Fix childless redirects

Makes parseNodes consider the Command of a redirect target when no
contents can be read. For example, given a "foo" literal with a non-null
Command, and a "bar" literal forwarding to the "foo" node, the parse
results' context contains the command of the "foo" node, and the parsed node
is the "bar" node.

This follows the same logic as a regular redirect.
CommandDispatcherTest#testExecuteRedirectedMultipleTimes highlights the
parse tree contains the redirected node (`redirectNode`), while the
executed Command is that of the target node (`concreteNode`).

Fixes Mojang#46

Author: hugmanrique

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

@@ -401,6 +401,10 @@ private ParseResults<S> parseNodes(final CommandNode<S> node, final StringReader
                     potentials.add(parse);
                 }
             } else {
+                final CommandNode<S> redirect = child.getRedirect();
+                if (redirect != null && redirect.getCommand() != null) {
+                    context.withCommand(redirect.getCommand());
+                }
                 final ParseResults<S> parse = new ParseResults<>(context, reader, Collections.emptyMap());
                 if (!child.canUse(parse)) {
                     continue;

src/test/java/com/mojang/brigadier/CommandDispatcherTest.java

@@ -3,17 +3,6 @@
 
 package com.mojang.brigadier;
 
-import com.google.common.collect.Lists;
-import com.mojang.brigadier.context.CommandContext;
-import com.mojang.brigadier.context.CommandContextBuilder;
-import com.mojang.brigadier.exceptions.CommandSyntaxException;
-import com.mojang.brigadier.tree.LiteralCommandNode;
-import org.junit.Before;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-import org.mockito.Mock;
-import org.mockito.runners.MockitoJUnitRunner;
-
 import static com.mojang.brigadier.arguments.IntegerArgumentType.integer;
 import static com.mojang.brigadier.builder.LiteralArgumentBuilder.literal;
 import static com.mojang.brigadier.builder.RequiredArgumentBuilder.argument;
@@ -32,6 +21,19 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import com.google.common.collect.Lists;
+import com.mojang.brigadier.context.CommandContext;
+import com.mojang.brigadier.context.CommandContextBuilder;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.tree.CommandNode;
+import com.mojang.brigadier.tree.LiteralCommandNode;
+import java.util.Collections;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.runners.MockitoJUnitRunner;
+
 @RunWith(MockitoJUnitRunner.class)
 public class CommandDispatcherTest {
     private CommandDispatcher<Object> subject;
@@ -202,6 +204,15 @@ public void testParseIncompleteArgument() throws Exception {
         assertThat(parse.getContext().getNodes().size(), is(1));
     }
 
+    @Test
+    public void testParseChildlessRedirect() throws Exception {
+        final CommandNode<Object> target = subject.register(literal("foo").executes(command));
+        subject.register(literal("bar").redirect(target));
+
+        final ParseResults<Object> parse = subject.parse("bar", source);
+        assertThat(parse.getContext().getCommand(), equalTo(target.getCommand()));
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     public void testExecuteAmbiguiousParentSubcommand() throws Exception {