Block Hooks: Allow insertion as first or last child of Template Part block

[Bernhard Reiter]

In ​GB#57754, a mechanism was introduced to allow insertion of hooked blocks into the Navigation block, in particular as its first_child or last_child, thus fixing #59743. The latter was achieved by storing the ignoredHookedBlocks array in the corresponding wp_navigation post's post meta (instead of a metadata attribute on the anchor block).

This technique could be applied to other blocks that fetch their inner blocks from a separate DB record (rather than having them stored inline); these are sometimes referred to as "controlled inner blocks".

There might not be a large number of container blocks with controlled inner blocks into which we'd want to inject hooked blocks; however, there's at least one obvious example: The Template Part block. It's currently not possible to inject a hooked block as its first or last child.

Note however that the code that inserts hooked blocks into the Navigation block's wp_navigation post objects currently lives in Gutenberg. Consequently, it's advisable to absorb that code into Core first (i.e. to fix #60759) before tackling this issue.

Trac ticket: https://core.trac.wordpress.org/ticket/60854

Is it possible to get away with even fewer changes (to block-template-utils.php, specifically) if we hook update_ignored_hooked_blocks_postmeta into rest_pre_insert_wp_template_part (like ​we already do for wp_navigation posts)?

As it stands using that filter in the templates controller only gives us the following information; post_name, ID, post_status and post_content so we don't know if its a wp_template or wp_template_part since we don't have the post type there.

Is that really a problem though? Can't we implicitly assume wp_template_part, since we'll be only hooking to rest_pre_insert_wp_template_part (but not to rest_pre_insert_wp_template)? 🤔

Another thing I realized is that on a higher level, update_ignored_hooked_blocks_postmeta only updates the ignoredHookedBlocks metadata (as the function name states 😅 ); it doesn’t actually take care of block insertion (neither in the editor, nor on the frontend). So those parts would still be missing.

For the editor (i.e. the REST API), we might be able to use insert_hooked_blocks_into_rest_response (once again like we do for wp_navigation). The frontend is a bit trickier though.

So those parts would still be missing

Unless I'm misunderstanding what you're saying here. Those pieces are covered by the updates I made to _build_block_template... functions since these functions are used both when building the template for the REST response _and_ the frontend. Are you suggesting I find a different way to insert the hooked blocks?

So those parts would still be missing

Unless I'm misunderstanding what you're saying here. Those pieces are covered by the updates I made to _build_block_template... functions since these functions are used both when building the template for the REST response _and_ the frontend. Are you suggesting I find a different way to insert the hooked blocks?

No, that's fine! I guess I was hoping to unify first/last child insertion into wp_navigation and wp_template_part posts even more but got my wires crossed 😅

I've just committed ​https://github.com/WordPress/wordpress-develop/pull/6885 to Core, so we can rebase this now. (We'll probably need to change the remaining assertions that are using get_post_meta() to get _wp_ignored_hooked_blocks to $post->meta_input['_wp_ignored_hooked_blocks'], like you did in #6885.)

[Bernhard Reiter]

In 58614:

Block Hooks: Allow child insertion into Template Part block.

The Block Hooks mechanism was previously extended to allow insertion of a block as a Navigation block's first or last child. This was implemented by storing the ignoredHookedBlocks array in the corresponding wp_navigation post's post meta (instead of a metadata attribute on the anchor block).

This changeset extends that mechanism to Template Part blocks, by storing said metadata in the corresponding wp_template_part post's post meta, thus allowing extenders to use Block Hooks to insert a block as a Template Part block's first or last child, respectively.

Props tomjcafferkey, bernhard-reiter.
Fixes #60854.

Committed to Core in https://core.trac.wordpress.org/changeset/58614.

@ockham Left two nit-pick feedback.

[Bernhard Reiter]

In 58615:

Block Hooks: Fix a number of multi-line comment openers.

Add the missing second asterisk to a number of multi-line comment openers, and remove a superfluous second asterisk from two others.

Follow-up to [58614].
Props mukesh27.
See #60854.

@ockham Left two nit-pick feedback.

Fixed in https://core.trac.wordpress.org/changeset/58615. Thank you!

[Bernhard Reiter]

Dev Note draft available ​here.