Build on top of swift-markdown?

[kevinrenskers]

Apple now has https://github.com/swiftlang/swift-markdown, its own markdown parser, also based on https://github.com/swiftlang/swift-cmark.git (just like Parsley). It offers easy modification of the AST, something that Parsley does not offer, but is missing features that Parsley offers.

Parsley does the code block titles, handles frontmatter, and splits the first title from the body.
Swift Markdown does none of that, but has the AST modification.

I kinda wonder if Parsley should make be based on top of Swift Markdown 🤔 It could add the unique features that Swift Markdown is missing, getting the AST stuff for free.

We could keep the public API the same, with the same markdown options and syntax extensions, but add the markup rewriter stuff.

The code block title feature could become a MarkupRewriter that transforms the AST, which is cleaner than the current regex pre/post-processing approach.

[kevinrenskers]

Well, sadly swift-markdown's lack of configurability is a real problem:

• Extensions: Only 3 hardcoded (table, strikethrough, tasklist). No autolink, no tagfilter, and no API to choose which ones are active. Parsley's SyntaxExtension parameter becomes meaningless.
• Rendering options: No hardBreaks, no safe/unsafe mode. These are core Parsley features, not edge cases.
• Workarounds: Every missing feature would need a custom MarkupRewriter or post-processing hack, which is ironic given the whole point is getting cleaner architecture.

The value proposition of the migration was "same features + AST modification." But if you have to reimplement half of cmark-gfm's feature set yourself, you're trading well-tested C code for fragile Swift workarounds.

Contributing upstream to swift-markdown (making extensions configurable, adding rendering options) would be the right long-term play, but that's a separate project with its own timeline and review process. And until those PRs land, Parsley can't depend on it.

For now, Parsley on swift-cmark is the pragmatic choice — it works, it's tested, and the regex code fence title handling is a small price to pay compared to the alternative.

[kevinrenskers]

swift-markdown's HTMLFormatter output is not production ready yet. I've compared Parsley's output (which is made with cmark_render_html) with swift-markdown's output (using its HTMLFormatter) and the results are rough.

Issue	cmark_render_html	HTMLFormatter
No HTML escaping in code	&lt;div&gt;	<div> (raw HTML in code blocks!)
No autolinks	<a href="...">www.example.com</a>	www.example.com (plain text)
No safe mode	<!-- raw HTML omitted -->	Passes HTML through
No hard breaks	<br />\n	Always \n
Smart quotes always on	&quot;test&quot; by default	\u{201C}test\u{201D} always
List items wrapped in <p>	<li>item</li>	<li><p>item</p>\n</li> (loose lists)
Image alt text dropped	alt="alt text"	No alt attribute
Link title dropped	title="Title"	No title attribute