Purpur/purpur-server/minecraft-patches/sources/net/minecraft/server/commands/GameModeCommand.java.patch

--- a/net/minecraft/server/commands/GameModeCommand.java
+++ b/net/minecraft/server/commands/GameModeCommand.java
@@ -47,6 +_,18 @@
     }
 
     private static int setMode(final CommandContext<CommandSourceStack> context, final Collection<ServerPlayer> players, final GameType type) {
+        // Purpur start - Gamemode extra permissions
+        if (org.purpurmc.purpur.PurpurConfig.commandGamemodeRequiresPermission) {
+            String gamemode = type.getName();
+            CommandSourceStack sender = context.getSource();
+            if (!sender.testPermission(Permissions.COMMANDS_GAMEMASTER, "minecraft.command.gamemode." + gamemode)) {
+                return 0;
+            }
+            if (sender.getEntity() instanceof ServerPlayer player && (players.size() > 1 || !players.contains(player)) && !sender.testPermission(Permissions.COMMANDS_GAMEMASTER, "minecraft.command.gamemode." + gamemode + ".other")) {
+                return 0;
+            }
+        }
+        // Purpur end - Gamemode extra permissions
         int count = 0;
 
         for (ServerPlayer player : players) {