Several command permission fixes

 - Attach permission checks to the first argument (so the literal
   command name) rather than the last argument. This fixes commands
   showing up when they shouldn't.

 - HelpingArgumentBuilder now inherits permissions of its leaf nodes.
   This only really impacts the "track" subcommand.

 - Don't autocomplete the computer selector for the "queue" subcommand.
   As everyone has permission for this command, it's possible to find
   all computer ids and labels in the world.

   I'm in mixed minds about this, but don't think this is an exploit -
   computer ids/labels are sent to in-range players so shouldn't be
   considered secret - but worth patching none-the-less.

projects/common/src/main/java/dan200/computercraft/shared/command/CommandComputerCraft.java

@@ -6,9 +6,12 @@
 
 import com.mojang.brigadier.CommandDispatcher;
 import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.RequiredArgumentBuilder;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.suggestion.Suggestions;
 import dan200.computercraft.core.computer.ComputerSide;
 import dan200.computercraft.core.metrics.Metrics;
+import dan200.computercraft.shared.command.arguments.ComputersArgumentType;
 import dan200.computercraft.shared.command.text.TableBuilder;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.core.ServerComputer;
@@ -169,7 +172,10 @@ public static void register(CommandDispatcher<CommandSourceStack> dispatcher) {
 
             .then(command("queue")
                 .requires(UserLevel.ANYONE)
-                .arg("computer", manyComputers())
+                .arg(
+                    RequiredArgumentBuilder.<CommandSourceStack, ComputersArgumentType.ComputersSupplier>argument("computer", manyComputers())
+                        .suggests((context, builder) -> Suggestions.empty())
+                )
                 .argManyValue("args", StringArgumentType.string(), Collections.emptyList())
                 .executes((ctx, args) -> {
                     var computers = getComputersArgument(ctx, "computer");

projects/common/src/main/java/dan200/computercraft/shared/command/UserLevel.java

@@ -49,6 +49,29 @@ public boolean test(CommandSourceStack source) {
         return source.hasPermission(toLevel());
     }
 
+    /**
+     * Take the union of two {@link UserLevel}s.
+     * <p>
+     * This satisfies the property that for all sources {@code s}, {@code a.test(s) || b.test(s) == (a ∪ b).test(s)}.
+     *
+     * @param left  The first user level to take the union of.
+     * @param right The second user level to take the union of.
+     * @return The union of two levels.
+     */
+    public static UserLevel union(UserLevel left, UserLevel right) {
+        if (left == right) return left;
+
+        // x ∪ ANYONE = ANYONE
+        if (left == ANYONE || right == ANYONE) return ANYONE;
+
+        // x ∪ OWNER = OWNER
+        if (left == OWNER) return right;
+        if (right == OWNER) return left;
+
+        // At this point, we have x != y and x, y ∈ { OP, OWNER_OP }.
+        return OWNER_OP;
+    }
+
     private static boolean isOwner(CommandSourceStack source) {
         var server = source.getServer();
         var sender = source.getEntity();

projects/common/src/main/java/dan200/computercraft/shared/command/builder/CommandBuilder.java

@@ -48,11 +48,15 @@ public CommandBuilder<S> requires(Predicate<S> predicate) {
         return this;
     }
 
-    public CommandBuilder<S> arg(String name, ArgumentType<?> type) {
-        args.add(RequiredArgumentBuilder.argument(name, type));
+    public CommandBuilder<S> arg(ArgumentBuilder<S, ?> arg) {
+        args.add(arg);
         return this;
     }
 
+    public CommandBuilder<S> arg(String name, ArgumentType<?> type) {
+        return arg(RequiredArgumentBuilder.argument(name, type));
+    }
+
     public <T> CommandNodeBuilder<S, ArgCommand<S, List<T>>> argManyValue(String name, ArgumentType<T> type, List<T> empty) {
         return argMany(name, type, () -> empty);
     }
@@ -74,7 +78,7 @@ private <T> CommandNodeBuilder<S, ArgCommand<S, List<T>>> argMany(String name, R
 
         return command -> {
             // The node for no arguments
-            var tail = tail(ctx -> command.run(ctx, empty.get()));
+            var tail = setupTail(ctx -> command.run(ctx, empty.get()));
 
