Added support for suggestions tabcompletions of a command input

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

@@ -2,6 +2,7 @@ package com.mojang.brigadier;
 
 import com.google.common.collect.ComparisonChain;
 import com.google.common.collect.Iterables;
+import com.google.common.collect.Sets;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
 import com.mojang.brigadier.context.CommandContext;
 import com.mojang.brigadier.context.CommandContextBuilder;
@@ -12,6 +13,7 @@ import com.mojang.brigadier.tree.LiteralCommandNode;
 import com.mojang.brigadier.tree.RootCommandNode;
 
 import java.util.List;
+import java.util.Set;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
@@ -23,7 +25,7 @@ public class CommandDispatcher<T> {
         }
     };
 
-    public static final SimpleCommandExceptionType ERROR_UNKNOWN_COMMAND = new SimpleCommandExceptionType("unknown_command", "Unknown command");
+    public static final SimpleCommandExceptionType ERROR_UNKNOWN_COMMAND = new SimpleCommandExceptionType("command.unknown", "Unknown command");
     public static final String ARGUMENT_SEPARATOR = " ";
     private static final String USAGE_OPTIONAL_OPEN = "[";
     private static final String USAGE_OPTIONAL_CLOSE = "]";
@@ -52,7 +54,11 @@ public class CommandDispatcher<T> {
                 if (child.getCommand() != null) {
                     context.withCommand(child.getCommand());
                 }
-                return parseNodes(child, remaining, context);
+                if (remaining.isEmpty()) {
+                    return context.build();
+                } else {
+                    return parseNodes(child, remaining.substring(1), context);
+                }
             } catch (CommandException ex) {
                 exception = ex;
             }
@@ -106,4 +112,28 @@ public class CommandDispatcher<T> {
 
         return result.toString();
     }
+
+    private Set<String> findSuggestions(CommandNode node, String command, CommandContextBuilder<T> contextBuilder, Set<String> result) {
+        for (CommandNode child : node.getChildren()) {
+            try {
+                CommandContextBuilder<T> context = contextBuilder.copy();
+                String remaining = child.parse(command, context);
+                if (remaining.isEmpty()) {
+                    child.listSuggestions(command, result);
+                } else {
+                    return findSuggestions(child, remaining.substring(1), context, result);
+                }
+            } catch (CommandException e) {
+                child.listSuggestions(command, result);
+            }
+        }
+
+        return result;
+    }
+
+    public String[] getCompletionSuggestions(String command, T source) {
+        final Set<String> nodes = findSuggestions(root, command, new CommandContextBuilder<>(source), Sets.newLinkedHashSet());
+
+        return nodes.toArray(new String[nodes.size()]);
+    }
 }

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

@@ -3,6 +3,10 @@ package com.mojang.brigadier.arguments;
 import com.mojang.brigadier.context.ParsedArgument;
 import com.mojang.brigadier.exceptions.CommandException;
 
+import java.util.Set;
+
 public interface CommandArgumentType<T> {
     ParsedArgument<T> parse(String command) throws CommandException;
+
+    void listSuggestions(String command, Set<String> output);
 }

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

@@ -7,10 +7,12 @@ import com.mojang.brigadier.context.ParsedArgument;
 import com.mojang.brigadier.exceptions.CommandException;
 import com.mojang.brigadier.exceptions.ParameterizedCommandExceptionType;
 
