Updated July 10, 2021
So um, they don't actually work yet, because of a theming issue... I'll get to it later.
exports.onCreateNode = ({ node, getNode, actions }) => {
const { createNodeField } = actions;
if (node.internal.type === `Mdx`) {
const value = createFilePath({ node, getNode });
console.log(value);
createNodeField({
name: `slug`,
node,
value,
});
}
};