Adding Subsets for Custom Packager

[ayuhito]

Description

The current custom packager only defaults to subset latin since it has no information on what subsets a given font may support. Therefore, we can't give it proper unicode-range values either. We should have a preprocessor that determines what subsets the font supports and split it accordingly matching how Google does it.

[tmikaeld]

Is this why ext fonts doesn't render properly at all?

For example, courier prime latin looks like this:

But the latin ext woff2 looks like this:

I noticed when testing on https://fontsource.org/fonts/courier-prime that it doesn't load the ext font att all when choosing it from the dropdown, it's still showing latin.

Update: Seems all ext fonts are broken

[ayuhito]

@tmikaeld, that is intentional. latin-ext does not support any characters latin does. They are exclusionary to each other. For example, latin-ext only includes support for diacritics etc.

Usually our CSS files include both and the unicode-range selector automatically determines what subsets to download depending on the characters on the page.

I suppose our subsets documentation could be improved to make that distinction clearer.

[tmikaeld]

Right, so both latin and latin-ext should be loaded.

Does this apply to any other subsets?

[ayuhito]

Does this apply to any other subsets?

It applies to all other subsets. They only support their specific range of characters and you need to combine them with unicode-range.

The only case this does not apply is non-Google fonts where our custom packager for that does not support subsetting and therefore every subset is usually included in one file.

[tmikaeld]

I'll move to a discussion instead of polluting this issue.