[wp-trac] [WordPress Trac] #59776: Block Hooks: Allow traversal callbacks to modify parent block

[WordPress Trac]

#59776: Block Hooks: Allow traversal callbacks to modify parent block
------------------------------+------------------------------
 Reporter:  Bernhard Reiter   |       Owner:  Bernhard Reiter
     Type:  defect (bug)      |      Status:  closed
 Priority:  normal            |   Milestone:  6.4
Component:  Editor            |     Version:  trunk
 Severity:  normal            |  Resolution:  fixed
 Keywords:  has-patch commit  |     Focuses:
------------------------------+------------------------------
Changes (by Bernhard Reiter):

 * owner:  (none) => Bernhard Reiter
 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"57038" 57038]:
 {{{
 #!CommitTicketReference repository="" revision="57038"
 Block Hooks: Allow traversal callbacks to modify parent block.

 The callbacks returned by `make_before_block_visitor` and
 `make_after_block_visitor`, respectively, (which are passed as arguments
 to `traverse_and_serialize_block(s)`) currently accept three arguments,
 all of which are block arrays (i.e. with properties `blockName`, `attrs`,
 etc.):
 - A ''reference'' to the block they're currently visiting, `&$block`;
 - the block's `$parent_block`; and
 - the `$prev`ious block (for `make_before_block_visitor`), or the `$next`
 block (for `make_after_block_visitor`), respectively.

 Those arguments are passed to the "block visitor" callbacks by
 `traverse_and_serialize_block(s)` during traversal. The block that the
 callback is currently visiting is passed ''by reference'' to allow
 modifying it, which is e.g. used to inject the `theme` attribute into
 Template Part blocks.

 One major limitation of Block Hooks is that they currently only work with
 templates, parts, and patterns that ''don't have any user modifications''
 (i.e. that come straight from the corresponding theme files, rather than
 from the database). For WordPress 6.5, it is planned to change that to
 make Block Hooks work for templates, parts, and patterns that ''do'' have
 user modifications: #59646.

 This will be implemented by storing an attribute on the "anchor" block.
 While working on that feature, it was found that the aforementioned
 callbacks will need to modify not only the currently visited `$block`, but
 also the `$parent_block` -- i.e. that the latter argument needs to be
 passed by reference as well. This is consistent with the requirement of
 adding an attribute to an anchor block, as it's not only the currently
 visited block that can serve as an anchor block (in the case of `before`
 or `after` sibling insertion), but also its parent (for `first_child` and
 `last_child` insertion).

 If the `$parent_block` argument were to be changed to become a reference
 in a later WordPress version, this could be considered a backwards-
 compatibility breaking change. For this reason, this change is instead
 proposed for 6.4 already, which is the cycle during which the relevant
 functions were first introduced. This should have no impact on existing
 code, since nothing currently relies on `$parent_block` remaining
 unmodified by the respective callback, nor is anything currently modifying
 that argument.

 Props hellofromTonya.
 Fixes #59776.
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/59776#comment:7>
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