HTML files should be able to reference any local assets

[iainmerrick]

Summary

HTML files should be able to reference any local assets, in the same way as Markdown files.

Background & Motivation

Currently, HTML files can only reference assets in the public/ folder. This means if you have an existing HTML file referencing local assets, it can't simply be dropped into the pages/ folder as-is.

This is unlike Markdown, which can reference local assets and have them automatically transformed into content-hashed URLs. HTML should behave the same way as MarkDown.

There is no existing behaviour for local asset references that people might be relying on. In cases where users do want an exact asset URL with no bundling, they can use the existing mechanism of putting their files in public/.

This would be consistent with Astro's principles of building on web standards. Why Astro says "You can build a 'hello world' example website in Astro with just HTML and CSS". Let's expand that to "HTML, CSS and images"!

Goals

• HTML files with local assets should work as-is, in the same way as Markdown files.
• This will remove an unnecessary barrier to importing existing sites into Astro.

Example

Given a tag like this referencing a local image:

<img src="_foo.png">

I would expect the output to look like:

<img src="/_astro/_foo.123456.png">

Minimal example: https://stackblitz.com/edit/github-uepn1b

Related issues

• I originally filed this as an issue (Asset links are not bundled in .html files astro#10928) and was recommended to write it up as a proposal instead.
• There's a separate issue relating to HTML syntax in Markdown files: Images are not collected in Markdown files when using HTML syntax #873. I propose that this should be fixed consistently in both Markdown and HTML files.