gutenberg / lib / compat / wordpress-7.1 / class-gutenberg-view-config-data.php

class-gutenberg-view-config-data.php in Gutenberg 23.7.2, at lib/compat/wordpress-7.1/class-gutenberg-view-config-data.php

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1	<?php
2	/**
3	* Gutenberg_View_Config_Data class
4	*
5	* @package gutenberg
6	*/
7
8	/**
9	* Holds an entity's view configuration while it is being built.
10	*
11	* An instance of this class is what `get_entity_view_config_{$kind}_{$name}`
12	* filter callbacks receive: a callback changes the configuration by calling
13	* methods on the instance and returning it. The configuration has four
14	* top-level keys — `default_view`, `default_layouts`, `view_list`, and
15	* `form` — and there are three ways to contribute. They form a gradient of how
16	* deep the replacement reaches:
17	*
18	* - The `merge()` method merges partial changes (patches) into what is already
19	* there: `default_view`, `default_layouts`, and the `form` settings by key,
20	* and the `view_list` entries by view `slug` identity. This is what plugins
21	* should use: patches compose with core's configuration and with other
22	* plugins'.
23	* - `replace()` applies a patch the same way `merge()` does, with one
24	* difference: a list in the patch replaces the current list wholesale
25	* instead of merging into it by member identity. It shouldn't be the
26	* default choice — a callback that replaces a list stops inheriting core's
27	* future additions to it — but it's useful when a contributor needs to pin
28	* a list to an exact set of members.
29	* - `set()` goes one step further: it replaces each top-level key the patch
30	* names wholesale, dropping whatever that key held instead of merging into
31	* it. It's for a callback that owns a key outright and wants to pin it to an
32	* exact shape without the inherited default leaking through a key-by-key
33	* merge.
34	*
35	* All three touch only the top-level keys the patch names — an omitted key
36	* keeps whatever it had, and a top-level `null` value drops the key it names,
37	* which resets it to its default. They differ only in how deep the replacement
38	* reaches once a key is named: `merge()` and `replace()` merge the value in
39	* key by key (an associative array merges member by member, a nested `null`
40	* deletes just that leaf, a scalar replaces just that value), while `set()`
41	* swaps the whole value. A nested `null` deletes just the leaf it names in
42	* every case. A patch value whose shape does not match the current value —
43	* an associative array where a list lives, or the reverse — is rejected with
44	* a notice rather than merged, and an empty array under `merge()` is a
45	* no-op. Each patch also declares the configuration schema
46	* version it was written against (currently 1), so a future WordPress release
47	* that changes the configuration shape can migrate existing patches forward
48	* instead of breaking them.
49	*
50	* Where those three write values, `remove()` deletes them: it takes a spec of
51	* names — a list to delete entries at a level, or a nested map to reach deeper —
52	* and prunes just what it names, mirroring the configuration's shape all the way
53	* down to individual list members.
54	*
55	* @since 7.1.0
56	*/
57	class Gutenberg_View_Config_Data {
58
59	/**
60	* The latest supported configuration schema version.
61	*
62	* @since 7.1.0
63	* @var int
64	*/
65	const LATEST_VERSION = 1;
66
67	/**
68	* The documented top-level configuration keys.
69	*
70	* @since 7.1.0
71	* @var string[]
72	*/
73	const CONFIG_KEYS = array( 'default_view', 'default_layouts', 'view_list', 'form' );
74
75	/**
76	* The configuration being contributed to.
77	*
78	* @since 7.1.0
79	* @var array
80	*/
81	private $config;
82
83	/**
84	* The default configuration.
85	*
86	* @since 7.1.0
87	* @var array
88	*/
89	private $defaults;
90
91	/**
92	* Constructor.
93	*
94	* @since 7.1.0
95	*
96	* @param array $config The base configuration to contribute to.
97	*/
98	public function __construct( array $config ) {
99	$this->config = $config;
100	$this->defaults = $config;
101	}
102
103	/**
104	* Returns the current configuration array.
105	*
106	* Deliberately private: filter callbacks receive the container, not the
107	* materialized configuration, so they cannot read the built result and
108	* become coupled to a specific configuration shape or schema version. Only
109	* the class itself reconciles the container back into an array.
