Content Loop Block: Load More option doesn't preserve custom taxonomies argument

[psorensen]

Bug Report: customTaxonomies Not Applied in REST API /articles Endpoint

Summary

The customTaxonomies block attribute is not applied when fetching posts via the /newspack-blocks/v1/articles REST endpoint. The view.php file flattens customTaxonomies into individual taxonomy slug parameters, but these are filtered out by WordPress REST API schema validation before reaching the controller.

Environment

• Plugin: Newspack Blocks
• Affected Files:
  • src/blocks/homepage-articles/view.php (lines 326-337)
  • src/blocks/homepage-articles/class-wp-rest-newspack-articles-controller.php (lines 118-132)
  • includes/class-newspack-blocks.php (lines 619, 677-688)

Steps to Reproduce

1. Create a homepage-articles block with customTaxonomies:

   <!-- wp:newspack-blocks/homepage-articles {"customTaxonomies":[{"slug":"example_taxonomy","terms":["123"]}],"moreButton":true} /-->

2. View the page in the frontend and click the "More" button or trigger pagination

3. Inspect the REST API request URL - it contains example_taxonomy[0]=123 but NOT customTaxonomies

4. In the REST controller, $request->get_params()['customTaxonomies'] is empty

Expected Behavior

The customTaxonomies attribute should be preserved and applied to the WP_Query, filtering posts by the specified custom taxonomy terms.

Actual Behavior

1. customTaxonomies gets flattened into individual taxonomy slug parameters (e.g., example_taxonomy[0]=123)
2. WordPress REST API filters out any parameters not defined in the route args schema
3. get_items() receives an empty customTaxonomies array (default from block.json)
4. Posts are not filtered by custom taxonomy

Root Cause Analysis

Issue 1: In view.php (lines 327-337), when building the REST URL, the code:

• Removes customTaxonomies from attributes
• Flattens it into individual taxonomy slug parameters: $attributes[$tax['slug']] = $tax['terms']
• Builds a URL like ?example_taxonomy[0]=123 instead of preserving customTaxonomies

Issue 2: The REST endpoint registers args via get_attribute_schema() which only includes block.json attributes. Dynamic taxonomy slugs (like example_taxonomy) are not in the schema.

Issue 3: WordPress REST API's sanitize_params() method (line 834 of wp-includes/rest-api/class-wp-rest-request.php) skips parameters not in the registered args:

if ( ! isset( $attributes['args'][ $key ] ) ) {
    continue;
}

Issue 4: build_articles_query() (line 619) only checks $attributes['customTaxonomies'] and doesn't look for flattened taxonomy parameters.

Code References

• view.php:327-337 - Flattens customTaxonomies for REST URL
• class-wp-rest-newspack-articles-controller.php:45 - Registers route with get_attribute_schema()
• class-wp-rest-newspack-articles-controller.php:122-125 - Merges params, customTaxonomies defaults to empty array
• class-newspack-blocks.php:619 - Only checks $attributes['customTaxonomies'], doesn't handle flattened params

Workaround

Intercept rest_pre_dispatch to reconstruct customTaxonomies from raw query parameters:

add_filter( 'rest_pre_dispatch', function( $result, $server, $request ) {
    if ( '/newspack-blocks/v1/articles' !== $request->get_route() ) {
        return $result;
    }

    $raw_params = $request->get_query_params();
    $custom_taxonomies = [];
    $registered_taxonomies = get_taxonomies( [ 'public' => true ], 'objects' );
    
    foreach ( $registered_taxonomies as $taxonomy ) {
        if ( isset( $raw_params[ $taxonomy->name ] ) ) {
            $terms = $raw_params[ $taxonomy->name ];
            if ( ! is_array( $terms ) ) {
                $terms = [ $terms ];
            }
            $terms = array_filter( array_map( 'intval', $terms ) );
            if ( ! empty( $terms ) ) {
                $custom_taxonomies[] = [
                    'slug'  => $taxonomy->name,
                    'terms' => array_values( $terms ),
                ];
            }
        }
    }
    
    if ( ! empty( $custom_taxonomies ) ) {
        $request->set_param( 'customTaxonomies', $custom_taxonomies );
    }
    
    return $result;
}, 10, 3 );

Suggested Fix

Option 1 (Recommended): Modify view.php to preserve customTaxonomies in the REST URL

• Keep customTaxonomies in the attributes array when building the REST URL
• Ensure it's properly serialized for URL query strings (e.g., JSON encoding)

Option 2: Modify get_items() in the REST controller

• Check for flattened taxonomy parameters in $request->get_params()
• Reconstruct customTaxonomies before calling build_articles_query()

Option 3: Modify build_articles_query()

• Check for individual taxonomy slug parameters in $attributes
• Convert them to tax_query entries if customTaxonomies is empty

Additional Notes

• This affects any pagination or "More" button functionality that relies on the REST endpoint
• Initial server-side rendering works correctly because it calls build_articles_query() directly with the full attributes array
• Only affects the /articles endpoint; the /newspack-blocks-posts endpoint may not have this issue if it handles attributes differently

Priority

High - Custom taxonomy filtering is completely broken for paginated/fetched results via REST API.