[Markdoc] Modify frontmatter inside document's transform function

[viscid steeple]

According to the markdoc docs (https://markdoc.dev/docs/nodes#built-in-nodes), the node type document should store the frontmatter in an attribute called frontmatter (as shown in the sandbox https://markdoc.dev/sandbox?mode=ast)

However, I can't access it from the transform function:

nodes: {
    document: {
        render: null,
        attributes: {
            frontmatter: { type: String },
        },
        transform(node: Node, config: Config): RenderableTreeNode | RenderableTreeNode[] | null {
            const children = node.transformChildren(config);
            const attributes = node.transformAttributes(config);

            console.log(node.attributes) // Prints empty object
            console.log(attributes) // Prints empty object
            console.log(config.variables?.entry.data) // Prints the frontmatter

            return children
        }
    }
}

I have also tried to change the type of the attribute to Object, but no change. And if I add required: true I get a missing attribute error (failed to validate: attribute-missing-required).

I'm aware that I don't need to do that in the transform function (i.e. I can do it by parsing with Markdoc.parse(entry.body) the same way one would extract the headings)

Is it possible to modify the frontmatter in the transform function in a similar way one would use a remark plugin to do so?

[abstract lance]

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[candid briar]

He luliic2! Since Markdoc is built on content collections, we avoid passing a "raw" frontmatter object (aka unparsed by your content schema) to Markdoc. We hadn't realized frontmatter was a property supplied by document in Markdoc though, since it appears to be an optional property elsewhere in the documentation

Is there a reason you'd prefer to modify frontmatter from your Markdoc config, instead of using a Zod transform from your content config? (example here https://docs.astro.build/en/guides/content-collections/#defining-datatypes-with-zod)

[viscid steeple]

Hi!

It's less about modifying the frontmatter and more about adding to it, similar to remarkPluginFrontmatter (https://docs.astro.build/en/guides/content-collections/#modifying-frontmatter-with-remark)

For example, I use the document's transform method to wrap h2s and it's subsequent tags in <section>s. And while I'm already iterating over the AST I want to calculate the reading time, however I can't pass that information (apart from embedding it directly into the AST). I'm left forced to parse it again after Astro via Markdoc.parse, at which point I might as well embed the html directly instead of calling entry.render