[Bug]: preload: false does not work for custom font

[ChristopherJohnson25]

Demo URL

No response

What happened?

setting preload: false does not work for custom font

Reproduction steps

1. add preload: false to options
2. observe that fonts are still preloaded

Relevant log output

No response

What browsers are you seeing the problem on?

Chrome

What is your operating system?

MacOS

[BenBE]

While reading through the source code, I noticed, that generating tags is unconditional for all generated link tags. Thus whenever a bundled asset matches the filename pattern for a font file, there will be a tag for it. Kinda unintuitively the settings under options.custom.prefetch and options.custom.preload are applied for all fonts, including Google Fonts, Font Source, etc.

Unfortunately, there's a bit of code duplication for the actual link tag generation, which makes the fix for this a bit spread all around the code base.

The outline for this is basically:

• Find all places where getHeadLinkTags is called.
• Look at the for (const file of files) loop directly below
• The tags.push() there needs to be conditional on options.custom.prefetch || options.custom.preload

While at it and looking in the context of #10, after that for loop is also the ideal place to introduce a new callback options.custom.linkFilter hook, that in the simplest case just receives the tags array and could then do:

• return true -> return tags unaltered
• return false -> return no tags
• return a modified tag array -> forward the modified choice of headers to generate