments.getOrDefault(param.getType(), StringArgumentType.string());
+    }
+
+    /**
+     * Registers the given RootCommand into the given brigadir command node, utilizing the provided suggestion provider, executor and permission predicate.<br>
+     * <p>
+     * It recreates the root command node!
+     */
+    LiteralCommandNode<S> register(RootCommand rootCommand,
+                                   LiteralCommandNode<S> root,
+                                   SuggestionProvider<S> suggestionProvider,
+                                   Command<S> executor,
+                                   BiPredicate<RootCommand, S> permCheckerRoot,
+                                   BiPredicate<RegisteredCommand, S> permCheckerSub) {
+        // recreate root to get rid of bukkits default arg
+        LiteralArgumentBuilder<S> rootBuilder = LiteralArgumentBuilder.<S>literal(root.getLiteral())
+                .requires(sender -> permCheckerRoot.test(rootCommand, sender));
+
+        root = rootBuilder.build();
+        boolean isForwardingCommand = rootCommand.getDefCommand() instanceof ForwardingCommand;
+
+        for (Map.Entry<String, RegisteredCommand> subCommand : rootCommand.getSubCommands().entries()) {
+            if ((BaseCommand.isSpecialSubcommand(subCommand.getKey()) && !isForwardingCommand) || (!subCommand.getKey().equals("help") && subCommand.getValue().prefSubCommand.equals("help"))) {
+                // don't register stuff like __catchunknown and don't help command aliases
+                continue;
+            }
+
+            // handle sub sub commands
+            String commandName = subCommand.getKey();
+            CommandNode<S> currentParent = root;
+            CommandNode<S> subCommandNode;
+            Predicate<S> subPermChecker = sender -> permCheckerSub.test(subCommand.getValue(), sender);
+            if (!isForwardingCommand) {
+                if (commandName.contains(" ")) {
+                    String[] split = ACFPatterns.SPACE.split(commandName);
+                    for (int i = 0; i < split.length - 1; i++) {
+                        if (currentParent.getChild(split[i]) == null) {
+                            LiteralCommandNode<S> sub = LiteralArgumentBuilder.<S>literal(split[i])
+                                    .requires(subPermChecker).build();
+                            currentParent.addChild(sub);
+                            currentParent = sub;
+                        } else {
+                            currentParent = currentParent.getChild(split[i]);
+                        }
+                    }
+                    commandName = split[split.length - 1];
+                }
+
+                subCommandNode = currentParent.getChild(commandName);
+                if (subCommandNode == null) {
+                    LiteralArgumentBuilder<S> argumentBuilder = LiteralArgumentBuilder.<S>literal(commandName)
+                            .requires(subPermChecker);
+
+                    // if we have no params, this command is actually executable
+                    if (subCommand.getValue().consumeInputResolvers == 0) {
+                        argumentBuilder.executes(executor);
+                    }
+                    subCommandNode = argumentBuilder.build();
+                }
+            } else {
+                subCommandNode = root;
+            }
+
+            CommandNode<S> paramNode = subCommandNode;
+            CommandParameter[] parameters = subCommand.getValue().parameters;
+            for (int i = 0; i < parameters.length; i++) {
+                CommandParameter param = parameters[i];
+                CommandParameter nextParam = param.getNextParam();
+                if (param.isCommandIssuer() || (param.canExecuteWithoutInput() && nextParam != null && !nextParam.canExecuteWithoutInput())) {
+                    continue;
+                }
+                RequiredArgumentBuilder<S, Object> builder = RequiredArgumentBuilder
+                        .<S, Object>argument(param.getName(), getArgumentTypeByClazz(param))
+                        .suggests(suggestionProvider)
+                        .requires(sender -> permCheckerSub.test(subCommand.getValue(), sender));
+
+                if (nextParam != null && nextParam.canExecuteWithoutInput()) {
+                    builder.executes(executor);
+                }
+
+                CommandNode<S> subSubCommand = builder.build();
+                paramNode.addChild(subSubCommand);
+                paramNode = subSubCommand;
+            }
+
+            if (!isForwardingCommand) {
+                currentParent.addChild(subCommandNode);
+            }
+        }
+
+        return root;
+    }
+
+}
diff --git a/core/src/main/java/co/aikar/commands/BaseCommand.java b/core/src/main/java/co/aikar/commands/BaseCommand.java
index 560b5604..24d1a346 100644
--- a/core/src/main/java/co/aikar/commands/BaseCommand.java
+++ b/core/src/main/java/co/aikar/commands/BaseCommand.java
@@ -662,7 +662,7 @@ public abstract class BaseCommand {
         String argString = ApacheCommonsLangUtil.join(args, " ").toLowerCase(Locale.ENGLISH);
         for (Map.Entry<String, RegisteredCommand> entry : subCommands.entries()) {
             final String key = entry.getKey();
-            if (key.startsWith(argString) && !CATCHUNKNOWN.equals(key) && !DEFAULT.equals(key)) {
+            if (key.startsWith(argString) && !isSpecialSubcommand(key)) {
                 final RegisteredCommand value = entry.getValue();
                 if (!value.hasPermission(issuer) || value.isPrivate) {
                     continue;
@@ -675,6 +675,10 @@ public abstract class BaseCommand {
         return new ArrayList<>(cmds);
     }
 
