Fix quadratic performance issue in list numbering

src/commonmark.c

@@ -153,7 +153,6 @@ static bool is_autolink(cmark_node *node) {
 
 static int S_render_node(cmark_renderer *renderer, cmark_node *node,
                          cmark_event_type ev_type, int options) {
-  cmark_node *tmp;
   int list_number;
   cmark_delim_type list_delim;
   size_t numticks;
@@ -216,13 +215,8 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     if (cmark_node_get_list_type(node->parent) == CMARK_BULLET_LIST) {
       marker_width = 4;
     } else {
-      list_number = cmark_node_get_list_start(node->parent);
+      list_number = cmark_node_get_item_index(node);
       list_delim = cmark_node_get_list_delim(node->parent);
-      tmp = node;
-      while (tmp->prev) {
-        tmp = tmp->prev;
-        list_number += 1;
-      }
       // we ensure a width of at least 4 so
       // we get nice transition from single digits
       // to double

src/man.c

@@ -72,7 +72,6 @@ static void S_outc(cmark_renderer *renderer, cmark_escaping escape, int32_t c,
 
 static int S_render_node(cmark_renderer *renderer, cmark_node *node,
                          cmark_event_type ev_type, int options) {
-  cmark_node *tmp;
   int list_number;
   bool entering = (ev_type == CMARK_EVENT_ENTER);
   bool allow_wrap = renderer->width > 0 && !(CMARK_OPT_NOBREAKS & options);
@@ -125,12 +124,7 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
       if (cmark_node_get_list_type(node->parent) == CMARK_BULLET_LIST) {
         LIT("\\[bu] 2");
       } else {
-        list_number = cmark_node_get_list_start(node->parent);
-        tmp = node;
-        while (tmp->prev) {
-          tmp = tmp->prev;
-          list_number += 1;
-        }
+        list_number = cmark_node_get_item_index(node);
         char list_number_s[LIST_NUMBER_SIZE];
         snprintf(list_number_s, LIST_NUMBER_SIZE, "\"%d.\" 4", list_number);
         LIT(list_number_s);

src/node.c

@@ -466,6 +466,31 @@ int cmark_node_set_list_tight(cmark_node *node, int tight) {
   }
 }
 
+int cmark_node_get_item_index(cmark_node *node) {
+  if (node == NULL) {
+    return 0;
+  }
+
+  if (node->type == CMARK_NODE_ITEM) {
+    return node->as.list.start;
+  } else {
+    return 0;
+  }
+}
+
+int cmark_node_set_item_index(cmark_node *node, int idx) {
+  if (node == NULL || idx < 0) {
+    return 0;
+  }
+
+  if (node->type == CMARK_NODE_ITEM) {
+    node->as.list.start = idx;
+    return 1;
+  } else {
+    return 0;
+  }
+}
+
 const char *cmark_node_get_fence_info(cmark_node *node) {
   if (node == NULL) {
     return NULL;

src/node.h

@@ -85,6 +85,17 @@ struct cmark_node {
 
 CMARK_EXPORT int cmark_node_check(cmark_node *node, FILE *out);
 
+/**
+ * Returns item index of 'node'. This is only used when rendering output
+ * formats such as commonmark, which need to output the index. It is not
+ * required for formats such as html or latex.
+ */
+int cmark_node_get_item_index(cmark_node *node);
+
+/** Sets item index of 'node'. Returns 1 on success, 0 on failure.
+ */
+int cmark_node_set_item_index(cmark_node *node, int idx);
+
 #ifdef __cplusplus
 }
 #endif

src/render.c

@@ -170,6 +170,15 @@ char *cmark_render(cmark_node *root, int options, int width,
 
   while ((ev_type = cmark_iter_next(iter)) != CMARK_EVENT_DONE) {
     cur = cmark_iter_get_node(iter);
+    if (cur->type == CMARK_NODE_ITEM) {
+      // Calculate the list item's index, for the benefit of output formats
+      // like commonmark and plaintext.
+      if (cur->prev) {
+        cmark_node_set_item_index(cur, 1 + cmark_node_get_item_index(cur->prev));
+      } else {
+        cmark_node_set_item_index(cur, cmark_node_get_list_start(cur->parent));
+      }
+    }
     if (!render_node(&renderer, cur, ev_type, options)) {
       // a false value causes us to skip processing
       // the node's contents.  this is used for