gh-122163: Add notes for JSON serialization errors

[serhiy-storchaka]

This allows to identify the source of the error.

• Issue: Add details for JSON serialization errors #122163

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📚 Documentation preview 📚: https://cpython-previews--122165.org.readthedocs.build/

[iritkatriel]

LGTM

[nineteendo]

Serhiy, how can I do this in a third party library? _PyErr_FormatNote() is not part of the public API.
Or should I use a different approach? Like creating a JSON path. "/foos/1/bar" and adding it to the error message.

[serhiy-storchaka]

You can do this by implementing your own _PyErr_FormatNote() or like. Create a string object and call the add_note() method of the exception.