+    static boolean isSpecialSubcommand(String key) {
+        return CATCHUNKNOWN.equals(key) || DEFAULT.equals(key);
+    }
+
     /**
      * Complete a command properly per issuer and input.
      *
@@ -839,4 +843,8 @@ public abstract class BaseCommand {
         registeredCommands.addAll(this.subCommands.values());
         return registeredCommands;
     }
+
+    protected SetMultimap<String, RegisteredCommand> getSubCommands() {
+        return subCommands;
+    }
 }
diff --git a/core/src/main/java/co/aikar/commands/CommandParameter.java b/core/src/main/java/co/aikar/commands/CommandParameter.java
index ba4f7ec5..dfeb0de2 100644
--- a/core/src/main/java/co/aikar/commands/CommandParameter.java
+++ b/core/src/main/java/co/aikar/commands/CommandParameter.java
@@ -66,9 +66,13 @@ public class CommandParameter<CEC extends CommandExecutionContext<CEC, ? extends
     private boolean canConsumeInput;
     private boolean optionalResolver;
     boolean consumesRest;
+    private boolean isLast;
+    private boolean isOptionalInput;
+    private CommandParameter<CEC> nextParam;
 
     public CommandParameter(RegisteredCommand<CEC> command, Parameter param, int paramIndex, boolean isLast) {
         this.parameter = param;
+        this.isLast = isLast;
         this.type = param.getType();
         this.name = param.getName(); // do we care for an annotation to supply name?
         this.manager = command.manager;
@@ -99,10 +103,12 @@ public class CommandParameter<CEC extends CommandExecutionContext<CEC, ? extends
         this.values = annotations.getAnnotationValues(param, Values.class, Annotations.REPLACEMENTS | Annotations.NO_EMPTY);
 
         this.syntax = null;
+        this.isOptionalInput = !requiresInput && canConsumeInput;
+
         if (!commandIssuer) {
             this.syntax = annotations.getAnnotationValue(param, Syntax.class);
             if (syntax == null) {
-                if (!requiresInput && canConsumeInput) {
+                if (isOptionalInput) {
                     this.syntax = "[" + name + "]";
                 } else if (requiresInput) {
                     this.syntax = "<" + name + ">";
@@ -184,6 +190,10 @@ public class CommandParameter<CEC extends CommandExecutionContext<CEC, ? extends
         this.resolver = resolver;
     }
 
