From 0112ce84a7830d772ccce640ed62200a90d08620 Mon Sep 17 00:00:00 2001
From: Osama Ansar <osama.ansar.pk@gmail.com>
Date: Mon, 12 Oct 2026 22:02:01 +0500
Subject: [PATCH] fix: do not continue a block quote paragraph from a
 whitespace-only line

In `> a\n>  \nb` the marker consumes one space and the remaining
whitespace-only text matched the lazy paragraph branch of the blockquote
rule, which then swallowed the following unquoted line into the quote.
A line with only whitespace after the marker is blank and must end the
paragraph, as for `>` and `> `.
---
 src/rules.ts                                         | 4 +++-
 test/specs/new/blockquote_whitespace_only_empty.html | 3 +++
 test/specs/new/blockquote_whitespace_only_empty.md   | 2 ++
 test/specs/new/blockquote_whitespace_only_line.html  | 8 ++++++++
 test/specs/new/blockquote_whitespace_only_line.md    | 7 +++++++
 5 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/specs/new/blockquote_whitespace_only_empty.html
 create mode 100644 test/specs/new/blockquote_whitespace_only_empty.md
 create mode 100644 test/specs/new/blockquote_whitespace_only_line.html
 create mode 100644 test/specs/new/blockquote_whitespace_only_line.md

diff --git a/src/rules.ts b/src/rules.ts
index 02e12330c8..2693902d16 100644
--- a/src/rules.ts
+++ b/src/rules.ts
@@ -190,7 +190,9 @@ const paragraph = createParagraph(/ {0,3}(?:[*+-]|1[.)])[ \t]+[^ \t\n]/);
 // paragraph, where an empty list cannot interrupt)
 const blockquoteParagraph = createParagraph(/ {0,3}(?:[*+-]|\d{1,9}[.)])(?:[ \t]|\n|$)/);
 
-const blockquote = edit(/^( {0,3}> ?(paragraph|[^\n]*)(?:\n|$))+/)
+// a line with only whitespace after the marker is blank, so it must not start a
+// paragraph that lazily continues onto the next line
+const blockquote = edit(/^( {0,3}> ?(?:(?![ \t]*(?:\n|$))(paragraph)|[^\n]*)(?:\n|$))+/)
   .replace('paragraph', blockquoteParagraph)
   .getRegex();
 
diff --git a/test/specs/new/blockquote_whitespace_only_empty.html b/test/specs/new/blockquote_whitespace_only_empty.html
new file mode 100644
index 0000000000..c630a798d4
--- /dev/null
+++ b/test/specs/new/blockquote_whitespace_only_empty.html
@@ -0,0 +1,3 @@
+<blockquote>
+</blockquote>
+<p>b</p>
diff --git a/test/specs/new/blockquote_whitespace_only_empty.md b/test/specs/new/blockquote_whitespace_only_empty.md
new file mode 100644
index 0000000000..c5d1e53afb
--- /dev/null
+++ b/test/specs/new/blockquote_whitespace_only_empty.md
@@ -0,0 +1,2 @@
+>  
+b
diff --git a/test/specs/new/blockquote_whitespace_only_line.html b/test/specs/new/blockquote_whitespace_only_line.html
new file mode 100644
index 0000000000..c88b315b86
--- /dev/null
+++ b/test/specs/new/blockquote_whitespace_only_line.html
@@ -0,0 +1,8 @@
+<blockquote>
+<p>a</p>
+</blockquote>
+<p>b</p>
+<blockquote>
+<p>c</p>
+</blockquote>
+<p>d</p>
diff --git a/test/specs/new/blockquote_whitespace_only_line.md b/test/specs/new/blockquote_whitespace_only_line.md
new file mode 100644
index 0000000000..fa3a72cb4c
--- /dev/null
+++ b/test/specs/new/blockquote_whitespace_only_line.md
@@ -0,0 +1,7 @@
+> a
+>  
+b
+
+> c
+>   
+d