fix: regression of handling of rule file in treesitter-ng.

gen.treesitter-ng/src/main/java/com/github/gumtreediff/gen/treesitterng/AbstractTreeSitterNgGenerator.java

@@ -161,10 +161,11 @@ protected static Pair<Tree, Boolean> tsNode2GumTree(
                 return null;
             }
         }
+        boolean ignoreLabel = false;
         if (currentRule.containsKey(YAML_LABEL_IGNORED)) {
             List<String> ignores = (List<String>) currentRule.get(YAML_LABEL_IGNORED);
             if (matchNodeOrAncestorTypes(ignores, node) != null) {
-                return null;
+                ignoreLabel = true;
             }
         }
         if (currentRule.containsKey(YAML_ALIASED)) {
@@ -182,9 +183,11 @@ protected static Pair<Tree, Boolean> tsNode2GumTree(
             }
         }
         Tree tree;
-        if (node.getChildCount() == 0) {
+        // attach label for non ignore-label leafs or flattened nodes
+        if ((node.getChildCount() == 0 && !ignoreLabel) || flatten) {
             tree = context.createTree(TypeSet.type(type), label);
-        } else {
+        }
+        else {
             tree = context.createTree(TypeSet.type(type));
         }
         tree.setPos(calculateOffset(contentLines, node.getStartPoint()));
@@ -209,7 +212,7 @@ private static TreeContext generateFromTreeSitterTree(
         while (!tsNodeStack.isEmpty()) {
             TSNode tsNodeNow = tsNodeStack.pop();
             Pair<Tree, Boolean> treeNow = treeStack.pop();
-            // flatten here
+            // if node was flattened, ignore children
             if (treeNow.second) {
                 continue;
             }

gen.treesitter-ng/src/test/java/com/github/gumtreediff/gen/treesitterng/PythonTreeSitterNgTreeGeneratorTest.java

@@ -0,0 +1,39 @@
+/*
+ * This file is part of GumTree.
+ *
+ * GumTree is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GumTree is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with GumTree. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2022 Jean-Rémy Falleri <jr.falleri@gmail.com>
+ */
+package com.github.gumtreediff.gen.treesitterng;
+
+import com.github.gumtreediff.tree.Tree;
+import com.github.gumtreediff.tree.TreeContext;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class PythonTreeSitterNgTreeGeneratorTest {
+    private final PythonTreeSitterNgTreeGenerator generator = new PythonTreeSitterNgTreeGenerator();
+
+    @Test
+    public void testString() throws IOException {
+        TreeContext src = generator.generateFrom().file("testData/python/foo.py");
+        assertEquals(12, src.getRoot().getMetrics().size);
+    }
+
+}

gen.treesitter-ng/testData/python/foo.py

@@ -0,0 +1,4 @@
+print("foo")
+
+def bar(i):
+    return