feat(markdown): add support for TOML frontmatter in Markdown files.

[colinbate]

Changes

• Changed the frontmatter parsing in @astrojs/markdown-remark to accept TOML format
• Uses +++ as the delimiters
• Doesn't require configuration
  • If the TOML delimiters are used it will parse as TOML
  • Otherwise defaults to YAML

Testing

Updated the frontmatter.test.js file, adding TOML equivalent tests alongside the existing YAML tests. Worth noting that the TOML test run notably faster, owing to the faster parsing

Docs

This is certainly something that should be documented. It allows you to use TOML based frontmatter, which is particularly useful if migrating from Hugo or another system that preferred TOML and you don't want to convert potentially thousands of files.

Works for content collections, or with standalone markdown files.

/cc @withastro/maintainers-docs for feedback!

[ematipico]

Why would we allow TOML frontmatter in .mdx files but not in .md files? It seems a missed opportunity

[colinbate]

@ematipico Apologies, I didn't mean to imply this was only for MDX files. It works for both.