From 746e6e059f0d6897431e5339567d18789093d0c9 Mon Sep 17 00:00:00 2001
From: ll3006 <doublel3006@gmail.com>
Date: Wed, 8 Oct 2025 00:07:40 +0200
Subject: [PATCH] fix: inline parsing edge case with nested emphasis

before this, parsing would differ from CommonMark reference
implementation, giving '<p>**a_{b}**</p>' for '**a_{b}**'.

changes:
* decrease cur after deleting a delimiter with can_open = False
* add test
---
 marko/inline_parser.py | 1 +
 tests/test_spec.py     | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/marko/inline_parser.py b/marko/inline_parser.py
index e4d5bd9..e73d7c6 100644
--- a/marko/inline_parser.py
+++ b/marko/inline_parser.py
@@ -437,6 +437,7 @@ def process_emphasis(
                 underscore_bottom = bottom
             if not d_closer.can_open:
                 delimiters.remove(d_closer)
+                cur = cur - 1 if cur > 0 else None
         cur = _next_closer(delimiters, cur)
     lower = stack_bottom + 1 if stack_bottom is not None else 0
     del delimiters[lower:]
diff --git a/tests/test_spec.py b/tests/test_spec.py
index 2e72f56..22749fa 100644
--- a/tests/test_spec.py
+++ b/tests/test_spec.py
@@ -90,6 +90,11 @@ def gfm() -> Markdown:
         "![foo\nbar\nbaz](/image.png)",
         '<p><img src="/image.png" alt="foo\nbar\nbaz" /></p>',
     ),
+    (
+        "emphasis_underscore_in_strong",
+        "**a_{b}**",
+        "<p><strong>a_{b}</strong></p>",
+    )
 ]