fix: make correct replacement for synthetic constructor (#808)

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

@@ -2,6 +2,8 @@ package jadx.core.dex.visitors;
 
 import java.util.ArrayList;
 
+import org.jetbrains.annotations.Nullable;
+
 import jadx.core.codegen.TypeGen;
 import jadx.core.dex.info.MethodInfo;
 import jadx.core.dex.instructions.InsnType;
@@ -105,8 +107,12 @@ public class ConstructorVisitor extends AbstractVisitor {
 	}
 
 	/**
-	 * Replace call of synthetic constructor
+	 * Replace call of synthetic constructor with all 'null' args
+	 * to a non-synthetic or default constructor if possible.
+	 *
+	 * @return insn for replacement or null if replace not needed or not possible.
 	 */
+	@Nullable
 	private static ConstructorInsn processConstructor(MethodNode mth, ConstructorInsn co) {
 		MethodNode callMth = mth.dex().resolveMethod(co.getCallMth());
 		if (callMth == null
@@ -125,11 +131,11 @@ public class ConstructorVisitor extends AbstractVisitor {
 		boolean passThis = instanceArg.isThis();
 		String ctrId = "<init>(" + (passThis ? TypeGen.signature(instanceArg.getInitType()) : "") + ")V";
 		MethodNode defCtr = classNode.searchMethodByShortId(ctrId);
-		if (defCtr == null) {
+		if (defCtr == null || defCtr.equals(callMth) || defCtr.getAccessFlags().isSynthetic()) {
 			return null;
 		}
 		ConstructorInsn newInsn = new ConstructorInsn(defCtr.getMethodInfo(), co.getCallType());
-		newInsn.setResult(co.getResult());
+		newInsn.setResult(co.getResult().duplicate());
 		return newInsn;
 	}
 

jadx-core/src/test/java/jadx/tests/integration/others/TestSyntheticConstructor.java

+package jadx.tests.integration.others;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.tests.api.SmaliTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestSyntheticConstructor extends SmaliTest {
+	// @formatter:off
+	/*
+		public class Test {
+			static {
+				new BuggyConstructor();
+			}
+		}
+	*/
+	// @formatter:on
+
+	@Test
+	public void test() {
+		disableCompilation();
+		assertThat(getClassNodeFromSmaliFiles("Test"))
+				.code()
+				.containsLine(2, "new BuggyConstructor();");
+	}
+}

jadx-core/src/test/smali/others/TestSyntheticConstructor/BuggyConstructor.smali

+.class public LBuggyConstructor;
+.super Ljava/lang/Object;
+.source "BuggyConstructor.java"
+
+#.implements LInterfaceClass;
+
+.method public synthetic constructor <init>()V
+    .locals 0
+    invoke-direct {p0}, Ljava/lang/Object;-><init>()V
+    return-void
+.end method

jadx-core/src/test/smali/others/TestSyntheticConstructor/Test.smali

+.class public Lothers/Test;
+.super Ljava/lang/Object;
+.source "Test.java"
+
+.field public static final A00:Ljava/lang/Object;
+
+.method public static constructor <clinit>()V
+    .locals 1
+    new-instance v0, LBuggyConstructor;
+    invoke-direct {v0}, LBuggyConstructor;-><init>()V
+.end method