From aa73711d67f0230b3cd5cc0b2c17a672d82f59dd Mon Sep 17 00:00:00 2001
From: Kevin Backhouse <kevinbackhouse@github.com>
Date: Mon, 6 Mar 2023 22:15:58 +0000
Subject: [PATCH] Early-terminate the loop in check_open_blocks when the
 current line is blank.

---
 src/blocks.c | 32 +++++++++++++++++++++++++++++---
 src/parser.h | 10 ++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/blocks.c b/src/blocks.c
index 63741594e..2c70b21c9 100644
--- a/src/blocks.c
+++ b/src/blocks.c
@@ -409,9 +409,11 @@ static cmark_node *finalize(cmark_parser *parser, cmark_node *b) {
 // in parser. (Used to check that the counts in parser, which are updated incrementally, are
 // correct.)
 bool check_open_block_counts(cmark_parser *parser) {
-  cmark_parser tmp_parser = {0}; // Only used for its open_block_counts field.
+  cmark_parser tmp_parser = {0}; // Only used for its open_block_counts and total_open_blocks fields.
   add_open_block_counts(&tmp_parser, parser->root);
-  return memcmp(tmp_parser.open_block_counts, parser->open_block_counts, sizeof(parser->open_block_counts)) == 0;
+  return
+    tmp_parser.total_open_blocks == parser->total_open_blocks &&
+    memcmp(tmp_parser.open_block_counts, parser->open_block_counts, sizeof(parser->open_block_counts)) == 0;
 }
 
 // Add a node as child of another.  Return pointer to child.
@@ -1082,10 +1084,14 @@ static cmark_node *check_open_blocks(cmark_parser *parser, cmark_chunk *input,
   *all_matched = false;
   cmark_node *container = parser->root;
   cmark_node_type cont_type;
+  cmark_parser tmp_parser; // Only used for its open_block_counts and total_open_blocks fields.
+  memcpy(tmp_parser.open_block_counts, parser->open_block_counts, sizeof(parser->open_block_counts));
+  tmp_parser.total_open_blocks = parser->total_open_blocks;
 
   assert(check_open_block_counts(parser));
 
   while (S_last_child_is_open(container)) {
+    decr_open_block_count(&tmp_parser, S_type(container));
     container = container->last_child;
     cont_type = S_type(container);
 
@@ -1097,6 +1103,26 @@ static cmark_node *check_open_blocks(cmark_parser *parser, cmark_chunk *input,
       continue;
     }
 
+    if (parser->blank) {
+      const size_t n_list = read_open_block_count(&tmp_parser, CMARK_NODE_LIST);
+      const size_t n_item = read_open_block_count(&tmp_parser, CMARK_NODE_ITEM);
+      const size_t n_para = read_open_block_count(&tmp_parser, CMARK_NODE_PARAGRAPH);
+      if (n_list + n_item + n_para == tmp_parser.total_open_blocks) {
+        if (parser->current->flags & CMARK_NODE__OPEN_BLOCK) {
+          if (S_type(parser->current) == CMARK_NODE_PARAGRAPH) {
+            container = parser->current;
+            goto done;
+          }
+          if (S_type(parser->current) == CMARK_NODE_ITEM) {
+            if (parser->current->flags & CMARK_NODE__OPEN) {
+              container = parser->current;
+              cont_type = S_type(container);
+            }
+          }
+        }
+      }
+    }
+
     switch (cont_type) {
     case CMARK_NODE_BLOCK_QUOTE:
       if (!parse_block_quote_prefix(parser, input))
@@ -1387,7 +1413,7 @@ static void add_text_to_container(cmark_parser *parser, cmark_node *container,
   S_set_last_line_blank(container, last_line_blank);
 
   tmp = container;
-  while (tmp->parent) {
+  while (tmp->parent && S_last_line_blank(tmp->parent)) {
     S_set_last_line_blank(tmp->parent, false);
     tmp = tmp->parent;
   }
diff --git a/src/parser.h b/src/parser.h
index 5020aa20b..05403fe3d 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -66,12 +66,14 @@ struct cmark_parser {
    * For example, CMARK_NODE_LIST (0x8003) is stored at offset 2.
    */
   size_t open_block_counts[CMARK_NODE_TYPE_BLOCK_LIMIT];
+  size_t total_open_blocks;
 };
 
 static CMARK_INLINE void incr_open_block_count(cmark_parser *parser, cmark_node_type type) {
   assert(type > CMARK_NODE_TYPE_BLOCK);
   assert(type <= CMARK_NODE_TYPE_BLOCK + CMARK_NODE_TYPE_BLOCK_LIMIT);
   parser->open_block_counts[type - CMARK_NODE_TYPE_BLOCK - 1]++;
+  parser->total_open_blocks++;
 }
 
 static CMARK_INLINE void decr_open_block_count(cmark_parser *parser, cmark_node_type type) {
@@ -79,6 +81,14 @@ static CMARK_INLINE void decr_open_block_count(cmark_parser *parser, cmark_node_
   assert(type <= CMARK_NODE_TYPE_BLOCK + CMARK_NODE_TYPE_BLOCK_LIMIT);
   assert(parser->open_block_counts[type - CMARK_NODE_TYPE_BLOCK - 1] > 0);
   parser->open_block_counts[type - CMARK_NODE_TYPE_BLOCK - 1]--;
+  assert(parser->total_open_blocks > 0);
+  parser->total_open_blocks--;
+}
+
+static CMARK_INLINE size_t read_open_block_count(cmark_parser *parser, cmark_node_type type) {
+  assert(type > CMARK_NODE_TYPE_BLOCK);
+  assert(type <= CMARK_NODE_TYPE_BLOCK + CMARK_NODE_TYPE_BLOCK_LIMIT);
+  return parser->open_block_counts[type - CMARK_NODE_TYPE_BLOCK - 1];
 }
 
 #ifdef __cplusplus