theme.json v2: track changes

[oandregal]

Part of #20331

This issue is to track the changes we need to introduce in WordPress 5.9, which we should match to a new schema for theme.json.

• Update version to 2.
• Consolidate the names that already landed and add migration from v1 to v2:
  • Rename spacing.customMargin to spacing.margin.
  • Rename spacing.customPadding to spacing.padding.
  • Rename typography.customLineHeight to typography.lineHeight.
• Add the new properties to VALID_SETTINGS and VALID_STYLES.
• Theme.json: Remove custom prefixes from properties that did not land in 5.8 #34485

[oandregal]

In origin, we used the custom* prefix for things that had both a preset and custom colors added by the user. For example, color.customGradient means the users can't use the custom colors in gradients, they are limited to preset gradients. However, color.link means the users can't set link color.

We should remove the custom* prefix those properties that don't need it: spacing.margin, spacing.padding, typography.lineHeight.

[oandregal]

cc @mtias @youknowriad @mcsf @jorgefilipecosta @gziolo @aaronrobertshaw @ramonjd

We can implement the migration from v1 to v2 for the properties above, as we did in the plugin when we introduced v1 (see), so in theme.json you'd use the name without the custom prefix.

I wonder how this affects the "internal" names: ideally, the names of the properties in the __experimentalFeatures passed to the client can be also updated as well as the store. I understand this may require 3rd parties that hook into the block settings filter to update their filters, if they modify these values. Is this a reasonable request? I think it is, because a theme.json v2 could introduce shape changes anyway.

[mtias]

We should perhaps leave the renaming for when we stabilize and remove the __experimental.

[uniquesolution]

How about having multiple conditional theme.json files, so that one site can have multiple theme global styls for different pages conditionally? For example as we select page template is in page editor, how about having an option to also choose a different theme.json file ?

[mtias]

Multiple json files is indeed on the roadmap and conceptualized in the initial scope. The idea is it can be composed in a similar way to the theme hierarchy — so it can match a set of templates, or an individual page, etc. The idea is that template parts could also be theme.json providers, meaning you could overwrite or specify settings for ay template part in complex scenarios. Think a case where a sidebar might require a different set of color presets than the rest of the site.

Swapping theme.json files altogether will also be a good affordance for themes offering different schemes, etc. A dark theme could also be conceptualized under that model easily.

[uniquesolution]

Is this coming in Wordpress 5.9 ? Where we can see progress in this topic ? I would like see this particular topic progress and want to participate in suggestion if I find useful.

[oandregal]

PRs to remove the custom prefix from existing v1 settings at #36154 and #36155

[oandregal]

All tasks here have landed so I'm closing this. For reference, I'm porting the changes to WordPress core at WordPress/wordpress-develop#1808