From 7791b323c0c1e1e7d257b55d32c8941b43c65661 Mon Sep 17 00:00:00 2001
From: Sanjay Santhanam <51058514+Sanjays2402@users.noreply.github.com>
Date: Tue, 14 Jul 2026 17:22:31 -0700
Subject: [PATCH] FIX: Correct included source line attribution

Included Markdown applied a one-based offset before token maps were converted
to one-based source lines, shifting every diagnostic down by one line.

Pass the zero-based start line to the nested renderer and cover plain,
start-line, and nested includes.

Tests: python -m pytest -q
Fixes #1165
---
 myst_parser/mocking.py                        |  2 +-
 .../fixtures/mock_include_errors.md           | 19 ++++++++++++++++++-
 .../test_renderers/test_include_directive.py  |  2 ++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/myst_parser/mocking.py b/myst_parser/mocking.py
index f809c6d7..75d4beba 100644
--- a/myst_parser/mocking.py
+++ b/myst_parser/mocking.py
@@ -515,7 +515,7 @@ def run(self) -> list[nodes.Element]:
                 )
             self.renderer.nested_render_text(
                 file_content,
-                startline + 1,
+                startline,
                 heading_offset=self.options.get("heading-offset", 0),
             )
         finally:
diff --git a/tests/test_renderers/fixtures/mock_include_errors.md b/tests/test_renderers/fixtures/mock_include_errors.md
index 6e443cb6..6474a1be 100644
--- a/tests/test_renderers/fixtures/mock_include_errors.md
+++ b/tests/test_renderers/fixtures/mock_include_errors.md
@@ -19,5 +19,22 @@ Error in include file:
 ```{include} bad.md
 ```
 .
-tmpdir/bad.md:2: (WARNING/2) Unknown interpreted text role "a". [myst.role_unknown]
+tmpdir/bad.md:1: (WARNING/2) Unknown interpreted text role "a". [myst.role_unknown]
+.
+
+Error in include file with start line:
+.
+```{include} bad_start.md
+:start-line: 1
+```
+.
+tmpdir/bad_start.md:2: (WARNING/2) Unknown interpreted text role "a". [myst.role_unknown]
+.
+
+Error in nested include file:
+.
+```{include} outer.md
+```
+.
+tmpdir/bad.md:1: (WARNING/2) Unknown interpreted text role "a". [myst.role_unknown]
 .
diff --git a/tests/test_renderers/test_include_directive.py b/tests/test_renderers/test_include_directive.py
index 9f03d633..5aee3206 100644
--- a/tests/test_renderers/test_include_directive.py
+++ b/tests/test_renderers/test_include_directive.py
@@ -41,6 +41,8 @@ def test_errors(file_params, tmp_path, monkeypatch):
     monkeypatch.chdir(tmp_path)
 
     tmp_path.joinpath("bad.md").write_text("{a}`b`")
+    tmp_path.joinpath("bad_start.md").write_text("skip\n{a}`b`")
+    tmp_path.joinpath("outer.md").write_text("```{include} bad.md\n```")
 
     report_stream = StringIO()
     publish_doctree(