110	*
111	* @since 7.1.0
112	*
113	* @return array The configuration.
114	*/
115	private function get_data() {
116	return $this->config;
117	}
118
119	/**
120	* Applies the entity view configuration filter and returns the result.
121	*
122	* Exposes the container through the dynamic
123	* `get_entity_view_config_{$kind}_{$name}` filter so that core and third
124	* parties can provide the configuration for a specific entity, then
125	* reconciles the filtered container back into a plain configuration array,
126	* limited to the documented configuration keys.
127	*
128	* @since 7.1.0
129	*
130	* @param string $kind The entity kind (e.g. `postType`).
131	* @param string $name The entity name (e.g. `page`).
132	* @return array The filtered configuration, limited to the documented keys.
133	*/
134	public function apply_filters( $kind, $name ) {
135	/**
136	* Filters the view configuration for a given entity.
137	*
138	* The dynamic portions of the hook name, `$kind` and `$name`, refer to the
139	* entity kind (e.g. `postType`) and the entity name (e.g. `page`).
140	*
141	* Callbacks receive a Gutenberg_View_Config_Data object and change the
142	* configuration through its methods. Each write method takes the schema
143	* version the change was authored against as its second argument,
144	* and returns the object for chaining:
145	*
146	* - `merge( $patch, $version )` merges a partial change into the current
147	* configuration. It touches only the top-level keys the patch names, and
148	* merges each named value into the current one by shape: a scalar
149	* replaces, an associative array merges key by key, and a list merges by
150	* member identity (`id`, `slug`, or `field`). A `null` value drops the
151	* key it names, resetting it to its default.
152	* - `replace( $patch, $version )` applies a patch exactly like `merge()`,
153	* but swaps any list it names wholesale instead of merging that list by
154	* member identity.
155	* - `set( $patch, $version )` also touches only the keys the patch names,
156	* but swaps each named value in wholesale, dropping whatever the key held
157	* before — for a callback that owns those keys outright.
158	* - `remove( $spec, $version )` deletes named properties. The spec mirrors
159	* the configuration shape: a list of names deletes entries at that level,
160	* and a nested map recurses to prune from within a named value, down to
161	* individual list members.
162	*
163	* A change that declares an unsupported schema version is rejected and does
164	* not alter anything. As with any filter, each callback's return value is
165	* passed to the next callback as `$data`, so callbacks must return the
166	* container they received: a callback that returns nothing, or any other
167	* value, hands that result to every callback hooked at a later priority
168	* instead of the container. Since the write methods return the container,
169	* a callback can end with `return $data->merge( $patch, $version );`.
170	*
171	* @param Gutenberg_View_Config_Data $data The view configuration container
172	* for the entity, exposing the
173	* `default_view`, `default_layouts`,
174	* `view_list`, and `form` keys.
175	* @param array $entity {
176	* The entity the configuration is built for.
177	*
178	* @type string $kind The entity kind.
179	* @type string $name The entity name.
180	* }
181	*/
182	apply_filters(
183	"get_entity_view_config_{$kind}_{$name}",
184	$this,
185	array(
186	'kind' => $kind,
187	'name' => $name,
188	)
189	);
190
191	// Discard any keys the filter introduced that are not part of the
192	// documented configuration shape.
193	return array_intersect_key( $this->get_data(), array_flip( self::CONFIG_KEYS ) );
194	}
195
196	/**
197	* Replaces whole top-level keys, leaving the rest of the configuration alone.
198	*
199	* Like merge() and replace(), set() applies a patch of top-level keys and
200	* touches only the keys the patch names: a key the patch omits keeps whatever
201	* it had, and a `null` value drops the key it names (which resets it to its
202	* default). The difference is depth — where merge() and replace() merge a
203	* named key's value into the current one key by key, set() swaps the whole
204	* value in wholesale, dropping whatever the key held before. A `null` nested
205	* within that value still drops the property it names, so set() honours
206	* nulls at every depth just as merge() and replace() do.
207	*
208	* Use it when a callback owns a key outright and wants to pin it to an exact
209	* shape, without the inherited default leaking through a key-by-key merge.
