bump pymdown-extensions to fix NoneType bug (#9319)

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Closes #9316 

mo.doc(mo.hstack) (and any other @mddoc-decorated callable) crashed with
AttributeError: 'NoneType' object has no attribute 'replace' when
resolved against pygments>=2.20 + pymdown-extensions<10.21.2.

The root cause is upstream: pymdown-extensions <10.21.2 passes
filename=None to pygments' HtmlFormatter, and pygments 2.20 stopped
tolerating that. Fix released in [pymdown-extensions
10.21.2](http://facelessuser.github.io/pymdown-extensions/about/changelog/),
so we bump our lower bound.

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Author: Light2Dark

pyproject.toml

@@ -18,7 +18,7 @@ dependencies = [
     "markdown>=3.6,<4",
     # add features to markdown
     # Pinned to specific version for introduction of codeblock handling.
-    "pymdown-extensions>=10.15,<11",
+    "pymdown-extensions>=10.21.2,<11",
     # syntax highlighting of code in markdown
     "pygments>=2.19,<3",
     # for reading, writing configs
@@ -268,7 +268,7 @@ docs = [
     "pillow>=10.2.0,!=11.3.0",  # for social cards, 11.3.0 doesn't have manylinux wheels
     "cairosvg>=2.7.1",  # for social cards
     "mdx-include>=1.4.2",
-    "pymdown-extensions>=10.7",
+    "pymdown-extensions>=10.21.2",
     "lzstring>=1.0.4",
     "beautifulsoup4>=4.12.0",
     "markdownify>=0.13.0",

tests/_output/test_doc.py

@@ -0,0 +1,48 @@
+# Copyright 2026 Marimo. All rights reserved.
+"""Tests for `marimo._output.doc.doc` / `mo.doc`."""
+
+from __future__ import annotations
+
+import marimo as mo
+from marimo._output.doc import doc
+from marimo._output.hypertext import Html
+
+
+def test_doc_on_mddoc_decorated_function_does_not_raise() -> None:
+    """Regression test for https://github.com/marimo-team/marimo/issues/9316.
+
+    `mo.doc` renders `_rich_help_` output (which contains a ```python fenced
+    code block with the object's signature) through pymdown-extensions +
+    pygments. pymdown-extensions <10.21.2 passed `filename=None` to pygments'
+    `HtmlFormatter`, and pygments >=2.20 crashed with
+    `AttributeError: 'NoneType' object has no attribute 'replace'`.
+
+    This test exercises the full pipeline end-to-end on each `@mddoc`-decorated
+    object used by the Layout tutorial so a regression in the pinned dependency
+    range is caught immediately.
+    """
+    for obj in (mo.hstack, mo.vstack, mo.accordion, mo.callout, mo.tree):
+        result = doc(obj)
+        assert isinstance(result, Html), (
+            f"doc({obj.__name__}) returned {result!r}"
+        )
+        # The highlighted signature block should be present in the output.
+        assert "codehilite" in result.text
+        assert obj.__name__ in result.text
+
+
+def test_doc_on_mddoc_decorated_method_does_not_raise() -> None:
+    for method in (mo.Html.center, mo.Html.right, mo.Html.left):
+        result = doc(method)
+        assert isinstance(result, Html)
+        assert "codehilite" in result.text
+
+
+def test_doc_on_object_without_rich_help_returns_none() -> None:
+    """When the target object doesn't implement `_rich_help_`, `doc` should
+    fall back to `help(obj)` and return `None`."""
+
+    class Plain:
+        """A plain class without `_rich_help_`."""
+
+    assert doc(Plain) is None

tests/snapshots/dependencies.txt

@@ -9,7 +9,7 @@ narwhals>=2.0.0
 packaging
 psutil>=5.0
 pygments>=2.19,<3
-pymdown-extensions>=10.15,<11
+pymdown-extensions>=10.21.2,<11
 pyyaml>=6.0.1
 pyzmq>=27.1.0; python_version < '3.15'
 starlette>=0.37.2