From 85a66ba052cef1cfc164aa286840788e82c8aab1 Mon Sep 17 00:00:00 2001
From: Yuzhong Zhang <BetterAndBetterII@users.noreply.github.com>
Date: Sun, 30 Aug 2026 02:01:20 +0000
Subject: [PATCH] fix: escape leading tilde fences after wrap

Wrapping can move ~~~ to column 0, which CommonMark treats as a
fenced code opener. Escape a leading run of three or more tildes
in paragraph() like the other line-start guards.

Fixes #590
---
 src/mdformat/renderer/_context.py |  5 +++++
 tests/data/wrap_width_50.md       | 30 ++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/src/mdformat/renderer/_context.py b/src/mdformat/renderer/_context.py
index 238dd07d..c38315f5 100644
--- a/src/mdformat/renderer/_context.py
+++ b/src/mdformat/renderer/_context.py
@@ -459,6 +459,11 @@ def paragraph(node: RenderTreeNode, context: RenderContext) -> str:  # noqa: C90
         elif all(c == "=" for c in stripped):
             lines[i] = lines[i].replace("=", "\\=", 1)
 
+        # Make sure a paragraph line does not start with three or more
+        # tildes (otherwise it will be interpreted as a fenced code block).
+        if re.match(r"~{3,}", lines[i]):
+            lines[i] = f"\\{lines[i]}"
+
         # Check if the line could be interpreted as an HTML block.
         # If yes, prefix it with 4 spaces to prevent this.
         for html_seq_tuple in HTML_SEQUENCES:
diff --git a/tests/data/wrap_width_50.md b/tests/data/wrap_width_50.md
index eceede9f..be9fa55c 100644
--- a/tests/data/wrap_width_50.md
+++ b/tests/data/wrap_width_50.md
@@ -188,3 +188,33 @@ Starts with encoded space
 .
 &#32;* * \*
 .
+
+
+Wrap three tildes to line start (issue #590)
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA ~~~ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+\~~~
+BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.
+
+
+Wrap two tildes to line start
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA ~~ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+~~
+BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.
+
+
+Wrap four tildes to line start
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA ~~~~ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+\~~~~
+BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
+.