210	*
211	* A patch that declares an unsupported schema version is rejected and does
212	* not change anything.
213	*
214	* @since 7.1.0
215	*
216	* @param array $patch The partial configuration whose named keys to replace.
217	* @param int $version The schema version the patch was authored against.
218	* @return Gutenberg_View_Config_Data The instance, for chaining.
219	*/
220	public function set( array $patch, int $version ) {
221	return $this->apply( $patch, $version, __METHOD__, 'set' );
222	}
223
224	/**
225	* Removes named properties from the configuration, leaving the rest alone.
226	*
227	* Where merge(), replace(), and set() take a patch of values to write,
228	* remove() takes a spec of names to delete, and its shape mirrors the
229	* configuration it prunes:
230	*
231	* - A list of names deletes each named entry from the value at that level: a
232	* key from an associative array, or the member with a matching identity
233	* (`id`, `slug`, `field`, or a bare scalar) from a list.
234	* - An associative array maps a name to a nested spec, recursing into that
235	* entry's value to delete from within it.
236	*
237	* Naming a top-level configuration key is the one exception: like a `null`
238	* value in a patch, it resets that key to its default rather than dropping it
239	* outright, so top-level removal and top-level `null` compose the same way.
240	*
241	* So `array( 'default_view' )` resets the whole `default_view` key to its
242	* default, `array( 'default_view' => array( 'sort' ) )` drops just its `sort`
243	* property, and `array( 'default_view' => array( 'fields' => array( 'f2' ) ) )`
244	* drops the `f2` member from its `fields` list. A name that is not present is
245	* ignored, and a list is renumbered after a member is removed.
246	*
247	* A spec that declares an unsupported schema version is rejected and does not
248	* change anything.
249	*
250	* @since 7.1.0
251	*
252	* @param array $spec The names to remove, keyed to match the configuration shape.
253	* @param int $version The schema version the spec was authored against.
254	* @return Gutenberg_View_Config_Data The instance, for chaining.
255	*/
256	public function remove( array $spec, int $version ) {
257	if ( $version <= 0 \|\| $version > self::LATEST_VERSION ) {
258	_doing_it_wrong(
259	__METHOD__,
260	esc_html__( 'A view configuration patch must declare a supported schema version.', 'gutenberg' ),
261	'7.1.0'
262	);
263
264	return $this;
265	}
266
267	// A flat list names top-level keys to reset; a map recurses into each
268	// named key to prune from within its value.
269	$spec_is_list = array_is_list( $spec );
270	foreach ( $spec as $spec_key => $spec_value ) {
271	$key = $spec_is_list ? $spec_value : $spec_key;
272
273	if ( ! in_array( $key, self::CONFIG_KEYS, true ) ) {
274	_doing_it_wrong(
275	__METHOD__,
276	sprintf(
277	/* translators: %s: the configuration key. */
278	esc_html__( '"%s" is not a documented view configuration key.', 'gutenberg' ),
279	esc_html( $key )
280	),
281	'7.1.0'
282	);
283	continue;
284	}
285
286	if ( $spec_is_list ) {
287	// Removing a top-level key resets it to its default, just as a
288	// null patch value does.
289	$this->config[ $key ] = $this->defaults[ $key ] ?? array();
290	} elseif ( array_key_exists( $key, $this->config ) ) {
291	$this->config[ $key ] = $this->remove_properties( $this->config[ $key ], $spec_value );
292	}
293	}
294
295	return $this;
296	}
297
298	/**
299	* Replaces list values while merging the rest of a partial configuration.
300	*
301	* Takes the same arguments as merge() and applies the patch the same way,
302	* with one difference: a list in the patch replaces the current list
303	* wholesale instead of merging into it by member identity. Associative
304	* arrays still merge key by key, `null` still drops what it names, and a
305	* scalar still replaces the current value.
306	*
307	* It shouldn't be the default choice — a callback that replaces a list
308	* stops inheriting core's future additions to it — but it's useful when a
309	* contributor needs to pin a list to an exact set of members.