+    public boolean isOptionalInput() {
+        return isOptionalInput;
+    }
+
     public boolean isOptional() {
         return optional;
     }
@@ -275,4 +285,20 @@ public class CommandParameter<CEC extends CommandExecutionContext<CEC, ? extends
     public Set<String> getRequiredPermissions() {
         return permissions;
     }
+
+    public void setNextParam(CommandParameter<CEC> nextParam) {
+        this.nextParam = nextParam;
+    }
+
+    public CommandParameter<CEC> getNextParam() {
+        return nextParam;
+    }
+
+    public boolean canExecuteWithoutInput() {
+        return (!canConsumeInput || isOptionalInput()) && (nextParam == null || nextParam.canExecuteWithoutInput());
+    }
+
+    public boolean isLast() {
+        return isLast;
+    }
 }
diff --git a/core/src/main/java/co/aikar/commands/ForwardingCommand.java b/core/src/main/java/co/aikar/commands/ForwardingCommand.java
index 438528dd..67e6e798 100644
--- a/core/src/main/java/co/aikar/commands/ForwardingCommand.java
+++ b/core/src/main/java/co/aikar/commands/ForwardingCommand.java
@@ -23,8 +23,6 @@
 
 package co.aikar.commands;
 
-import co.aikar.commands.apachecommonslang.ApacheCommonsLangUtil;
-
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
diff --git a/core/src/main/java/co/aikar/commands/RegisteredCommand.java b/core/src/main/java/co/aikar/commands/RegisteredCommand.java
index 6241e170..ba809435 100644
--- a/core/src/main/java/co/aikar/commands/RegisteredCommand.java
+++ b/core/src/main/java/co/aikar/commands/RegisteredCommand.java
@@ -84,7 +84,7 @@ public class RegisteredCommand<CEC extends CommandExecutionContext<CEC, ? extend
         this.manager = this.scope.manager;
         final Annotations annotations = this.manager.getAnnotations();
 
-        if (BaseCommand.CATCHUNKNOWN.equals(prefSubCommand) || BaseCommand.DEFAULT.equals(prefSubCommand)) {
+        if (BaseCommand.isSpecialSubcommand(prefSubCommand)) {
             prefSubCommand = "";
             command = command.trim();
         }
@@ -110,8 +110,13 @@ public class RegisteredCommand<CEC extends CommandExecutionContext<CEC, ? extend
         int optionalResolvers = 0;
         StringBuilder syntaxBuilder = new StringBuilder(64);
 
+        CommandParameter<CEC> previousParam = null;
         for (int i = 0; i < parameters.length; i++) {
             CommandParameter<CEC> parameter = this.parameters[i] = new CommandParameter<>(this, parameters[i], i, i == parameters.length - 1);
+            if (previousParam != null) {
+                previousParam.setNextParam(parameter);
+            }
+            previousParam = parameter;
             if (!parameter.isCommandIssuer()) {
                 if (!parameter.requiresInput()) {
                     optionalResolvers++;
@@ -247,9 +252,9 @@ public class RegisteredCommand<CEC extends CommandExecutionContext<CEC, ? extend
                 } else if (allowOptional && parameter.isOptional()) {
                     Object value;
                     if (!parameter.isOptionalResolver() || !this.manager.hasPermission(sender, parameterPermissions)) {
-                       value = null;
+                        value = null;
                     } else {
-                       value = resolver.getContext(context);
+                        value = resolver.getContext(context);
                     }
 
                     if (value == null && parameter.getClass().isPrimitive()) {
diff --git a/example/pom.xml b/example/pom.xml
index 26843cd0..7010b64c 100644
--- a/example/pom.xml
+++ b/example/pom.xml
@@ -111,7 +111,7 @@
         <dependency>
             <groupId>com.destroystokyo.paper</groupId>
             <artifactId>paper-api</artifactId>
-            <version>1.13.2-R0.1-SNAPSHOT</version>
+            <version>1.15.2-R0.1-SNAPSHOT</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
diff --git a/example/src/main/java/co/aikar/acfexample/ACFExample.java b/example/src/main/java/co/aikar/acfexample/ACFExample.java
index 51a1c1dd..b9901f41 100644
--- a/example/src/main/java/co/aikar/acfexample/ACFExample.java
+++ b/example/src/main/java/co/aikar/acfexample/ACFExample.java
@@ -23,10 +23,11 @@
 
 package co.aikar.acfexample;
 
