fix: handle TypeError when source is None in Sphinx 8.2

Fixes sphinx-contrib#234

When docutils.utils.get_source_line() returns None for the source
parameter, the code was attempting to call osutil.relpath(None),
which caused a TypeError in Sphinx 8.2.3.

This can occur with programmatically generated nodes or certain
document structures that don't have proper source attribution.

Changes:
- Added null check before calling osutil.relpath() in builder.py
- Use '<unknown>' placeholder when source is None
- Added test case that reproduces the issue and verifies the fix

Chat log: https://gist.github.com/dhellmann/27d64eb733af50a2c1e460cc40164a11

Co-authored-by: Claude Sonnet 4.5 <[email protected]>
Signed-off-by: Doug Hellmann <[email protected]>

Author: dhellmann

sphinxcontrib/spelling/builder.py

@@ -228,7 +228,12 @@ def filter(n):
             # the full path, so convert all to relative path
             # for consistency.
             source, node_lineno = docutils.utils.get_source_line(node)
-            source = osutil.relpath(source)
+            if source is not None:
+                source = osutil.relpath(source)
+            else:
+                # Some nodes (e.g., programmatically generated) may not have
+                # source information. Use a placeholder.
+                source = "<unknown>"
 
             # Check the text of the node.
             misspellings = self.checker.check(node.astext())

tests/test_builder.py

@@ -677,3 +677,77 @@ def test_only_directive(sphinx_project):
     )
     assert "(whaat)" in output_text
     assert "(teh)" not in output_text
+
+
+def test_nodes_with_none_source(sphinx_project):
+    # Reproduces https://github.com/sphinx-contrib/spelling/issues/234
+    # Tests handling of nodes where get_source_line returns None for source
+    srcdir, outdir = sphinx_project
+
+    # Create an extension that patches docutils.utils.get_source_line to return None
+    # This directly simulates the bug condition
+    add_file(
+        srcdir,
+        "mock_none_source.py",
+        """
+import docutils.utils
+
+
+# Store the original function
+_original_get_source_line = docutils.utils.get_source_line
+
+
+def patched_get_source_line(node):
+    '''Return None for source to simulate issue #234'''
+    # Call original to get line number
+    source, lineno = _original_get_source_line(node)
+    # But return None for source to trigger the bug
+    return (None, lineno)
+
+
+def setup(app):
+    # Patch the function when building
+    def on_build_finished(app, exception):
+        # Restore original after build
+        docutils.utils.get_source_line = _original_get_source_line
+
+    # Patch before doctree-read
+    def on_doctree_read(app, doctree):
+        docutils.utils.get_source_line = patched_get_source_line
+
+    app.connect('doctree-read', on_doctree_read, priority=1)
+    app.connect('build-finished', on_build_finished)
+
+    return {'version': '0.1'}
+    """,
+    )
+
+    add_file(
+        srcdir,
+        "conf.py",
+        f"""
+import sys
+sys.path.insert(0, r'{srcdir}')
+extensions = ['sphinxcontrib.spelling', 'mock_none_source']
+    """,
+    )
+
+    add_file(
+        srcdir,
+        "contents.rst",
+        """
+    Test Document
+    =============
+
+    This text has a mispeling that should be caught.
+    """,
+    )
+
+    # Without the fix, this will crash with:
+    # TypeError: expected str, bytes or os.PathLike object, not NoneType
+    # With the fix, it should handle None gracefully and produce output
+    stdout, stderr, output_text = get_sphinx_output(srcdir, outdir, "contents")
+
+    # The spelling check should still work and find the misspelling
+    assert output_text is not None
+    assert "(mispeling)" in output_text