2 files changed, 99 insertions, 1 deletions
diff --git a/src/main/java/ftbsc/lll/tools/InsnSequence.java b/src/main/java/ftbsc/lll/tools/InsnSequence.java
index 4afd626..1e667f5 100644
--- a/src/main/java/ftbsc/lll/tools/InsnSequence.java
+++ b/src/main/java/ftbsc/lll/tools/InsnSequence.java
@@ -8,7 +8,7 @@ import java.util.Objects;
 
 /**
  * Represents a sequence of instructions contained within two given nodes.
- * Extends InsnList, but provides additional flexibility.
+ * Extends InsnList, but provides additional flexibility and features.
  */
 public class InsnSequence extends InsnList {
 	/**
@@ -55,6 +55,16 @@ public class InsnSequence extends InsnList {
 	 */
 	public void add(AbstractInsnNode... nodes) {
 		for(AbstractInsnNode node : nodes)
+			this.add(node);
+	}
+
+	/**
+	 * Wraps InsnList's add() to ignore null values.
+	 * @param node to add
+	 */
+	@Override
+	public void add(AbstractInsnNode node) {
+		if(node != null)
 			super.add(node);
 	}
 
diff --git a/src/main/java/ftbsc/lll/tools/StackTools.java b/src/main/java/ftbsc/lll/tools/StackTools.java
new file mode 100644
index 0000000..bbb663b
--- /dev/null
+++ b/src/main/java/ftbsc/lll/tools/StackTools.java
@@ -0,0 +1,88 @@
+package ftbsc.lll.tools;
+
+import com.sun.istack.internal.Nullable;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.tree.*;
+
+import java.util.Comparator;
+import java.util.Objects;
+
+/**
+ * Various methods for manipulating the stack.
+ * Includes anything from instantiation to variable manipulation - just about
+ * anything that loads stuff on or from the stack.
+ */
+public class StackTools implements Opcodes {
+	/**
+	 * Creates a new instance of an object, given its internal name, constructor descriptor and instructions to load
+	 * the parameters.
+	 * The created object is loaded on the stack.
+	 * @param name the internal name of the object to initialize, where
+	 *             the internal name of a class is its fully qualified name, where '.' are replaced by '/'
+	 * @param desc the descriptor of the constructor to call
+	 * @param args nodes containing instructions to load the constructor arguments, in the right order
+	 * @return an instruction list containing the opcodes needed to create the new object and load it on the stack.
+	 */
+	public static InsnList instantiate(String name, String desc, @Nullable AbstractInsnNode... args) {
+		InsnSequence is = new InsnSequence();
+		is.add(args);
+		return instantiate(name, desc, is);
+	}
+
+	/**
+	 * Creates a new instance of an object, given its internal name, constructor descriptor and instructions to load
+	 * the parameters.
+	 * The created object is loaded on the stack.
+	 * @param name the internal name of the object to initialize, where
+	 *             the internal name of a class is its fully qualified name, where '.' are replaced by '/'
+	 * @param desc the descriptor of the constructor to call
+	 * @param args a list of instructions loading the constructor arguments onto the stack in the correct order
+	 * @return an instruction list containing the opcodes needed to create the new object and load it on the stack.
+	 */
+	public static InsnList instantiate(String name, String desc, @Nullable InsnList args) {
+		InsnSequence list = new InsnSequence();
+		list.add(new TypeInsnNode(NEW, name), new InsnNode(DUP));
+		if (args != null) list.add(args);
+		list.add(new MethodInsnNode(INVOKESPECIAL, name, "<init>", desc, false));
+		return list;
+	}
+
+
+	/**
+	 * Creates a new local variable, lasting in scope from the first to the last label of the given method.
+	 * @param method the method for which to declare the local variable
+	 * @param name the variable's name
+	 * @param desc the type descriptor for the new variable
+	 * @return the index value of the new local variable
+	 */
+	public static int addLocalVariable(MethodNode method, String name, String desc) {
+		return addLocalVariable(
+			method, name, desc,
+			(LabelNode) PatternMatcher.builder().label().build().find(method).getFirst(),
+			(LabelNode) PatternMatcher.builder().label().reverse().build().find(method).getFirst()
+		);
+	}
+
+	/**
+	 * Creates a new local variable, lasting in scope between two given LabelNodes.
+	 * @param method the method for which to declare the local variable
+	 * @param name the variable's name
+	 * @param desc the type descriptor for the new variable
+	 * @param start the label at which the variable should enter scope
+	 * @param end the label at which the variable should go out of scope
+	 * @return the index value of the new local variable
+	 */
+	public static int addLocalVariable(MethodNode method, String name, String desc, LabelNode start, LabelNode end) {
+		final int targetIndex =
+			method.localVariables
+				.stream()
+				.max(Comparator.comparingInt(v -> v.index))
+				.map(var -> var.desc.equals("J") || var.desc.equals("D")
+					? var.index + 2 //skip two if long or double - major java moment
+					: var.index + 1)
+				.orElse(0);
+		LocalVariableNode variable = new LocalVariableNode(name, desc, null, start, end, targetIndex);
+		method.localVariables.add(variable);
+		return targetIndex;
+	}
+}