-import co.aikar.commands.PaperCommandManager;
 import co.aikar.commands.ConditionFailedException;
 import co.aikar.commands.MessageKeys;
 import co.aikar.commands.MessageType;
+import co.aikar.commands.PaperBrigadierManager;
+import co.aikar.commands.PaperCommandManager;
 import org.bukkit.plugin.java.JavaPlugin;
 
 import java.util.Arrays;
@@ -46,6 +47,9 @@ public final class ACFExample extends JavaPlugin {
         // 1: Create Command Manager for your respective platform
         commandManager = new PaperCommandManager(this);
 
+        // enable brigadier integration for paper servers
+        commandManager.enableUnstableAPI("brigadier");
+
         // optional: enable unstable api to use help
         commandManager.enableUnstableAPI("help");
 
@@ -109,6 +113,12 @@ public final class ACFExample extends JavaPlugin {
             getLogger().warning("Error occurred while executing command " + command.getName());
             return false; // mark as unhandeled, sender will see default message
         });
+
+        // test command for brigadier
+        commandManager.getCommandCompletions().registerAsyncCompletion("someobject", c ->
+                Arrays.asList("1", "2", "3", "4", "5")
+        );
+        commandManager.registerCommand(new BrigadierTest());
     }
 
     // Typical Bukkit Plugin Scaffolding
diff --git a/example/src/main/java/co/aikar/acfexample/BrigadierTest.java b/example/src/main/java/co/aikar/acfexample/BrigadierTest.java
new file mode 100644
index 00000000..e6fc4c63
--- /dev/null
+++ b/example/src/main/java/co/aikar/acfexample/BrigadierTest.java
@@ -0,0 +1,92 @@
+package co.aikar.acfexample;
+
+import co.aikar.commands.BaseCommand;
+import co.aikar.commands.CommandHelp;
+import co.aikar.commands.annotation.CommandAlias;
+import co.aikar.commands.annotation.CommandCompletion;
+import co.aikar.commands.annotation.CommandPermission;
+import co.aikar.commands.annotation.Default;
+import co.aikar.commands.annotation.Description;
+import co.aikar.commands.annotation.Flags;
+import co.aikar.commands.annotation.HelpCommand;
+import co.aikar.commands.annotation.Optional;
+import co.aikar.commands.annotation.Single;
+import co.aikar.commands.annotation.Subcommand;
+import co.aikar.commands.annotation.Syntax;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+
+@CommandAlias("brigadiertest")
+public class BrigadierTest extends BaseCommand {
+
+    @Subcommand("hello")
+    @Syntax("<player>")
+    @CommandCompletion("@players")
+    @Description("Says hello to a player")
+    public static void onHello(Player player, @Flags("other") Player arg) {
+        player.sendMessage("You said hello to " + arg.getDisplayName());
+    }
+
+    @Default
+    @HelpCommand
+    public static void onHelp(CommandSender sender, CommandHelp help) {
+        help.showHelp();
+    }
+
+    @Subcommand("test|test2")
+    @Description("Says hello to a player")
+    @CommandCompletion("true|false @range:20 @range:1-5 @range:20-30 test|test2|foo|bar true|false")
+    public static void onTest(CommandSender sender, boolean booleanParam, float floatParam, double doubleParam, int integerParam, String stringParam, @Optional Boolean test2) {
+        sender.sendMessage("You said: " + booleanParam + " - " + floatParam + " - " + doubleParam + " - " + integerParam + " - " + stringParam + " - " + test2 + "!");
+    }
+
+    @Subcommand("custom")
+    @Description("Try custom completions")
+    @Syntax("<syntaxTest>")
+    @CommandCompletion("@someobject")
+    public static void onCustom(Player player, SomeObject object) {
+        player.sendMessage("You said: " + object);
+    }
+
+    @Subcommand("dummy admin")
+    @CommandPermission("dummy")
+    public static void onPerm(Player player) {
+        player.sendMessage("You shall pass");
+    }
+
+    @Subcommand("sub3")
+    public static void sub3(Player player, String wooo) {
+        player.sendMessage("Wooo " + wooo);
+    }
+
+    @Subcommand("sub sub")
+    public static void onSubSub(Player player, String wooo) {
+        player.sendMessage("Wooo " + wooo);
+    }
+
+    @Subcommand("sub2")
+    public static void onSub2(Player player) {
+        player.sendMessage("Sub2");
+    }
+
+    @Subcommand("sub2 sub")
+    public static void onSub2Sub(Player player, String test) {
+        player.sendMessage("Sub2 sub " + test);
+    }
+
+    @Subcommand("find|where")
+    @CommandPermission("hyperverse.find")
+    @CommandAlias("hvf|hvfind")
+    @CommandCompletion("@players")
+    public void findPlayer(final CommandSender sender, final String player) { /* stub */ }
+
+    @Subcommand("greedy")
+    public void onGreedy(Player player, String greedyString) {
+        player.sendMessage(greedyString);
+    }
+
+    @Subcommand("notgreedy")
+    public void notGreedy(Player player, @Single String notGreedy) {
+        player.sendMessage(notGreedy);
+    }
+}
diff --git a/paper/pom.xml b/paper/pom.xml
index 91cc0ef2..a60f3b54 100644
--- a/paper/pom.xml
+++ b/paper/pom.xml
@@ -46,10 +46,28 @@
