wp_get_global_styles: return values instead of CSS Custom Properties

[oandregal]

Related #49693 #45171

What problem does this address?

The wp_get_global_styles function returns the content in the theme.json.

For example, for a content such as:

"core/post-terms": {
    "typography": { "fontSize": "var(--wp--preset--font-size--small)" }
}

The expected result is:

(
    [typography] => Array( [fontSize] => var(--wp--preset--font-size--small) )
)

Some environments don't have support for CSS Custom Properties. For example, mobile or email templates. They have to parse the content to understand it and convert it to a value they can use.

What is your proposed solution?

There are two alternatives we could explore to help them use theme.json provided values:

• Add some new parameter to wp_get_global_styles that tells the function to resolve the CSS Custom Properties to the value they reference.
• Create a new function, for example wp_get_global_styles_values, that does the same.

[samnajian]

@oandregal I'd rather go with your second proposal since:

1. The use case is pretty limited for now, so it's better to not adjust the main, more multi-purpose function to do even more
2. wp_get_global_styles is already receiving 2 parameters in the form of arrays, which in the absence of proper typing on the language level are confusing enough, so refraining from adding a new parameter to the same rather complex input parameters would keep the complexity the same and not add to it.

So basically by introducing a new function, we can keep the complexity to the underlying classes and not push it to the user side.

[oandregal]

Relevant thread for this conversation, so we can see everything together https://github.com/WordPress/gutenberg/pull/50484/files#r1192502874

[oandregal]

This has been fixed by #50484