310	*
311	* The shape rule applies here too: a patch value whose shape does not match
312	* the current value — an associative array where a list lives, or a
313	* non-empty list where an associative value lives — is rejected with a
314	* notice and leaves the current value unchanged. An empty array is exempt,
315	* so replacing a list with an empty list still clears it.
316	*
317	* A patch that declares an unsupported schema version is rejected and does
318	* not change anything.
319	*
320	* @since 7.1.0
321	*
322	* @param array $patch The partial configuration to apply.
323	* @param int $version The schema version the patch was authored against.
324	* @return Gutenberg_View_Config_Data The instance, for chaining.
325	*/
326	public function replace( array $patch, int $version ) {
327	return $this->apply( $patch, $version, __METHOD__, 'replace' );
328	}
329
330	/**
331	* Merges a partial configuration into the existing one.
332	*
333	* Applies a patch of top-level keys and touches only the keys the patch
334	* names: a key the patch omits keeps whatever it had, and a `null` value
335	* drops the key it names (which resets it to its default). Each named key's
336	* value is then merged into the current one by value shape:
337	*
338	* - a scalar replaces the current value;
339	* - an associative array merges key by key, with a nested `null` deleting
340	* just the leaf it names;
341	* - a list merges into the current list by member identity.
342	*
343	* Identity is the member's value cast to a string: a bare scalar is its own
344	* identity, and a map is identified by the value of the first of the
345	* well-known identity keys (`id`, `slug`, `field`) it carries. A member
346	* whose identity matches one already present merges into it in place, keeping
347	* its position; a member with no identity is appended to the end of the list.
348	*
349	* For example, given this patch:
350	*
351	* ```php
352	* array(
353	* 'default_view' => array( 'search' => 'new search', 'fields' => array( 'newField' ) ),
354	* 'default_layouts' => array( 'grid' => array( 'layout' => array( 'badgeFields' => array( 'newField' ) ) ) ),
355	* 'view_list' => array( array( 'slug' => 'table', 'title' => 'New title' ) ),
356	* )
357	* ```
358	*
359	* - default_view will be updated so the search string is 'new search' and the newField is appended to the list of fields.
360	* - default_layouts will be updated so that newField is appended to the badgeFields.
361	* - view_list will be updated so that the view with slug 'table' has its title changed to 'New title'.
362	*
363	* A patch value only merges into a current value of the same shape: an
364	* associative array where a list lives, or a non-empty list where an
365	* associative value lives, is rejected with a notice and leaves the current
366	* value unchanged. An empty array merges nothing and is a no-op — clear a
367	* list with replace() and an empty list, or reset a key to its default with
368	* a top-level `null`.
369	*
370	* A patch that declares an unsupported schema version is rejected and does
371	* not change anything.
372	*
373	* @since 7.1.0
374	*
375	* @param array $patch The partial configuration to merge.
376	* @param int $version The schema version the patch was authored against.
377	* @return Gutenberg_View_Config_Data The instance, for chaining.
378	*/
379	public function merge( array $patch, int $version ) {
380	return $this->apply( $patch, $version, __METHOD__, 'merge' );
381	}
382
383	/**
384	* Applies a patch to the configuration, top-level key by top-level key.
385	*
386	* Shared by merge(), replace(), and set(); the three differ only in how the
387	* value of a named key is applied, which is carried by $mode:
388	*
389	* - `merge` merges the value into the current one, lists by member identity;
390	* - `replace` merges the value in the same way but swaps lists wholesale;
391	* - `set` swaps the whole value in wholesale, without merging.
392	*
393	* In every mode a top-level `null` resets the key it names to its default, a
394	* nested `null` drops the property it names, and an omitted key is left
395	* untouched, so all three treat nulls the same way at every depth.
396	*
397	* @since 7.1.0
398	*
399	* @param array $patch The partial configuration to apply.
400	* @param int $version The schema version the patch was authored against.
401	* @param string $method The public method the patch was passed to, for misuse reporting.
402	* @param string $mode How to apply each named key's value: `merge`, `replace`, or `set`.
403	* @return Gutenberg_View_Config_Data The instance, for chaining.
