feat: EmptyArrayLengthTransformer (#121)

* feat: EmptyArrayLengthTransformer

* use contexts and frame matches in empty-array-length-transformer and mark changes when made

Author: SpigotRCE

deobfuscator-transformers/src/main/java/uwu/narumi/deobfuscator/core/other/impl/universal/UniversalNumberTransformer.java

@@ -2,7 +2,7 @@
 
 import uwu.narumi.deobfuscator.api.transformer.ComposedTransformer;
 import uwu.narumi.deobfuscator.core.other.impl.clean.peephole.UselessPopCleanTransformer;
-import uwu.narumi.deobfuscator.core.other.impl.universal.number.InlineConstantValuesTransformer;
+import uwu.narumi.deobfuscator.core.other.impl.universal.number.*;
 
 /**
  * Simplifies number operations on constant values.
@@ -11,6 +11,7 @@ public class UniversalNumberTransformer extends ComposedTransformer {
   public UniversalNumberTransformer() {
     super(
         InlineConstantValuesTransformer::new,
+        EmptyArrayLengthTransformer::new,
 
         UselessPopCleanTransformer::new
     );

deobfuscator-transformers/src/main/java/uwu/narumi/deobfuscator/core/other/impl/universal/number/EmptyArrayLengthTransformer.java

@@ -0,0 +1,23 @@
+package uwu.narumi.deobfuscator.core.other.impl.universal.number;
+
+import uwu.narumi.deobfuscator.api.asm.MethodContext;
+import uwu.narumi.deobfuscator.api.asm.matcher.impl.*;
+import uwu.narumi.deobfuscator.api.transformer.Transformer;
+
+public class EmptyArrayLengthTransformer extends Transformer {
+  @Override protected void transform() throws Exception {
+    scopedClasses().forEach(classWrapper -> classWrapper.methods().forEach(methodNode -> {
+      MethodContext methodContext = MethodContext.of(classWrapper, methodNode);
+      OpcodeMatch.of(ARRAYLENGTH)
+        .and(FrameMatch.stack(0,
+          OpcodeMatch.of(NEWARRAY).and(FrameMatch.stack(0, NumberMatch.numInteger().capture("array-length")))))
+        .findAllMatches(methodContext)
+        .forEach(matchContext -> {
+          methodNode.instructions.insert(matchContext.insn(),
+            numberInsn(matchContext.captures().get("array-length").insn().asInteger()));
+          matchContext.removeAll();
+          markChange();
+        });
+    }));
+  }
+}