fix: check class name collisions (#1526)

jadx-core/src/main/java/jadx/core/codegen/ClassGen.java

@@ -614,21 +614,23 @@ private String useClassInternal(ClassInfo useCls, ClassInfo extClsInfo) {
 		if (useCls.equals(extClsInfo)) {
 			return shortName;
 		}
-		if (extClsInfo.getPackage().equals("java.lang") && extClsInfo.getParentClass() == null) {
-			return shortName;
-		}
 		if (isClassInnerFor(useCls, extClsInfo)) {
 			return shortName;
 		}
 		if (extClsInfo.isInner()) {
 			return expandInnerClassName(useCls, extClsInfo);
 		}
-		if (searchCollision(cls.root(), useCls, extClsInfo)) {
+		if (checkInnerCollision(cls.root(), useCls, extClsInfo)
+				|| checkInPackageCollision(cls.root(), useCls, extClsInfo)) {
 			return fullName;
 		}
 		if (isBothClassesInOneTopClass(useCls, extClsInfo)) {
 			return shortName;
 		}
+		// don't add import for top classes from 'java.lang' package (subpackages excluded)
+		if (extClsInfo.getPackage().equals("java.lang") && extClsInfo.getParentClass() == null) {
+			return shortName;
+		}
 		// don't add import if this class from same package
 		if (extClsInfo.getPackage().equals(useCls.getPackage()) && !extClsInfo.isInner()) {
 			return shortName;
@@ -709,7 +711,7 @@ private static boolean isClassInnerFor(ClassInfo inner, ClassInfo parent) {
 		return false;
 	}
 
-	private static boolean searchCollision(RootNode root, ClassInfo useCls, ClassInfo searchCls) {
+	private static boolean checkInnerCollision(RootNode root, @Nullable ClassInfo useCls, ClassInfo searchCls) {
 		if (useCls == null) {
 			return false;
 		}
@@ -726,7 +728,20 @@ private static boolean searchCollision(RootNode root, ClassInfo useCls, ClassInf
 				}
 			}
 		}
-		return searchCollision(root, useCls.getParentClass(), searchCls);
+		return checkInnerCollision(root, useCls.getParentClass(), searchCls);
+	}
+
+	/**
+	 * Check if class with same name exists in current package
+	 */
+	private static boolean checkInPackageCollision(RootNode root, ClassInfo useCls, ClassInfo searchCls) {
+		String currentPkg = useCls.getAliasPkg();
+		if (currentPkg.equals(searchCls.getAliasPkg())) {
+			// search class already from current package
+			return false;
+		}
+		String shortName = searchCls.getAliasShortName();
+		return root.getClsp().isClsKnown(currentPkg + '.' + shortName);
 	}
 
 	private void insertRenameInfo(ICodeWriter code, ClassNode cls) {

jadx-core/src/test/java/jadx/tests/integration/names/TestCollisionWithJavaLangClasses.java

@@ -0,0 +1,59 @@
+package jadx.tests.integration.names;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.core.dex.nodes.ClassNode;
+import jadx.tests.api.IntegrationTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestCollisionWithJavaLangClasses extends IntegrationTest {
+
+	public static class TestCls1 {
+		public static class System {
+			public static void main(String[] args) {
+				java.lang.System.out.println("Hello world");
+			}
+		}
+	}
+
+	@Test
+	public void test1() {
+		assertThat(getClassNode(TestCls1.class))
+				.code()
+				.containsOne("java.lang.System.out.println");
+	}
+
+	public static class TestCls2 {
+		public void doSomething() {
+			System.doSomething();
+			java.lang.System.out.println("Hello World");
+		}
+
+		public static class System {
+			public static void doSomething() {
+			}
+		}
+	}
+
+	@Test
+	public void test2() {
+		assertThat(getClassNode(TestCls2.class))
+				.code()
+				.containsLine(2, "System.doSomething();")
+				.containsOne("java.lang.System.out.println");
+	}
+
+	@Test
+	public void test3() {
+		List<ClassNode> classes = getClassNodes(
+				jadx.tests.integration.names.pkg2.System.class,
+				jadx.tests.integration.names.pkg2.TestCls.class);
+		assertThat(searchCls(classes, "TestCls"))
+				.code()
+				.containsLine(2, "System.doSomething();")
+				.containsOne("java.lang.System.out.println");
+	}
+}

jadx-core/src/test/java/jadx/tests/integration/names/pkg2/System.java

@@ -0,0 +1,6 @@
+package jadx.tests.integration.names.pkg2;
+
+public class System {
+	public static void doSomething() {
+	}
+}

jadx-core/src/test/java/jadx/tests/integration/names/pkg2/TestCls.java

@@ -0,0 +1,8 @@
+package jadx.tests.integration.names.pkg2;
+
+public class TestCls {
+	public void doSomething() {
+		System.doSomething();
+		java.lang.System.out.println("Hello World");
+	}
+}