Vanished players can no longer block merchant trading

The trading system in vanilla is implemented with just one trading
player in mind. Because of that the trade screen of vanished players is
simply closed when another player attempts to trade with the villager to
make it seem like nobody else is trading with the villager to non
vanished players. These changes have low priority and may be removed at
any time, because it is easy to not allow this case to happen as a
vanished player.
resolves #46

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Containers remaining open by vanished players in certain conditions
 - Pressure plates remaining pressed by vanished players in certain conditions
+- Vanished players blocking merchant (villager / wandering trader) trading
 
 ## [1.5.6] - 2024-06-20
 ### Added

src/main/java/me/drex/vanish/mixin/AbstractVillagerMixin.java

@@ -0,0 +1,35 @@
+package me.drex.vanish.mixin;
+
+import com.llamalad7.mixinextras.injector.ModifyReturnValue;
+import me.drex.vanish.api.VanishAPI;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.npc.AbstractVillager;
+import net.minecraft.world.entity.player.Player;
+import org.jetbrains.annotations.Nullable;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(AbstractVillager.class)
+public class AbstractVillagerMixin {
+    @Shadow
+    private @Nullable Player tradingPlayer;
+
+    @ModifyReturnValue(method = "isTrading", at = @At("RETURN"))
+    private boolean vanish_allowTradingIfVanished(boolean original) {
+        if (original) {
+            assert this.tradingPlayer != null;
+            return !VanishAPI.isVanished(this.tradingPlayer);
+        }
+        return false;
+    }
+
+    @Inject(method = "setTradingPlayer", at = @At("HEAD"))
+    private void vanish_closeVanishedPlayerTradeScreen(Player player, CallbackInfo ci) {
+        if (player != null && this.tradingPlayer instanceof ServerPlayer serverPlayer) {
+            serverPlayer.closeContainer();
+        }
+    }
+}

src/main/resources/vanish.mixins.json

@@ -8,6 +8,7 @@
     "defaultRequire": 1
   },
   "mixins": [
+    "AbstractVillagerMixin",
     "CommandSourceStackMixin",
     "ContainerMixin",
     "ContainerOpenersCountMixin",