core: replace removed synthetic constructor

jadx-core/src/main/java/jadx/core/dex/instructions/mods/ConstructorInsn.java

@@ -52,6 +52,13 @@ public class ConstructorInsn extends InsnNode {
 		setSourceLine(invoke.getSourceLine());
 	}
 
+	public ConstructorInsn(MethodInfo callMth, CallType callType, RegisterArg instanceArg) {
+		super(InsnType.CONSTRUCTOR, callMth.getArgsCount());
+		this.callMth = callMth;
+		this.callType = callType;
+		this.instanceArg = instanceArg;
+	}
+
 	public MethodInfo getCallMth() {
 		return callMth;
 	}
@@ -64,6 +71,10 @@ public class ConstructorInsn extends InsnNode {
 		return callMth.getDeclClass();
 	}
 
+	public CallType getCallType() {
+		return callType;
+	}
+
 	public boolean isNewInstance() {
 		return callType == CallType.CONSTRUCTOR;
 	}

jadx-core/src/main/java/jadx/core/dex/visitors/ModVisitor.java

 package jadx.core.dex.visitors;
 
+import jadx.core.codegen.TypeGen;
 import jadx.core.deobf.NameMapper;
 import jadx.core.dex.attributes.AType;
 import jadx.core.dex.info.MethodInfo;
@@ -143,6 +144,10 @@ public class ModVisitor extends AbstractVisitor {
 				if (co.isNewInstance()) {
 					removeAssignChain(instArgAssignInsn, remover, InsnType.NEW_INSTANCE);
 				}
+				ConstructorInsn replace = processConstructor(mth, co);
+				if (replace != null) {
+					replaceInsn(block, insnNumber, replace);
+				}
 			}
 		} else if (inv.getArgsCount() > 0) {
 			for (int j = 0; j < inv.getArgsCount(); j++) {
@@ -158,6 +163,42 @@ public class ModVisitor extends AbstractVisitor {
 	}
 
 	/**
+	 * Replace call of synthetic constructor
+	 */
+	private static ConstructorInsn processConstructor(MethodNode mth, ConstructorInsn co) {
+		MethodNode callMth = mth.dex().resolveMethod(co.getCallMth());
+		if (callMth != null
+				&& callMth.getAccessFlags().isSynthetic()
+				&& allArgsNull(co)) {
+			// if all arguments is null => replace with default constructor
+			ClassNode classNode = mth.dex().resolveClass(callMth.getParentClass().getClassInfo());
+			boolean passThis = co.getArgsCount() >= 1 && co.getArg(0).isThis();
+			String ctrId = "<init>(" + (passThis ? TypeGen.signature(co.getArg(0).getType()) : "") + ")V";
+			MethodNode defCtr = classNode.searchMethodByName(ctrId);
+			if (defCtr != null) {
+				ConstructorInsn newInsn = new ConstructorInsn(defCtr.getMethodInfo(), co.getCallType(), co.getInstanceArg());
+				newInsn.setResult(co.getResult());
+				return newInsn;
+			}
+		}
+		return null;
+	}
+
+	private static boolean allArgsNull(InsnNode insn) {
+		for (InsnArg insnArg : insn.getArguments()) {
+			if (insnArg.isLiteral()) {
+				LiteralArg lit = (LiteralArg) insnArg;
+				if (lit.getLiteral() != 0) {
+					return false;
+				}
+			} else if (!insnArg.isThis()) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	/**
 	 * Remove instructions on 'move' chain until instruction with type 'insnType'
 	 */
 	private static void removeAssignChain(InsnNode insn, InstructionRemover remover, InsnType insnType) {

jadx-core/src/test/java/jadx/tests/api/IntegrationTest.java

@@ -121,6 +121,11 @@ public abstract class IntegrationTest extends TestUtils {
 			public boolean isShowInconsistentCode() {
 				return true;
 			}
+
+			@Override
+			public int getThreadsCount() {
+				return 1;
+			}
 		}, new File(outDir));
 	}
 

jadx-core/src/test/java/jadx/tests/integration/inner/TestInnerClass4.java

+package jadx.tests.integration.inner;
+
+import jadx.core.dex.nodes.ClassNode;
+import jadx.tests.api.IntegrationTest;
+
+import org.junit.Test;
+
+import static jadx.tests.api.utils.JadxMatchers.containsOne;
+import static org.junit.Assert.assertThat;
+
+public class TestInnerClass4 extends IntegrationTest {
+
+	public static class TestCls {
+		public class C {
+			public String c;
+
+			private C() {
+				this.c = "c";
+			}
+		}
+
+		private String test() {
+			return new C().c;
+		}
+	}
+
+	@Test
+	public void test() {
+		ClassNode cls = getClassNode(TestCls.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("return new C().c;"));
+	}
+}