+import java.util.Set;
+
 public class IntegerArgumentType implements CommandArgumentType<Integer> {
-    public static final ParameterizedCommandExceptionType ERROR_NOT_A_NUMBER = new ParameterizedCommandExceptionType("argument-integer-invalid", "Expected an integer, found '${found}'", "found");
-    public static final ParameterizedCommandExceptionType ERROR_TOO_SMALL = new ParameterizedCommandExceptionType("argument-integer-low", "Integer must not be less than ${minimum}, found ${found}", "found", "minimum");
-    public static final ParameterizedCommandExceptionType ERROR_TOO_BIG = new ParameterizedCommandExceptionType("argument-integer-big", "Integer must not be more than ${maximum}, found ${found}", "found", "maximum");
+    public static final ParameterizedCommandExceptionType ERROR_NOT_A_NUMBER = new ParameterizedCommandExceptionType("argument.integer.invalid", "Expected an integer, found '${found}'", "found");
+    public static final ParameterizedCommandExceptionType ERROR_TOO_SMALL = new ParameterizedCommandExceptionType("argument.integer.low", "Integer must not be less than ${minimum}, found ${found}", "found", "minimum");
+    public static final ParameterizedCommandExceptionType ERROR_TOO_BIG = new ParameterizedCommandExceptionType("argument.integer.big", "Integer must not be more than ${maximum}, found ${found}", "found", "maximum");
 
     private static final Splitter SPLITTER = Splitter.on(CommandDispatcher.ARGUMENT_SEPARATOR).limit(2);
 
@@ -58,6 +60,10 @@ public class IntegerArgumentType implements CommandArgumentType<Integer> {
         }
     }
 
+    @Override
+    public void listSuggestions(String command, Set<String> output) {
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

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

@@ -6,6 +6,8 @@ import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.context.ParsedArgument;
 import com.mojang.brigadier.exceptions.CommandException;
 
+import java.util.Set;
+
 public class ArgumentCommandNode<T> extends CommandNode {
     private static final String USAGE_ARGUMENT_OPEN = "<";
     private static final String USAGE_ARGUMENT_CLOSE = ">";
@@ -46,12 +48,17 @@ public class ArgumentCommandNode<T> extends CommandNode {
         contextBuilder.withNode(this, parsed.getRaw());
 
         if (command.length() > start) {
-            return command.substring(start + 1);
+            return command.substring(start);
         } else {
             return "";
         }
     }
 
+    @Override
+    public void listSuggestions(String command, Set<String> output) {
+        type.listSuggestions(command, output);
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

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

@@ -7,6 +7,7 @@ import com.mojang.brigadier.exceptions.CommandException;
 
 import java.util.Collection;
 import java.util.Map;
+import java.util.Set;
 
 public abstract class CommandNode {
     private final Map<Object, CommandNode> children = Maps.newLinkedHashMap();
@@ -62,4 +63,6 @@ public abstract class CommandNode {
     public abstract String getUsageText();
 
     public abstract String parse(String command, CommandContextBuilder<?> contextBuilder) throws CommandException;
+
+    public abstract void listSuggestions(String command, Set<String> output);
 }

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

@@ -6,8 +6,10 @@ import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.exceptions.CommandException;
 import com.mojang.brigadier.exceptions.ParameterizedCommandExceptionType;
 
+import java.util.Set;
+
 public class LiteralCommandNode extends CommandNode {
-    public static final ParameterizedCommandExceptionType ERROR_INCORRECT_LITERAL = new ParameterizedCommandExceptionType("incorrect_literal", "Expected literal ${expected}", "expected");
+    public static final ParameterizedCommandExceptionType ERROR_INCORRECT_LITERAL = new ParameterizedCommandExceptionType("argument.literal.incorrect", "Expected literal ${expected}", "expected");
 
     private final String literal;
 
@@ -34,10 +36,17 @@ public class LiteralCommandNode extends CommandNode {
         }
 
         contextBuilder.withNode(this, literal);
-        int start = expected.length();
+        int start = literal.length();
         return command.substring(start);
     }
 
+    @Override
+    public void listSuggestions(String command, Set<String> output) {
+        if (literal.startsWith(command)) {
+            output.add(literal);
+        }
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

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

@@ -3,6 +3,8 @@ package com.mojang.brigadier.tree;
 import com.mojang.brigadier.context.CommandContextBuilder;
 import com.mojang.brigadier.exceptions.CommandException;
 
+import java.util.Set;
+
 public class RootCommandNode extends CommandNode {
     public RootCommandNode() {
         super(null);
@@ -23,6 +25,10 @@ public class RootCommandNode extends CommandNode {
         return command;
     }
 
+    @Override
+    public void listSuggestions(String command, Set<String> output) {
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;