Add default canUse and permission methods to BasicCommand (#11047)

patches/api/Brigadier-based-command-API.patch

@@ -510,8 +510,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +import java.util.Collection;
 +import java.util.Collections;
++import org.bukkit.command.CommandSender;
 +import org.jetbrains.annotations.ApiStatus;
 +import org.jetbrains.annotations.NotNull;
++import org.jetbrains.annotations.Nullable;
 +
 +/**
 + * Implementing this interface allows for easily creating "Bukkit-style" {@code String[] args} commands.
@@ -541,6 +543,28 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    default @NotNull Collection<String> suggest(final @NotNull CommandSourceStack commandSourceStack, final @NotNull String[] args) {
 +        return Collections.emptyList();
 +    }
++
++    /**
++     * Checks whether a command sender can receive and run the root command.
++     *
++     * @param sender the command sender trying to execute the command
++     * @return whether the command sender fulfills the root command requirement
++     * @see #permission()
++     */
++    @ApiStatus.OverrideOnly
++    default boolean canUse(final @NotNull CommandSender sender) {
++        return this.permission() == null || sender.hasPermission(this.permission());
++    }
++
++    /**
++     * Returns the permission for the root command used in {@link #canUse(CommandSender)} by default.
++     *
++     * @return the permission for the root command used in {@link #canUse(CommandSender)}
++     */
++    @ApiStatus.OverrideOnly
++    default @Nullable String permission() {
++        return null;
++    }
 +}
 diff --git a/src/main/java/io/papermc/paper/command/brigadier/CommandRegistrationFlag.java b/src/main/java/io/papermc/paper/command/brigadier/CommandRegistrationFlag.java
 new file mode 100644

patches/server/Brigadier-based-command-API.patch

@@ -860,11 +860,12 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    @Override
 +    public @Unmodifiable Set<String> register(final PluginMeta pluginMeta, final String label, final @Nullable String description, final Collection<String> aliases, final BasicCommand basicCommand) {
 +        final LiteralArgumentBuilder<CommandSourceStack> builder = Commands.literal(label)
++            .requires(stack -> basicCommand.canUse(stack.getSender()))
 +            .then(
 +                Commands.argument("args", StringArgumentType.greedyString())
 +                    .suggests((context, suggestionsBuilder) -> {
 +                        final String[] args = StringUtils.split(suggestionsBuilder.getRemaining());
-+                        final SuggestionsBuilder offsetSuggestionsBuilder = suggestionsBuilder.createOffset(suggestionsBuilder.getInput().lastIndexOf(' ') + 1);;
++                        final SuggestionsBuilder offsetSuggestionsBuilder = suggestionsBuilder.createOffset(suggestionsBuilder.getInput().lastIndexOf(' ') + 1);
 +
 +                        final Collection<String> suggestions = basicCommand.suggest(context.getSource(), args);
 +                        suggestions.forEach(offsetSuggestionsBuilder::suggest);