404	*/
405	private function apply( array $patch, int $version, $method, $mode ) {
406	if ( $version <= 0 \|\| $version > self::LATEST_VERSION ) {
407	_doing_it_wrong(
408	esc_html( $method ),
409	esc_html__( 'A view configuration patch must declare a supported schema version.', 'gutenberg' ),
410	'7.1.0'
411	);
412
413	return $this;
414	}
415
416	foreach ( $patch as $key => $value ) {
417	if ( ! in_array( $key, self::CONFIG_KEYS, true ) ) {
418	_doing_it_wrong(
419	esc_html( $method ),
420	sprintf(
421	/* translators: %s: the configuration key. */
422	esc_html__( '"%s" is not a documented view configuration key.', 'gutenberg' ),
423	esc_html( $key )
424	),
425	'7.1.0'
426	);
427	continue;
428	}
429
430	// A null patch value makes the top-level property reset to defaults.
431	if ( null === $value ) {
432	$this->config[ $key ] = $this->defaults[ $key ] ?? array();
433	continue;
434	}
435
436	// set() swaps the whole value in; merge()/replace() merge it into the
437	// current one, differing only in how they treat lists. In every mode a
438	// nested null still drops the property it names.
439	$this->config[ $key ] = 'set' === $mode
440	? $this->strip_nulls( $value )
441	: $this->merge_properties( $this->config[ $key ] ?? array(), $value, 'replace' === $mode );
442	}
443
444	return $this;
445	}
446
447	/**
448	* Recursively drops every property whose value is `null` from a value.
449	*
450	* set() swaps a named key's value in wholesale rather than merging it into
451	* the current one, so it has no existing leaf for a nested `null` to delete
452	* the way merge() and replace() do. Stripping nulls here gives a nested
453	* `null` the same "drop the property it names" meaning under set() that it
454	* carries everywhere else. The same applies to a list replace() swaps in
455	* wholesale. A list is renumbered after a member is removed so removed
456	* entries do not leave gaps.
457	*
458	* @since 7.1.0
459	*
460	* @param mixed $value The value to strip nulls from.
461	* @return mixed The value with every `null` property removed, recursively.
462	*/
463	private function strip_nulls( $value ) {
464	if ( ! is_array( $value ) ) {
465	return $value;
466	}
467
468	$result = array();
469	foreach ( $value as $key => $item ) {
470	// A null value drops the property it names.
471	if ( null === $item ) {
472	continue;
473	}
474
475	$result[ $key ] = $this->strip_nulls( $item );
476	}
477
478	// Renumber a list so a removed member does not leave a gap.
479	return array_is_list( $value ) ? array_values( $result ) : $result;
480	}
481
482	/**
483	* Merges an incoming value into the current one, recursing by value shape.
484	*
485	* This is the core of the merge algorithm and is applied at every nesting
486	* level: a scalar (or `null`) in $incoming replaces $current outright, an
487	* associative array merges key by key (recursing here for each key, with a
488	* `null` value deleting that key), and a list either replaces $current
489	* wholesale ($replace_lists) or merges into it by member identity. The
490	* $replace_lists flag is carried down through associative nesting so that,
491	* under replace(), every list reached along the way is swapped wholesale.
492	*
493	* An array in $incoming only merges into a current value of the same shape.
494	* A non-empty mismatch — an associative array where a list lives, or a
495	* non-empty list where an associative value lives — is reported with
496	* _doing_it_wrong() and leaves the current value unchanged, so a malformed
497	* patch cannot silently destroy configuration. An empty array is
498	* shape-ambiguous and merges nothing, so it is a no-op: clearing a list is
499	* spelled replace() with an empty list, and resetting a key is spelled
500	* `null`.
501	*
502	* @since 7.1.0
503	*
504	* @param mixed $current The current value.
505	* @param mixed $incoming The incoming value.
506	* @param bool $replace_lists Whether a list in $incoming replaces the current list
507	* wholesale instead of merging into it by member identity.
508	* @return mixed The merged value.
509	*/
510	private function merge_properties( $current, $incoming, $replace_lists ) {
511	// Scalar properties are merged as-is.