             <version><!--VERSION-->0.5.0-SNAPSHOT<!--VERSION--></version>
             <scope>compile</scope>
         </dependency>
+        <dependency>
+            <groupId>co.aikar</groupId>
+            <artifactId>acf-brigadier</artifactId>
+            <version><!--VERSION-->0.5.0-SNAPSHOT<!--VERSION--></version>
+            <scope>compile</scope>
+        </dependency>
         <dependency>
             <groupId>com.destroystokyo.paper</groupId>
             <artifactId>paper-api</artifactId>
-            <version>1.12.2-R0.1-SNAPSHOT</version>
+            <version>1.15.2-R0.1-SNAPSHOT</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.destroystokyo.paper</groupId>
+            <artifactId>paper-mojangapi</artifactId>
+            <version>1.15.2-R0.1-SNAPSHOT</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.destroystokyo.paper</groupId>
+            <artifactId>paper-mojangapi</artifactId>
+            <version>1.15.2-R0.1-SNAPSHOT</version>
             <scope>provided</scope>
         </dependency>
     </dependencies>
diff --git a/paper/src/main/java/co/aikar/commands/PaperAsyncTabCompleteHandler.java b/paper/src/main/java/co/aikar/commands/PaperAsyncTabCompleteHandler.java
index f7ff035b..2ce6a3cd 100644
--- a/paper/src/main/java/co/aikar/commands/PaperAsyncTabCompleteHandler.java
+++ b/paper/src/main/java/co/aikar/commands/PaperAsyncTabCompleteHandler.java
@@ -51,6 +51,10 @@ class PaperAsyncTabCompleteHandler implements Listener {
             if (false) throw new CommandCompletions.SyncCompletionRequired(); // fake compiler due to SneakyThrows
             List<String> completions = getCompletions(buffer, event.getCompletions(), event.getSender(), true);
             if (completions != null) {
+                // if we have no completion data, client will display an error, lets just send a space instead (https://bugs.mojang.com/browse/MC-165562)
+                if (completions.size() == 1 && completions.get(0).equals("")) {
+                    completions.set(0, " ");
+                }
                 event.setCompletions(completions);
                 event.setHandled(true);
             }
diff --git a/paper/src/main/java/co/aikar/commands/PaperBrigadierManager.java b/paper/src/main/java/co/aikar/commands/PaperBrigadierManager.java
new file mode 100644
index 00000000..fc0ed497
--- /dev/null
+++ b/paper/src/main/java/co/aikar/commands/PaperBrigadierManager.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2016-2020 Daniel Ennis (Aikar) - MIT License
+ *
+ *  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 co.aikar.commands;
+
+import com.destroystokyo.paper.brigadier.BukkitBrigadierCommandSource;
+import com.destroystokyo.paper.event.brigadier.CommandRegisteredEvent;
+import org.bukkit.Bukkit;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.plugin.Plugin;
+
+/**
+ * Handles registering of commands into brigadier
+ *
+ * @author MiniDigger
+ * @deprecated Unstable API
+ */
+@Deprecated
+@UnstableAPI
+public class PaperBrigadierManager implements Listener {
+
+    private final PaperCommandManager manager;
+    private final ACFBrigadierManager<BukkitBrigadierCommandSource> brigadierManager;
+
+    public PaperBrigadierManager(Plugin plugin, PaperCommandManager manager) {
+        manager.verifyUnstableAPI("brigadier");
+        manager.log(LogLevel.INFO, "Enabled Brigadier Support!");
+
+        this.manager = manager;
+        this.brigadierManager = new ACFBrigadierManager<>(manager);
+
+        Bukkit.getPluginManager().registerEvents(this, plugin);
+    }
+
+    @EventHandler
+    public void onCommandRegister(CommandRegisteredEvent<BukkitBrigadierCommandSource> event) {
+        RootCommand acfCommand = manager.getRootCommand(event.getCommandLabel());
+        if (acfCommand != null) {
+            event.setLiteral(brigadierManager.register(
+                    acfCommand,
+                    event.getLiteral(),
+                    event.getBrigadierCommand(),
+                    event.getBrigadierCommand(),
+                    this::checkPermRoot,
+                    this::checkPermSub
+            ));
+        }
+    }
+
+    private boolean checkPermSub(RegisteredCommand registeredCommand, BukkitBrigadierCommandSource sender) {
+        return registeredCommand.hasPermission(manager.getCommandIssuer(sender.getBukkitSender()));
+    }
+
+    private boolean checkPermRoot(RootCommand rootCommand, BukkitBrigadierCommandSource sender) {
+        return rootCommand.hasAnyPermission(manager.getCommandIssuer(sender.getBukkitSender()));
+    }
+}
diff --git a/paper/src/main/java/co/aikar/commands/PaperCommandManager.java b/paper/src/main/java/co/aikar/commands/PaperCommandManager.java
index fe06bd32..6de574ff 100644
--- a/paper/src/main/java/co/aikar/commands/PaperCommandManager.java
+++ b/paper/src/main/java/co/aikar/commands/PaperCommandManager.java
@@ -28,6 +28,8 @@ import org.bukkit.plugin.Plugin;
 @SuppressWarnings("WeakerAccess")
 public class PaperCommandManager extends BukkitCommandManager {
 