             // The node for one or more arguments
             ArgumentBuilder<S, ?> moreArg = RequiredArgumentBuilder
@@ -83,7 +87,7 @@ private <T> CommandNodeBuilder<S, ArgCommand<S, List<T>>> argMany(String name, R
 
             // Chain all of them together!
             tail.then(moreArg);
-            return link(tail);
+            return buildTail(tail);
         };
     }
 
@@ -94,20 +98,16 @@ private static <T> List<T> getList(CommandContext<?> context, String name) {
 
     @Override
     public CommandNode<S> executes(Command<S> command) {
-        if (args.isEmpty()) throw new IllegalStateException("Cannot have empty arg chain builder");
-
-        return link(tail(command));
+        return buildTail(setupTail(command));
     }
 
-    private ArgumentBuilder<S, ?> tail(Command<S> command) {
-        var defaultTail = args.get(args.size() - 1);
-        defaultTail.executes(command);
-        if (requires != null) defaultTail.requires(requires);
-        return defaultTail;
+    private ArgumentBuilder<S, ?> setupTail(Command<S> command) {
+        return args.get(args.size() - 1).executes(command);
     }
 
-    private CommandNode<S> link(ArgumentBuilder<S, ?> tail) {
+    private CommandNode<S> buildTail(ArgumentBuilder<S, ?> tail) {
         for (var i = args.size() - 2; i >= 0; i--) tail = args.get(i).then(tail);
+        if (requires != null) tail.requires(requires);
         return tail.build();
     }
 }

projects/common/src/main/java/dan200/computercraft/shared/command/builder/HelpingArgumentBuilder.java

@@ -10,6 +10,7 @@
 import com.mojang.brigadier.context.CommandContext;
 import com.mojang.brigadier.tree.CommandNode;
 import com.mojang.brigadier.tree.LiteralCommandNode;
+import dan200.computercraft.shared.command.UserLevel;
 import net.minecraft.ChatFormatting;
 import net.minecraft.commands.CommandSourceStack;
 import net.minecraft.network.chat.ClickEvent;
@@ -18,6 +19,8 @@
 import javax.annotation.Nullable;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.function.Predicate;
+import java.util.stream.Stream;
 
 import static dan200.computercraft.core.util.Nullability.assertNonNull;
 import static dan200.computercraft.shared.command.text.ChatHelpers.coloured;
@@ -37,6 +40,29 @@ public static HelpingArgumentBuilder choice(String literal) {
         return new HelpingArgumentBuilder(literal);
     }
 
+    @Override
+    public LiteralArgumentBuilder<CommandSourceStack> requires(Predicate<CommandSourceStack> requirement) {
+        throw new IllegalStateException("Cannot use requires on a HelpingArgumentBuilder");
+    }
+
+    @Override
+    public Predicate<CommandSourceStack> getRequirement() {
+        // The requirement of this node is the union of all child's requirements.
+        var requirements = Stream.concat(
+            children.stream().map(ArgumentBuilder::getRequirement),
+            getArguments().stream().map(CommandNode::getRequirement)
+        ).toList();
+
+        // If all requirements are a UserLevel, take the union of those instead.
+        var userLevel = UserLevel.OWNER;
+        for (var requirement : requirements) {
+            if (!(requirement instanceof UserLevel level)) return x -> requirements.stream().anyMatch(y -> y.test(x));
+            userLevel = UserLevel.union(userLevel, level);
+        }
+
+        return userLevel;
+    }
+
     @Override
     public LiteralArgumentBuilder<CommandSourceStack> executes(final Command<CommandSourceStack> command) {
         throw new IllegalStateException("Cannot use executes on a HelpingArgumentBuilder");
@@ -80,9 +106,7 @@ private LiteralCommandNode<CommandSourceStack> buildImpl(String id, String comma
         helpCommand.node = node;
 
         // Set up a /... help command
-        var helpNode = LiteralArgumentBuilder.<CommandSourceStack>literal("help")
-            .requires(x -> getArguments().stream().anyMatch(y -> y.getRequirement().test(x)))
-            .executes(helpCommand);
+        var helpNode = LiteralArgumentBuilder.<CommandSourceStack>literal("help").executes(helpCommand);
 
         // Add all normal command children to this and the help node
         for (var child : getArguments()) {