3 files changed, 34 insertions, 27 deletions

diff --git a/src/blocks.c b/src/blocks.c
index 58162b5..ab9f667 100644
--- a/src/blocks.c
+++ b/src/blocks.c
@@ -818,7 +818,7 @@ cmark_node *cmark_finish(cmark_doc_parser *parser)
 	finalize_document(parser);
 	strbuf_free(parser->curline);
 #if CMARK_DEBUG_NODES
-	if (cmark_node_check(parser->root)) {
+	if (cmark_node_check(parser->root, stderr)) {
 		abort();
 	}
 #endif
diff --git a/src/node.c b/src/node.c
index bb9cacc..a79dd82 100644
--- a/src/node.c
+++ b/src/node.c
@@ -558,58 +558,63 @@ cmark_node_append_child(cmark_node *node, cmark_node *child)
 }
 
 static void
-S_print_error(cmark_node *node, const char *elem)
+S_print_error(FILE *out, cmark_node *node, const char *elem)
 {
-	fprintf(stderr, "Invalid '%s' in node type %s at %d:%d\n", elem,
+	if (out == NULL) {
+		return;
+	}
+	fprintf(out, "Invalid '%s' in node type %s at %d:%d\n", elem,
 		S_type_string(node), node->start_line, node->start_column);
 }
 
 int
-cmark_node_check(cmark_node *node)
+cmark_node_check(cmark_node *node, FILE *out)
 {
-	cmark_node *cur = node;
+	cmark_node *cur;
 	int errors = 0;
 
-	while (cur) {
+	if (!node) {
+		return 0;
+	}
+
+	cur = node;
+	while (true) {
 		if (cur->first_child) {
 			if (cur->first_child->parent != cur) {
-				S_print_error(cur->first_child, "parent");
+				S_print_error(out, cur->first_child, "parent");
 				cur->first_child->parent = cur;
 				++errors;
 			}
 			cur = cur->first_child;
+			continue;
+		}
+
+	next_sibling:
+		if (cur == node) {
+			break;
 		}
-		else if (cur->next) {
+		if (cur->next) {
 			if (cur->next->prev != cur) {
-				S_print_error(cur->next, "prev");
+				S_print_error(out, cur->next, "prev");
 				cur->next->prev = cur;
 				++errors;
 			}
 			if (cur->next->parent != cur->parent) {
-				S_print_error(cur->next, "parent");
+				S_print_error(out, cur->next, "parent");
 				cur->next->parent = cur->parent;
 				++errors;
 			}
 			cur = cur->next;
+			continue;
 		}
-		else {
-			if (cur->parent->last_child != cur) {
-				S_print_error(cur->parent, "last_child");
-				cur->parent->last_child = cur;
-				++errors;
-			}
 
-			cmark_node *ancestor = cur->parent;
-			cur = NULL;
-
-			while (ancestor != node->parent) {
-				if (ancestor->next) {
-					cur = ancestor->next;
-					break;
-				}
-				ancestor = ancestor->parent;
-			}
+		if (cur->parent->last_child != cur) {
+			S_print_error(out, cur->parent, "last_child");
+			cur->parent->last_child = cur;
+			++errors;
 		}
+		cur = cur->parent;
+		goto next_sibling;
 	}
 
 	return errors;
diff --git a/src/node.h b/src/node.h
index 2d7f0a1..d1245a5 100644
--- a/src/node.h
+++ b/src/node.h
@@ -5,6 +5,8 @@
 extern "C" {
 #endif
 
+#include <stdio.h>
+
 #include "cmark.h"
 #include "buffer.h"
 #include "chunk.h"
@@ -62,7 +64,7 @@ struct cmark_node {
 };
 
 CMARK_EXPORT int
-cmark_node_check(cmark_node *node);
+cmark_node_check(cmark_node *node, FILE *out);
 
 #ifdef __cplusplus
 }