+    private boolean brigadierAvailable;
+
     // If we get anything Paper specific
     public PaperCommandManager(Plugin plugin) {
         super(plugin);
@@ -37,6 +39,21 @@ public class PaperCommandManager extends BukkitCommandManager {
         } catch (ClassNotFoundException ignored) {
             // Ignored
         }
+        try {
+            Class.forName("com.destroystokyo.paper.event.brigadier.CommandRegisteredEvent");
+            brigadierAvailable = true;
+        } catch (ClassNotFoundException ignored) {
+            // Ignored
+        }
+    }
+
+    @Override
+    public void enableUnstableAPI(String api) {
+        super.enableUnstableAPI(api);
+
+        if ("brigadier".equals(api) && brigadierAvailable) {
+            new PaperBrigadierManager(plugin, this);
+        }
     }
 
     @Override
diff --git a/pom.xml b/pom.xml
index d784cf9c..4d6f6a75 100644
--- a/pom.xml
+++ b/pom.xml
@@ -197,11 +197,13 @@
 
     <modules>
         <module>core</module>
+        <module>brigadier</module>
         <module>bukkit</module>
         <module>paper</module>
         <module>bungee</module>
         <module>sponge</module>
         <module>jda</module>
         <module>velocity</module>
+        <module>example</module>
     </modules>
 </project>