[wp-trac] [WordPress Trac] #49927: Editor: Introduce block context

[WordPress Trac]

#49927: Editor: Introduce block context
-------------------------+-----------------------------
 Reporter:  aduth        |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  Awaiting Review
Component:  Editor       |    Version:
 Severity:  normal       |   Keywords:
  Focuses:               |
-------------------------+-----------------------------
 Related: https://github.com/WordPress/gutenberg/pull/21467
 Related (blocked by): #49926

 The Gutenberg project is currently exploring the introduction of a new
 [https://github.com/WordPress/gutenberg/issues/19685 block context
 feature]. The purpose of this feature is to be able to establish values in
 a block hierarchy which can be consumed by blocks anywhere lower in the
 same hierarchy. These values can be established either by the framework,
 or by other blocks which provide these values.

 See documentation:
 https://github.com/WordPress/gutenberg/blob/29c6a1b/docs/designers-
 developers/developers/block-api/block-context.md

 This is planned to be used for:

 - Site blocks, to derive values from site settings
 - Post template blocks, to derive values from the "current" post
 - Navigation block, to derive values from the "current" menu

 Many of these use-cases are related to the current full-site editing
 efforts, currently slated for WordPress 5.5:
 https://make.wordpress.org/updates/2020/03/06/update-progress-on-goals/

 Prior art: Just as many of the full-site editing post blocks are intended
 to map to [https://developer.wordpress.org/themes/references/list-of-
 template-tags/#post-tags corresponding theme post tags], the role of block
 context can serve the role of
 [https://developer.wordpress.org/themes/basics/the-loop/ The Loop] in
 preparing the post for blocks within to consume from.

 Proposed tasks:

 - For making context available to blocks for `render_callback`, this
 relies on the proposal at #49926. There are earlier iterations of
 [https://github.com/WordPress/gutenberg/pull/21467 Gutenberg#21467] which
 assigned this context as a global variable and expected blocks to consume
 from the global, similar to the `$post` global. The changes introducing
 `WP_Block` sought to avoid these globals, but it is an alternative option
 if #49926 is not viable.
 - Introduce block context mechanism based on registered block settings for
 providing and consuming context. See implementation from
 [https://github.com/WordPress/gutenberg/pull/21467 Gutenberg#21467] for
 initial reference.
 -
 [https://developer.wordpress.org/reference/functions/get_block_editor_server_block_settings/
 `get_block_editor_server_block_settings`] should be updated to pick the
 new `providesContext` and `context` keys from the registered block's
 settings, in order to share these values between the server and client.
    - Optionally, the `$keys_to_pick` array within this implementation
 could be considered to be made filterable. It's not explicitly needed for
 core introduction, but is a challenge for external extensibility, like in
 the case of [https://github.com/WordPress/gutenberg/pull/21467
 Gutenberg#21467].

 Feedback welcome: While the above can be considered a proposal of tasks,
 this is all very much subject to change.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/49927>
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