From c15c57a6af582e8d8433bc1b293b471743fe2dc0 Mon Sep 17 00:00:00 2001
From: Peter Elliott <pelliott@ualberta.ca>
Date: Sun, 24 Apr 2022 22:44:53 -0600
Subject: [PATCH] LibMarkdown: Make thematic break parsing more correct

also fix a conflict with lists and thematic breaks
---
 Userland/Libraries/LibMarkdown/ContainerBlock.cpp |  2 +-
 Userland/Libraries/LibMarkdown/HorizontalRule.cpp | 14 +++++---------
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/Userland/Libraries/LibMarkdown/ContainerBlock.cpp b/Userland/Libraries/LibMarkdown/ContainerBlock.cpp
index acb0f4db59..7d6223c09a 100644
--- a/Userland/Libraries/LibMarkdown/ContainerBlock.cpp
+++ b/Userland/Libraries/LibMarkdown/ContainerBlock.cpp
@@ -108,11 +108,11 @@ OwnPtr<ContainerBlock> ContainerBlock::parse(LineIterator& lines)
         }
 
         bool any = try_parse_block<Table>(lines, blocks)
+            || try_parse_block<HorizontalRule>(lines, blocks)
             || try_parse_block<List>(lines, blocks)
             || try_parse_block<CodeBlock>(lines, blocks)
             || try_parse_block<CommentBlock>(lines, blocks)
             || try_parse_block<Heading>(lines, blocks)
-            || try_parse_block<HorizontalRule>(lines, blocks)
             || try_parse_block<BlockQuote>(lines, blocks);
 
         if (any) {
diff --git a/Userland/Libraries/LibMarkdown/HorizontalRule.cpp b/Userland/Libraries/LibMarkdown/HorizontalRule.cpp
index d18a9a489a..7bb8edb42f 100644
--- a/Userland/Libraries/LibMarkdown/HorizontalRule.cpp
+++ b/Userland/Libraries/LibMarkdown/HorizontalRule.cpp
@@ -8,6 +8,7 @@
 #include <AK/StringBuilder.h>
 #include <LibMarkdown/HorizontalRule.h>
 #include <LibMarkdown/Visitor.h>
+#include <LibRegex/Regex.h>
 
 namespace Markdown {
 
@@ -34,6 +35,8 @@ RecursionDecision HorizontalRule::walk(Visitor& visitor) const
     return RecursionDecision::Continue;
 }
 
+static Regex<ECMA262> thematic_break_re("^ {0,3}([\\*\\-_])(\\s*\\1\\s*){2,}$");
+
 OwnPtr<HorizontalRule> HorizontalRule::parse(LineIterator& lines)
 {
     if (lines.is_end())
@@ -41,16 +44,9 @@ OwnPtr<HorizontalRule> HorizontalRule::parse(LineIterator& lines)
 
     StringView line = *lines;
 
-    if (line.length() < 3)
+    auto match = thematic_break_re.match(line);
+    if (!match.success)
         return {};
-    if (!line.starts_with('-') && !line.starts_with('_') && !line.starts_with('*'))
-        return {};
-
-    auto first_character = line.characters_without_null_termination()[0];
-    for (auto ch : line) {
-        if (ch != first_character)
-            return {};
-    }
 
     ++lines;
     return make<HorizontalRule>();