fix: handle empty block at end of else-if chain (#1674)

jadx-core/src/main/java/jadx/core/dex/visitors/regions/IfRegionVisitor.java

@@ -3,8 +3,10 @@ package jadx.core.dex.visitors.regions;
 import java.util.List;
 
 import jadx.core.dex.attributes.AFlag;
+import jadx.core.dex.instructions.InsnType;
 import jadx.core.dex.nodes.IContainer;
 import jadx.core.dex.nodes.IRegion;
+import jadx.core.dex.nodes.InsnNode;
 import jadx.core.dex.nodes.MethodNode;
 import jadx.core.dex.regions.Region;
 import jadx.core.dex.regions.conditions.IfCondition;
@@ -45,7 +47,7 @@ public class IfRegionVisitor extends AbstractVisitor {
 		}
 	}
 
-	@SuppressWarnings("UnnecessaryReturnStatement")
+	@SuppressWarnings({ "UnnecessaryReturnStatement", "StatementWithEmptyBody" })
 	private static void orderBranches(MethodNode mth, IfRegion ifRegion) {
 		if (RegionUtils.isEmpty(ifRegion.getElseRegion())) {
 			return;
@@ -79,9 +81,15 @@ public class IfRegionVisitor extends AbstractVisitor {
 					return;
 				}
 			}
-			boolean lastRegion = ifRegion == RegionUtils.getLastRegion(mth.getRegion());
+			boolean lastRegion = RegionUtils.hasExitEdge(ifRegion);
 			if (elseSize == 1 && lastRegion && mth.isVoidReturn()) {
-				// single return at method end will be removed later
+				InsnNode lastElseInsn = RegionUtils.getLastInsn(ifRegion.getElseRegion());
+				if (lastElseInsn != null && lastElseInsn.getType() == InsnType.THROW) {
+					// move `throw` into `then` block
+					invertIfRegion(ifRegion);
+				} else {
+					// single return at method end will be removed later
+				}
 				return;
 			}
 			if (!lastRegion) {

jadx-core/src/main/java/jadx/core/utils/RegionUtils.java

@@ -146,20 +146,6 @@ public class RegionUtils {
 		}
 	}
 
-	@Nullable
-	public static IContainer getLastRegion(@Nullable IContainer container) {
-		if (container == null) {
-			return null;
-		}
-		if (container instanceof IBlock || container instanceof IBranchRegion) {
-			return container;
-		}
-		if (container instanceof IRegion) {
-			return getLastRegion(Utils.last(((IRegion) container).getSubBlocks()));
-		}
-		throw new JadxRuntimeException(unknownContainerType(container));
-	}
-
 	public static boolean isExitBlock(MethodNode mth, IContainer container) {
 		if (container instanceof BlockNode) {
 			return BlockUtils.isExitBlock(mth, (BlockNode) container);

jadx-core/src/test/java/jadx/tests/integration/conditions/TestElseIfCodeStyle.java

@@ -0,0 +1,37 @@
+package jadx.tests.integration.conditions;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.api.ICodeWriter;
+import jadx.tests.api.IntegrationTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestElseIfCodeStyle extends IntegrationTest {
+
+	@SuppressWarnings("unused")
+	public static class TestCls {
+
+		public void test(String str) {
+			if ("a".equals(str)) {
+				call(1);
+			} else if ("b".equals(str)) {
+				call(2);
+			} else if ("c".equals(str)) {
+				call(3);
+			}
+		}
+
+		private void call(int i) {
+		}
+	}
+
+	@Test
+	public void test() {
+		noDebugInfo();
+		assertThat(getClassNode(TestCls.class))
+				.code()
+				.doesNotContain("!\"c\".equals(str)")
+				.doesNotContain("{" + ICodeWriter.NL + indent(2) + "} else {"); // no empty `then` block
+	}
+}