Add class name for block variations

[Bernhard Reiter]

In order to allow block authors to add custom styling for individual block variations, it would be convenient to have a class name automatically added for the variation.

There's some ​precedent in the Social Icon block, which e.g. for its WordPress variation adds the wp-social-link-wordpress class name (in addition to wp-social-link).

For a given block my/block with a variation myvariation that's registered on the server side (via ​`variation_callback` or ​`get_block_type_variations`), add a class wp-block-my-block-mynavigation to the block wrapper.

### Design choiced

This PR introduces a new function called get_active_block_variation(), which is modelled after its client-side counterpart, ​`getActiveBlockVariation()`. The signatures are _almost_ identical, the major difference being that the client-side version accepts a block type _name_, whereas the server side one expects a WP_Block_Type object.

Inference. Note that while get_active_block_variation respects the isActive field to determine the variation of a block given its attributes, it also has a fallback mechanism, which is to compare the variation's set of defining attributes to the block's.

I believe that this is a reasonable technique to determine a block variation, especially in the absence of an isActive field (which on the server side is furthermore limited to an array of attributes that need to be considered in determining a variation, as opposed to the client side, where arbitrary callbacks are allowed for isActive).

If we agree with this fallback mechanism, I'm inclined to add it to the client side's getActiveBlockVariation as well.

### TODO

• [ ] Test coverage
• [ ] PHPDoc
• [ ] scope arguments

### Testing Instructions

Test with a Block Theme (such as TT4) that uses Template Part block (and ideally also Navigation Link blocks), as those are among the few blocks with server-side registered variations. Inspect the page source and verify that the aforementioned blocks have indeed a variation-specific classname added, e.g. wp-block-template-part-area_footer or wp-block-navigation-link-page.

### Screenshots

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Trac ticket: https://core.trac.wordpress.org/ticket/61265

I'm assuming we're going to need to open a GB counterpart to deal with the same logic for adding variation class names in the editor too?

I'm assuming we're going to need to open a GB counterpart to deal with the same logic for adding variation class names in the editor too?

Oh, good point! I was originally just focused on dynamic blocks, but you're right, we'll probably need something somewhere around addGeneratedClassName and/or getBlockDefaultClassName.

I'm assuming we're going to need to open a GB counterpart to deal with the same logic for adding variation class names in the editor too?

Oh, good point! I was originally just focused on dynamic blocks, but you're right, we'll probably need something somewhere around addGeneratedClassName and/or getBlockDefaultClassName.

@tjcafferkey Mind giving that a stab? 😄

Mind giving that a stab? 😄

I'd love to!

[oglekler]

Hi @bernhard-reiter It looks quite well-defined, but we have just a few days before Beta 1, it can possibly go into 6.6 if we hurry up. Can you please provide testing instructions? Thank you!

[faisal03]

== Test Report

Please ignore, it was meant for https://core.trac.wordpress.org/ticket/60236

[gziolo]

Moving to WordPress 6.7.