feat: Chex - Redundant this access transformer

Author: Pazaz

src/main/java/rs/lostcity/deob/ast/AstDeobfuscator.java

@@ -26,6 +26,7 @@ public class AstDeobfuscator {
     public AstDeobfuscator(TomlParseResult profile) {
         this.profile = profile;
 
+        registerAstTransformer(new RedundantThisTransformer());
         registerAstTransformer(new ProduceMapTransformer());
 
         // todo: GlTransformer

src/main/java/rs/lostcity/deob/ast/transform/RedundantThisTransformer.java

@@ -0,0 +1,43 @@
+package rs.lostcity.deob.ast.transform;
+
+import com.github.javaparser.ast.CompilationUnit;
+import com.github.javaparser.ast.expr.*;
+import com.github.javaparser.resolution.UnsolvedSymbolException;
+
+public class RedundantThisTransformer extends AstTransformer {
+
+    @Override
+    public void transformUnit(CompilationUnit unit) {
+        var fields = findAll(unit, FieldAccessExpr.class,
+                        expr -> isUnqualifiedThis(expr.getScope()));
+
+        for (var expr : fields) {
+            var nameExpr = new NameExpr(expr.getNameAsString());
+            expr.replace(nameExpr);
+
+            try {
+                if (nameExpr.resolve().isField()) {
+                    // still resolves to a field, `this` was redundant
+                    continue;
+                }
+            } catch (UnsolvedSymbolException e) {
+                // can't resolve, revert to be safe
+                // System.err.println("[" + getName() + "] WARNING: " + e.getMessage());
+            }
+
+            // revert since replacing `this.someName` with `someName` did not resolve to a field (shadowed)
+            nameExpr.replace(expr);
+        }
+
+        walk(unit, MethodCallExpr.class, expr -> {
+            // this.someMethod()
+            if (expr.getScope().filter(RedundantThisTransformer::isUnqualifiedThis).isPresent()) {
+                expr.setScope(null);
+            }
+        });
+    }
+
+    private static boolean isUnqualifiedThis(Expression expr) {
+        return expr instanceof ThisExpr thisExpr && thisExpr.getTypeName().isEmpty();
+    }
+}