fix: don't end HTML comment blocks on a blank line (#1155)

HTML blocks of types 1-5 (e.g. `<!--` comments) must continue until
their closing sequence (`-->` for comments), per CommonMark. Only
types 6 and 7 end on a blank line.

The block scanner broke out of the continuation loop whenever a line
was outdented below the current block indent. Inside a container such
as a list item, a blank line is outdented (its sCount is 0), so a
comment block was terminated early instead of running to `-->`.

Skip that break for outdented blank lines unless the block type
actually ends on a blank line, so comment blocks no longer depend on
indentation. Adds regression fixtures for issue #1144.

Co-authored-by: ATOM00blue <219721791+ATOM00blue@users.noreply.github.com>

lib/rules_block/html_block.mjs

@@ -42,11 +42,22 @@ export default function html_block (state, startLine, endLine, silent) {
 
   let nextLine = startLine + 1
 
+  // Block types 6 and 7 (the only ones whose end condition is a blank line)
+  // have `/^$/` as their closing regexp. For all other types (1-5, e.g.
+  // `<!--` comments), a blank line is regular content and must not terminate
+  // the block - it ends only when its closing sequence is found.
+  const endsOnBlankLine = HTML_SEQUENCES[i][1].test('')
+
   // If we are here - we detected HTML block.
   // Let's roll down till block end.
   if (!HTML_SEQUENCES[i][1].test(lineText)) {
     for (; nextLine < endLine; nextLine++) {
-      if (state.sCount[nextLine] < state.blkIndent) { break }
+      if (state.sCount[nextLine] < state.blkIndent) {
+        // An outdented blank line shouldn't end a block that doesn't end on a
+        // blank line (e.g. a `<!--` comment inside a list item). Such blocks
+        // must continue until their closing sequence regardless of indent.
+        if (endsOnBlankLine || !state.isEmpty(nextLine)) { break }
+      }
 
       pos = state.bMarks[nextLine] + state.tShift[nextLine]
       max = state.eMarks[nextLine]

test/fixtures/markdown-it/commonmark_extras.txt

@@ -791,3 +791,46 @@ a*a𐬼*a
 <p>a*𐬼a*a</p>
 <p>a*a𐬼*a</p>
 .
+
+Issue #1144. Comment HTML block (type 2) must not end on a blank line inside a list
+.
+1. item
+
+    <!--
+    a
+
+    b
+    -->
+    c
+.
+<ol>
+<li>
+<p>item</p>
+ <!--
+ a
+
+ b
+ -->
+<p>c</p>
+</li>
+</ol>
+.
+
+Issue #1144. Comment HTML block spanning a blank line inside a blockquote
+.
+> <!--
+> a
+>
+> b
+> -->
+> c
+.
+<blockquote>
+<!--
+a
+
+b
+-->
+<p>c</p>
+</blockquote>
+.