#1050: Fix empty result check for Complex Recipes

By: Doc <nachito94@msn.com>
Also-by: Bjarne Koll <lynxplay101@gmail.com>

paper-api/src/main/java/org/bukkit/inventory/CraftingRecipe.java

@@ -5,6 +5,7 @@ import org.bukkit.Keyed;
 import org.bukkit.Material;
 import org.bukkit.NamespacedKey;
 import org.bukkit.inventory.recipe.CraftingBookCategory;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 
 /**
@@ -18,7 +19,6 @@ public abstract class CraftingRecipe implements Recipe, Keyed {
 
     protected CraftingRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result) {
         Preconditions.checkArgument(key != null, "key cannot be null");
-        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
         this.key = key;
         this.output = new ItemStack(result);
     }
@@ -65,7 +65,7 @@ public abstract class CraftingRecipe implements Recipe, Keyed {
 
     /**
      * Gets the category which this recipe will appear in the recipe book under.
-     *
+     * <br>
      * Defaults to {@link CraftingBookCategory#MISC} if not set.
      *
      * @return recipe book category
@@ -77,7 +77,7 @@ public abstract class CraftingRecipe implements Recipe, Keyed {
 
     /**
      * Sets the category which this recipe will appear in the recipe book under.
-     *
+     * <br>
      * Defaults to {@link CraftingBookCategory#MISC} if not set.
      *
      * @param category recipe book category
@@ -86,4 +86,20 @@ public abstract class CraftingRecipe implements Recipe, Keyed {
         Preconditions.checkArgument(category != null, "category cannot be null");
         this.category = category;
     }
+
+    /**
+     * Checks an ItemStack to be used in constructors related to CraftingRecipe
+     * is not empty.
+     *
+     * @param result an ItemStack
+     * @return the same result ItemStack
+     * @throws IllegalArgumentException if the {@code result} is an empty item
+     * (AIR)
+     */
+    @ApiStatus.Internal
+    @NotNull
+    protected static ItemStack checkResult(@NotNull ItemStack result) {
+        Preconditions.checkArgument(result.getType() != Material.AIR, "Recipe must have non-AIR result.");
+        return result;
+    }
 }

paper-api/src/main/java/org/bukkit/inventory/ShapedRecipe.java

@@ -32,7 +32,7 @@ public class ShapedRecipe extends CraftingRecipe {
      */
     @Deprecated
     public ShapedRecipe(@NotNull ItemStack result) {
-        super(NamespacedKey.randomKey(), result);
+        this(NamespacedKey.randomKey(), result);
     }
 
     /**
@@ -42,6 +42,7 @@ public class ShapedRecipe extends CraftingRecipe {
      *
      * @param key the unique recipe key
      * @param result The item you want the recipe to create.
+     * @exception IllegalArgumentException if the {@code result} is an empty item (AIR)
      * @see ShapedRecipe#shape(String...)
      * @see ShapedRecipe#setIngredient(char, Material)
      * @see ShapedRecipe#setIngredient(char, Material, int)
@@ -49,7 +50,7 @@ public class ShapedRecipe extends CraftingRecipe {
      * @see ShapedRecipe#setIngredient(char, RecipeChoice)
      */
     public ShapedRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result) {
-        super(key, result);
+        super(key, checkResult(result));
     }
 
     /**

paper-api/src/main/java/org/bukkit/inventory/ShapelessRecipe.java

@@ -19,7 +19,7 @@ public class ShapelessRecipe extends CraftingRecipe {
 
     @Deprecated
     public ShapelessRecipe(@NotNull ItemStack result) {
-        super(NamespacedKey.randomKey(), result);
+        this(NamespacedKey.randomKey(), result);
     }
 
     /**
@@ -29,6 +29,7 @@ public class ShapelessRecipe extends CraftingRecipe {
      *
      * @param key the unique recipe key
      * @param result The item you want the recipe to create.
+     * @exception IllegalArgumentException if the {@code result} is an empty item (AIR)
      * @see ShapelessRecipe#addIngredient(Material)
      * @see ShapelessRecipe#addIngredient(MaterialData)
      * @see ShapelessRecipe#addIngredient(Material,int)
@@ -37,7 +38,7 @@ public class ShapelessRecipe extends CraftingRecipe {
      * @see ShapelessRecipe#addIngredient(int,Material,int)
      */
     public ShapelessRecipe(@NotNull NamespacedKey key, @NotNull ItemStack result) {
-        super(key, result);
+        super(key, checkResult(result));
     }
 
     /**