512	if ( ! is_array( $incoming ) ) {
513	return $incoming;
514	}
515
516	// Numerical indexed arrays are expected to be lists (sequential integer keys starting at 0).
517	if ( array_is_list( $incoming ) ) {
518	// A non-empty list only lands where a list (or nothing) lives, under
519	// merge() and replace() alike. An empty array is shape-ambiguous and
520	// exempt, so replace() with an empty list can still clear a list.
521	if ( array() !== $incoming && is_array( $current ) && ! array_is_list( $current ) && array() !== $current ) {
522	_doing_it_wrong(
523	__METHOD__,
524	esc_html__( 'A view configuration patch value must match the shape of the value it patches: a list merges into a list, and an associative array into an associative array.', 'gutenberg' ),
525	'7.1.0'
526	);
527	return $current;
528	}
529
530	// replace() takes an incoming list as-is; merge() merges it by member identity.
531	if ( $replace_lists ) {
532	// As-is except for nulls: a list swapped in wholesale has no
533	// existing leaf for a null to delete (the same rationale as
534	// set()), so a null member is dropped rather than stored.
535	return $this->strip_nulls( $incoming );
536	}
537
538	// An empty list has no members to merge, and an empty array is
539	// shape-ambiguous, so merging one is a no-op rather than a reset.
540	if ( array() === $incoming ) {
541	return $current;
542	}
543
544	return $this->merge_list_by_identity(
545	is_array( $current ) && array_is_list( $current ) ? $current : array(),
546	$incoming
547	);
548	}
549
550	// Consider any other array as associative (keys are strings).
551	if ( is_array( $current ) && array_is_list( $current ) && array() !== $current ) {
552	_doing_it_wrong(
553	__METHOD__,
554	esc_html__( 'A view configuration patch value must match the shape of the value it patches: a list merges into a list, and an associative array into an associative array.', 'gutenberg' ),
555	'7.1.0'
556	);
557	return $current;
558	}
559
560	$result = is_array( $current ) && ! array_is_list( $current ) ? $current : array();
561	foreach ( $incoming as $key => $value ) {
562	// A null patch value deletes the property.
563	if ( null === $value ) {
564	unset( $result[ $key ] );
565	continue;
566	}
567
568	$result[ $key ] = $this->merge_properties(
569	array_key_exists( $key, $result ) ? $result[ $key ] : array(),
570	$value,
571	$replace_lists
572	);
573	}
574
575	return $result;
576	}
577
578	/**
579	* Removes the properties a spec names from the current value.
580	*
581	* The mirror of merge_properties(), applied at every nesting level: a list in
582	* $spec names entries to delete from $current — associative keys are unset,
583	* and list members are matched by identity (list_item_identity) and dropped —
584	* while an associative $spec recurses into each named entry to prune from
585	* within it. A name absent from $current is ignored, and a list is renumbered
586	* after members are removed so it keeps sequential keys.
587	*
588	* @since 7.1.0
589	*
590	* @param mixed $current The current value.
591	* @param mixed $spec The names to remove from it.
592	* @return mixed The pruned value.
593	*/
594	private function remove_properties( $current, $spec ) {
595	if ( ! is_array( $current ) \|\| ! is_array( $spec ) ) {
596	return $current;
597	}
598
599	$current_is_list = array_is_list( $current );
600
601	if ( array_is_list( $spec ) ) {
602	// Each entry names something to delete from the current value.
603	foreach ( $spec as $name ) {
604	if ( $current_is_list ) {
605	$current = $this->remove_list_member( $current, $name );
606	} else {
607	unset( $current[ $name ] );
608	}
609	}
610	} else {
611	// Each key names an entry to recurse into and prune from within.
612	foreach ( $spec as $name => $subspec ) {
613	if ( $current_is_list ) {
614	foreach ( $current as $index => $member ) {
615	if ( $this->list_item_identity( $member ) === (string) $name ) {
616	$current[ $index ] = $this->remove_properties( $member, $subspec );
617	break;
618	}
619	}
620	} elseif ( array_key_exists( $name, $current ) ) {
621	$current[ $name ] = $this->remove_properties( $current[ $name ], $subspec );
622	}
623	}
624	}
625
626	// Renumber so a list from which a member was removed keeps sequential keys.
