From 7f2f7f8dff99fb1df3d23eddb604298d9f8951d8 Mon Sep 17 00:00:00 2001
From: zayeem shaikh <zayeem@bugqore.com>
Date: Tue, 13 Oct 2026 23:53:37 +0530
Subject: [PATCH] fix hard line break round-trip in commonmark renderer

---
 api_test/main.c  | 31 +++++++++++++++++++++++++++++++
 src/commonmark.c |  6 +++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/api_test/main.c b/api_test/main.c
index 877d72e9f..0df1a7d8d 100644
--- a/api_test/main.c
+++ b/api_test/main.c
@@ -773,6 +773,37 @@ static void render_commonmark(test_batch_runner *runner) {
   free(commonmark);
 
   cmark_node_free(empty_item_doc);
+
+  // Hard line breaks are written as a backslash break in every position.
+  // Two trailing spaces would be stripped as insignificant whitespace at the
+  // start of a line, or after a space, losing the break on a round trip.
+  static const char lead_break[] = "\\\nfoo\n";
+  cmark_node *lead_break_doc =
+      cmark_parse_document(lead_break, sizeof(lead_break) - 1, CMARK_OPT_DEFAULT);
+  commonmark = cmark_render_commonmark(lead_break_doc, CMARK_OPT_DEFAULT, 0);
+  STR_EQ(runner, commonmark, "\\\nfoo\n",
+         "render hard break at start of line");
+  free(commonmark);
+  cmark_node_free(lead_break_doc);
+
+  static const char space_break[] = "foo \\\nbar\n";
+  cmark_node *space_break_doc =
+      cmark_parse_document(space_break, sizeof(space_break) - 1, CMARK_OPT_DEFAULT);
+  commonmark = cmark_render_commonmark(space_break_doc, CMARK_OPT_DEFAULT, 0);
+  STR_EQ(runner, commonmark, "foo \\\nbar\n",
+         "render hard break after a space");
+  free(commonmark);
+  cmark_node_free(space_break_doc);
+
+  static const char plain_break[] = "foo\\\nbar\n";
+  cmark_node *plain_break_doc =
+      cmark_parse_document(plain_break, sizeof(plain_break) - 1, CMARK_OPT_DEFAULT);
+  commonmark = cmark_render_commonmark(plain_break_doc, CMARK_OPT_DEFAULT, 0);
+  STR_EQ(runner, commonmark, "foo\\\nbar\n",
+         "render ordinary hard break");
+  free(commonmark);
+  cmark_node_free(plain_break_doc);
+
   cmark_node_free(text);
   cmark_node_free(doc);
 }
diff --git a/src/commonmark.c b/src/commonmark.c
index 8a2bc5184..44ee695d2 100644
--- a/src/commonmark.c
+++ b/src/commonmark.c
@@ -331,7 +331,11 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
 
   case CMARK_NODE_LINEBREAK:
     if (!(CMARK_OPT_HARDBREAKS & options)) {
-      LIT("  ");
+      // A backslash line break is unambiguous in every position. Two trailing
+      // spaces are only recognized as a hard break when they follow text on
+      // the line; at the start of a line, or after a space, they are stripped
+      // as insignificant whitespace and the break is lost on a round trip.
+      LIT("\\");
     }
     CR();
     break;