Fixing an abstract syntax tree bug in Gatsby Remark oEmbed

On yesterday's unauthorized and rum-fueled treasure hunt in the sharky waters around the Gatsby islands, we fixed Issue #102: <div> cannot appear as a descendent of <p>.

YouTube Screengrab

To understand why this was happening, let us take a step back and look at how markdown can be represented as an Abstract Syntax Tree.

Markdown Abstract Syntax Tree (mdast)

The following markdown:

Intro text, [A link](!

[Another Link](

- [A third link](
- Some text

as a Markdown Abstract Syntax Tree (mdast):

Markdown Abstract Syntax Tree

Each box is called a node, a tree always springs out from a root node, and the nodes without any children are called leaves.

And yes, it is an upside-down tree as Ola pointed out 🤪

Our code

Gatsby Transformer Remark takes the markdown files, transforms the markdown into mdast, and passes it onto our plugin. We then "walk" the tree looking for standalone links.

Markdown Abstract Syntax Tree

Then we swap out the link node for an HTML node if it is indeed an oEmbed link:

const tranformsLinkNodeToOembedNode = ({ node }, oembedResult) => {
  node.type = "html";
  node.value = oembedResult.html;
  delete node.children;

Giving us a slightly modified tree:

Markdown Abstract Syntax Tree

Can you spot the mistake?


Our problem

The HTML node is a child of a paragraph node. Depending on the oEmbed HTML this might result in an invalid HTML structure when the mdast converts into HTML.

The solution

Pass along the parent paragraph node as the node to be exchanged for an html node instead!

Markdown Abstract Syntax Tree

All the best,
Queen Raae

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