fix: handle methods with all NOPs (#744)

jadx-core/src/main/java/jadx/core/dex/attributes/AFlag.java

 package jadx.core.dex.attributes;
 
 public enum AFlag {
+	MTH_ENTER_BLOCK,
 	TRY_ENTER,
 	TRY_LEAVE,
 

jadx-core/src/main/java/jadx/core/dex/visitors/blocksmaker/BlockProcessor.java

@@ -39,7 +39,7 @@ public class BlockProcessor extends AbstractVisitor {
 
 	@Override
 	public void visit(MethodNode mth) {
-		if (mth.isNoCode()) {
+		if (mth.isNoCode() || mth.getBasicBlocks().isEmpty()) {
 			return;
 		}
 		processBlocksTree(mth);

jadx-core/src/main/java/jadx/core/dex/visitors/blocksmaker/BlockSplitter.java

@@ -77,6 +77,7 @@ public class BlockSplitter extends AbstractVisitor {
 		InsnNode prevInsn = null;
 		Map<Integer, BlockNode> blocksMap = new HashMap<>();
 		BlockNode curBlock = startNewBlock(mth, 0);
+		curBlock.add(AFlag.MTH_ENTER_BLOCK);
 		mth.setEnterBlock(curBlock);
 
 		// split into blocks
@@ -331,7 +332,8 @@ public class BlockSplitter extends AbstractVisitor {
 	static boolean removeEmptyDetachedBlocks(MethodNode mth) {
 		return mth.getBasicBlocks().removeIf(block -> block.getInstructions().isEmpty()
 				&& block.getPredecessors().isEmpty()
-				&& block.getSuccessors().isEmpty());
+				&& block.getSuccessors().isEmpty()
+				&& !block.contains(AFlag.MTH_ENTER_BLOCK));
 	}
 
 	private static boolean removeUnreachableBlocks(MethodNode mth) {
@@ -385,7 +387,8 @@ public class BlockSplitter extends AbstractVisitor {
 		return block.getInstructions().isEmpty()
 				&& block.isAttrStorageEmpty()
 				&& block.getSuccessors().size() <= 1
-				&& !block.getPredecessors().isEmpty();
+				&& !block.getPredecessors().isEmpty()
+				&& !block.contains(AFlag.MTH_ENTER_BLOCK);
 	}
 
 	private static void collectSuccessors(BlockNode startBlock, Set<BlockNode> toRemove) {

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

@@ -39,7 +39,7 @@ public class RegionMakerVisitor extends AbstractVisitor {
 
 	@Override
 	public void visit(MethodNode mth) throws JadxException {
-		if (mth.isNoCode()) {
+		if (mth.isNoCode() || mth.getBasicBlocks().isEmpty()) {
 			return;
 		}
 		RegionMaker rm = new RegionMaker(mth);

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

+package jadx.tests.integration.others;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.core.dex.nodes.ClassNode;
+import jadx.tests.api.SmaliTest;
+
+import static jadx.tests.api.utils.JadxMatchers.containsLines;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class TestAllNops extends SmaliTest {
+
+	@Test
+	public void test() {
+		disableCompilation();
+		ClassNode cls = getClassNodeFromSmali();
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsLines(1, "private boolean test() {", "}"));
+		assertThat(code, containsLines(1, "private boolean testWithTryCatch() {", "}"));
+	}
+}

jadx-core/src/test/smali/others/TestAllNops.smali

+.class public Lothers/TestAllNops;
+.super Ljava/lang/Object;
+
+.method public constructor <init>()V
+    .registers 1
+
+    .line 55
+    nop
+
+    nop
+
+    nop
+
+    nop
+.end method
+
+.method private test()Z
+    .registers 11
+
+    .line 1480
+    nop
+
+    nop
+
+    .line 1481
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    .line 1485
+    nop
+
+    nop
+
+    .line 1486
+    nop
+
+    nop
+
+    .line 1487
+    nop
+
+.end method
+
+.method private testWithTryCatch()Z
+    .registers 11
+
+    .line 1480
+    :try_start_0
+    nop
+    nop
+
+    .line 1481
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    nop
+
+    .line 1485
+    nop
+
+    nop
+
+    :try_end_35
+    .catch Ljava/security/NoSuchAlgorithmException; {:try_start_0 .. :try_end_35} :catch_36
+
+    nop
+
+    .line 1547
+    :catch_36
+
+    nop
+
+    .line 1487
+    nop
+
+.end method