From 0faa62be9fc7a0cfb78afabd44808c32ff682dfc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonatan=20M=C3=A4nnchen?= <jonatan@maennchen.ch>
Date: Mon, 25 May 2026 23:44:16 +0200
Subject: [PATCH] Fix inline HTML comments being mishandled when inside
 backtick spans
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The line scanner's `process_line` function used a regex to split any line
containing `<!-- ... -->` into a block-level comment and trailing text,
even when the comment appeared inside a backtick code span. This caused
the backticks to be left unclosed and the comment to leak into the output.

Fix by removing `process_line` and the `comment_rest` regex entirely —
block-level comments at the start of a line are already handled correctly
by `html_comment_complete`/`html_comment_start` in `_type_of`. Add a new
`converter_for_inline_comment` to the inline parser so that `<!-- ... -->`
appearing inline in text is emitted as a proper comment node rather than
being HTML-escaped.

Closes #518
---
 lib/earmark_parser/ast/inline.ex                 | 12 ++++++++++++
 lib/earmark_parser/line_scanner.ex               | 14 +-------------
 .../i518_html_comment_in_backticks_test.exs      | 16 ++++++++++++++++
 3 files changed, 29 insertions(+), 13 deletions(-)
 create mode 100644 test/regressions/i518_html_comment_in_backticks_test.exs

diff --git a/lib/earmark_parser/ast/inline.ex b/lib/earmark_parser/ast/inline.ex
index a45287ea..750253a6 100644
--- a/lib/earmark_parser/ast/inline.ex
+++ b/lib/earmark_parser/ast/inline.ex
@@ -55,6 +55,7 @@ defmodule Earmark.Parser.Ast.Inline do
       converter_for_sup: &converter_for_sup/1,
       #
       converter_for_code: &converter_for_code/1,
+      converter_for_inline_comment: &converter_for_inline_comment/1,
       converter_for_br: &converter_for_br/1,
       converter_for_inline_ial: &converter_for_inline_ial/1,
       converter_for_pure_link: &converter_for_pure_link/1,
@@ -260,6 +261,17 @@ defmodule Earmark.Parser.Ast.Inline do
     end
   end
 
+  def converter_for_inline_comment({src, lnb, context, use_linky?}) do
+    comment_rgx = ~r/\A(<!--.*?-->)/s
+
+    if match = Regex.run(comment_rgx, src) do
+      [match, content] = match
+      inner = content |> String.replace_prefix("<!--", "") |> String.replace_suffix("-->", "")
+      out = {:comment, [], [inner], %{comment: true}}
+      {behead(src, match), lnb, prepend(context, out), use_linky?}
+    end
+  end
+
   def converter_for_inline_ial({src, lnb, context, use_linky?}) do
     inline_ial = ~r<^\s*\{:\s*(.*?)\s*}>
 
diff --git a/lib/earmark_parser/line_scanner.ex b/lib/earmark_parser/line_scanner.ex
index addb5ad8..990f1c23 100644
--- a/lib/earmark_parser/line_scanner.ex
+++ b/lib/earmark_parser/line_scanner.ex
@@ -42,7 +42,6 @@ defmodule Earmark.Parser.LineScanner do
   # Converted rgx_map to a function
   defp rgx_map(:block_quote), do: ~r/\A>\s?(.*)/
   defp rgx_map(:column_rgx), do: ~r{\A[\s|:-]+\z}
-  defp rgx_map(:comment_rest), do: ~r/(<!--.*?-->)(.*)/
   defp rgx_map(:fence), do: ~r/\A(\s*)(`{3,}|~{3,})\s*([^`\s]*)\s*\z/u
   defp rgx_map(:footnote_definition), do: ~r/\A\[\^([^\s\]]+)\]:\s+(.*)/
   defp rgx_map(:heading), do: ~r/^(\#{1,6})\s+(?|(.*?)\s*#*\s*$|(.*))/u
@@ -296,23 +295,12 @@ defmodule Earmark.Parser.LineScanner do
   end
 
   defp _with_lookahead([line_lnb | lines], options, recursive) do
-    process_line(line_lnb, options, recursive) ++
+    [type_of(line_lnb, options, recursive)] ++
       _with_lookahead(lines, options, recursive)
   end
 
   defp _with_lookahead([], _options, _recursive), do: []
 
-  defp process_line({line, lnb}, options, recursive) do
-    case regex_run(:comment_rest, line, capture: :all_but_first) do
-      [comment, rest] ->
-        [type_of({comment, lnb}, options, recursive)] ++
-          [type_of({rest, lnb}, options, recursive)]
-
-      nil ->
-        [type_of({line, lnb}, options, recursive)]
-    end
-  end
-
   defp _determine_if_header(columns) do
     columns
     |> Enum.all?(fn col -> regex_run(:column_rgx, col) end)
diff --git a/test/regressions/i518_html_comment_in_backticks_test.exs b/test/regressions/i518_html_comment_in_backticks_test.exs
new file mode 100644
index 00000000..83c35683
--- /dev/null
+++ b/test/regressions/i518_html_comment_in_backticks_test.exs
@@ -0,0 +1,16 @@
+defmodule Test.Regressions.I518HtmlCommentInBackticksTest do
+  use ExUnit.Case
+
+  test "HTML comment inside backticks is rendered as inline code" do
+    md = "some source `<!-- 2 -->`"
+    html = "<p>\nsome source <code class=\"inline\">&lt;!-- 2 --&gt;</code></p>\n"
+    assert Earmark.as_html(md) == {:ok, html, []}
+  end
+
+  test "HTML comment mid-line is rendered as a comment" do
+    md = "text <!-- comment --> more text"
+    html = "<p>\ntext <!-- comment -->\n more text</p>\n"
+    assert Earmark.as_html(md) == {:ok, html, []}
+  end
+end
+# SPDX-License-Identifier: Apache-2.0