From 1428013d52e87528e01503cc6cf37c74614a8c7d Mon Sep 17 00:00:00 2001
From: Noir <160358296+afifm561@users.noreply.github.com>
Date: Mon, 12 Oct 2026 23:02:21 +0000
Subject: [PATCH] Don't leave an empty paragraph before a setext underline
 (#262)

When a paragraph contains only link reference definitions and is
followed by a setext heading underline, the setext block start stripped
the definitions from the paragraph before deciding not to create a
heading. The emptied paragraph was then skipped by
removeLinkReferenceDefinitions and rendered as <p></p>.

Parse the definitions on a copy of the paragraph content, so the
paragraph is only changed when it actually becomes a heading.
---
 lib/blocks.js       | 19 ++++++++-----------
 test/regression.txt | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/lib/blocks.js b/lib/blocks.js
index c74a278b..b3c5b8a0 100644
--- a/lib/blocks.js
+++ b/lib/blocks.js
@@ -607,23 +607,20 @@ var blockStarts = [
                 .match(reSetextHeadingLine))
         ) {
             parser.closeUnmatchedBlocks();
-            // resolve reference link definitiosn
+            // resolve reference link definitions on a copy, so the paragraph
+            // is left untouched if this turns out not to be a heading (#262)
             var pos;
+            var content = container._string_content;
             while (
-                peek(container._string_content, 0) === C_OPEN_BRACKET &&
-                (pos = parser.inlineParser.parseReference(
-                    container._string_content,
-                    parser.refmap
-                ))
+                peek(content, 0) === C_OPEN_BRACKET &&
+                (pos = parser.inlineParser.parseReference(content, parser.refmap))
             ) {
-                container._string_content = container._string_content.slice(
-                    pos
-                );
+                content = content.slice(pos);
             }
-            if (container._string_content.length > 0) {
+            if (content.length > 0) {
                 var heading = new Node("heading", container.sourcepos);
                 heading.level = match[0][0] === "=" ? 1 : 2;
-                heading._string_content = container._string_content;
+                heading._string_content = content;
                 container.insertAfter(heading);
                 container.unlink();
                 parser.tip = heading;
diff --git a/test/regression.txt b/test/regression.txt
index 46b5e6bb..369d921e 100644
--- a/test/regression.txt
+++ b/test/regression.txt
@@ -665,3 +665,42 @@ Entities inside autolinks (#263).
 <pre><code class="language-js"></code></pre>
 <pre><code class="language-js"></code></pre>
 ````````````````````````````````
+
+Issue #262 - link reference definition followed by a setext underline
+must not leave an empty paragraph behind.
+
+```````````````````````````````` example
+[a]: b
+---
+.
+<hr />
+````````````````````````````````
+
+```````````````````````````````` example
+[a]: b
+===
+.
+<p>===</p>
+````````````````````````````````
+
+```````````````````````````````` example
+[a]: b
+---
+
+[a]: b
+===
+.
+<hr />
+<p>===</p>
+````````````````````````````````
+
+```````````````````````````````` example
+[a]: b
+Foo
+---
+
+[a]
+.
+<h2>Foo</h2>
+<p><a href="b">a</a></p>
+````````````````````````````````