627	return $current_is_list ? array_values( $current ) : $current;
628	}
629
630	/**
631	* Removes the first list member matching an identity, leaving the rest.
632	*
633	* @since 7.1.0
634	*
635	* @param array $members The current list.
636	* @param mixed $identity The identity of the member to remove.
637	* @return array The list with the matching member removed, if any.
638	*/
639	private function remove_list_member( array $members, $identity ) {
640	foreach ( $members as $index => $member ) {
641	if ( $this->list_item_identity( $member ) === (string) $identity ) {
642	unset( $members[ $index ] );
643	break;
644	}
645	}
646
647	return $members;
648	}
649
650	/**
651	* Merges an incoming list into the current one by member identity.
652	*
653	* A member of the incoming list whose identity matches one already present
654	* merges into it in place, keeping its position; an unmatched member is
655	* appended to the end, except a literal `null`, which carries no identity
656	* and holds nothing to merge and so is dropped. An appended member has no
657	* existing leaf for a nested `null` to delete (the same rationale as set()),
658	* so its nulls are stripped rather than stored. A matched member's contents
659	* merge recursively with the same rules (merge_properties), so the
660	* identity-aware merge applies at
661	* any nesting level: each key named by the patch is substituted while the
662	* others are left intact, and a list nested inside a member merges by
663	* identity just like the list it lives in.
664	*
665	* @since 7.1.0
666	*
667	* @param array $current The current list.
668	* @param array $incoming The incoming list.
669	* @return array The merged list.
670	*/
671	private function merge_list_by_identity( array $current, array $incoming ) {
672	$result = $current;
673	foreach ( $incoming as $item ) {
674	// A null member carries no identity and holds nothing to merge,
675	// so it is dropped rather than appended as a literal null.
676	if ( null === $item ) {
677	continue;
678	}
679
680	$identity = $this->list_item_identity( $item );
681
682	// Find the index of the existing member with the same identity, if any.
683	// If there's none, append the incoming member to the end of the list.
684	$index = null;
685	if ( null !== $identity ) {
686	foreach ( $result as $i => $existing ) {
687	if ( $this->list_item_identity( $existing ) === $identity ) {
688	$index = $i;
689	break;
690	}
691	}
692	}
693	if ( null === $index ) {
694	// An appended member has no existing leaf for a nested null to
695	// delete, so nulls are dropped rather than stored.
696	$result[] = $this->strip_nulls( $item );
697	continue;
698	}
699
700	// Otherwise, merge the incoming member into the existing one in place.
701	$result[ $index ] = $this->merge_properties( $result[ $index ], $item, false );
702	}
703
704	return $result;
705	}
706
707	/**
708	* Resolves the identity used to match a list member against another.
709	*
710	* The identity is simply the member's value cast to a string, regardless of
711	* which key carries it: a bare scalar is its own identity, and a map is
712	* identified by the value of the first of the well-known identity keys
713	* (`id`, `slug`, `field`) it carries. Because the key is not part of
714	* the identity, a bare field like `'f3'` matches any map carrying that
715	* value, whether it appears as `array( 'id' => 'f3' )`,
716	* `array( 'slug' => 'f3' )`, and so on — this lets the same shorthand target
717	* lists keyed by different fields. Casting to string keeps numeric
718	* identities matching whether they arrive as an int or a string. Anything
719	* else (e.g. a nested list) has no identity and never matches, so it is
720	* always appended.
721	*
722	* @since 7.1.0
723	*
724	* @param mixed $item The list member.
725	* @return string\|null The identity, or null when the member has none.
726	*/
727	private function list_item_identity( $item ) {
728	if ( is_scalar( $item ) ) {
729	return (string) $item;
730	}
731
732	if ( is_array( $item ) && ! array_is_list( $item ) ) {
733	foreach ( array( 'id', 'slug', 'field' ) as $key ) {
734	if ( isset( $item[ $key ] ) && is_scalar( $item[ $key ] ) ) {
735	return (string) $item[ $key ];
736	}
737	}
738	}
739
740	return null;
741	}
742	}
743