[jorgefilipecosta]

Follow up to https://core.trac.wordpress.org/changeset/64592 and #14139.

Depends on #14671, whose commit is the first one here.

What

• The run endpoint prepares every result for JSON clients with wp_prepare_json_value_for_client(), not only associative arrays. An empty array returned for an object output schema is now encoded as {} at the root, in lists, and inside object or JsonSerializable results, instead of [], which the JS client (executeAbility()) rejected with ability_invalid_output. This fixes it for all abilities, e.g. core/settings-get when no setting matches.
• Arrays stay arrays: an empty list or a list of strings is still encoded as [].
• The run handler sets allow_fields, allow_embed and allow_links to false (from REST API: Allow routes to disable _fields, _embed and response links #14671), so _fields, _embed and response links leave the result unchanged, and it follows the ability's output schema whether it is an object, an array, or a scalar value.

await wp.apiFetch( { path: wp.url.addQueryArgs( '/wp-abilities/v1/abilities/core/settings-get/run', { input: { group: 'writing', fields: [ 'title' ] } } ) } );
// Before: []
// After:  {}

await wp.apiFetch( { path: wp.url.addQueryArgs( '/wp-abilities/v1/abilities/core/settings-get/run', { input: { group: 'writing', fields: [ 'title' ] }, _fields: 'title' } ) } );
// After:  {}

Issue found while testing the query abilities through the JS client; the fix was drafted with AI assistance and reviewed by me.

Trac ticket: https://core.trac.wordpress.org/ticket/66267

Testing

Verify unit tests are passing:

npm run test:php -- --filter 'test_output_is_prepared_for_json_clients|test_no_matching_setting_is_encoded_as_an_empty_object'

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props jorgefilipecosta, gziolo.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[gziolo]

I noted in #14139 that we should follow-up and figure out how to map [] to {} in a way that doesn't break REST API handler when global handlers like _fields or _links get passed. Casting to (object) in the ability doesn't resolve the problem.

[jorgefilipecosta]

I noted in #14139 that we should follow-up and figure out how to map [] to {} in a way that doesn't break REST API handler when global handlers like _fields or _links get passed. Casting to (object) in the ability doesn't resolve the problem.

Hi @gziolo this PR was updated and addressed these issues.

[gziolo]

Could we let controllers explicitly opt out of _fields filtering, _embed processing, and response link injection?

The problem extends beyond objects to scalar values, where these transformations have no meaningful application. Currently, _fields can trigger a type error, embedding silently does nothing, and link injection can fail or change the response’s type. Broadening array-specific helpers to accept arbitrary values doesn’t establish consistent support for these features.

The ability execution controller could disable all three explicitly, preserving the ability’s output schema and making behavior predictable regardless of whether the result is an object, array, or scalar.

[jorgefilipecosta]

Could we let controllers explicitly opt out of _fields filtering, _embed processing, and response link injection?

Hi @gziolo, Currently there is no way to opt out, following your feedback I'm proposing it at #14671.