Expose isStackable on ItemComposition objects

runelite-api/src/main/java/net/runelite/api/ItemComposition.java

@@ -74,4 +74,11 @@ public interface ItemComposition
 	 * @return true if members-only, false otherwise.
 	 */
 	boolean isMembers();
+
+	/**
+	 * Returns whether or not the item stacks in the players' inventories
+	 *
+	 * @return true if stackable, false otherwise
+	 */
+	boolean isStackable();
 }

runelite-mixins/src/main/java/net/runelite/mixins/RSItemCompositionMixin.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2018, SomeoneWithAnInternetConnection
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package net.runelite.mixins;
+
+import net.runelite.api.mixins.Inject;
+import net.runelite.api.mixins.Mixin;
+import net.runelite.rs.api.RSItemComposition;
+
+@Mixin(RSItemComposition.class)
+public abstract class RSItemCompositionMixin implements RSItemComposition
+{
+	@Inject
+	@Override
+	public boolean isStackable()
+	{
+		return getIsStackable() != 0;
+	}
+}

runescape-api/src/main/java/net/runelite/rs/api/RSItemComposition.java

@@ -58,6 +58,15 @@ public interface RSItemComposition extends ItemComposition
 	@Override
 	boolean isMembers();
 
+	/**
+	 * You probably want {@link #isStackable}
+	 * <p>
+	 * This is the <b>{@code int}</b> that client code uses internally to represent this true/false value. It appears to only ever be set to 1 or 0
+	 * @return 0 when this type of item isn't stackable, 1 otherwise
+	 */
+	@Import("isStackable")
+	int getIsStackable();
+
 	@Import("maleModel")
 	int getMaleModel();
 }