Add filter to filter Instant Results taxonomy facet terms

.wp-env.json

@@ -29,6 +29,7 @@
         "wp-content/plugins/enable-debug-bar.php": "./tests/cypress/wordpress-files/test-plugins/enable-debug-bar.php",
         "wp-content/plugins/fake-log-messages.php": "./tests/cypress/wordpress-files/test-plugins/fake-log-messages.php",
         "wp-content/plugins/fake-new-activation.php": "./tests/cypress/wordpress-files/test-plugins/fake-new-activation.php",
+        "wp-content/plugins/filter-instant-results-facet-terms.php": "./tests/cypress/wordpress-files/test-plugins/filter-instant-results-facet-terms.php",
         "wp-content/plugins/filter-instant-results-per-page.php": "./tests/cypress/wordpress-files/test-plugins/filter-instant-results-per-page.php",
         "wp-content/plugins/filter-instant-results-args-schema.php": "./tests/cypress/wordpress-files/test-plugins/filter-instant-results-args-schema.php",
         "wp-content/plugins/filter-autosuggest-navigate-callback.php": "./tests/cypress/wordpress-files/test-plugins/filter-autosuggest-navigate-callback.php",

assets/js/instant-results/components/facets/taxonomy-terms-facet.js

@@ -4,6 +4,7 @@
 import { useCallback, useMemo, WPElement } from '@wordpress/element';
 import { decodeEntities } from '@wordpress/html-entities';
 import { __, sprintf } from '@wordpress/i18n';
+import { applyFilters } from '@wordpress/hooks';
 
 /**
  * Internal dependencies.
@@ -81,7 +82,25 @@ export default ({ defaultIsOpen, label, postTypes, name }) => {
 	/**
 	 * Reduce buckets to options.
 	 */
-	const options = useMemo(() => buckets.reduce(reduceOptions, []), [buckets, reduceOptions]);
+	const options = useMemo(() => {
+		/**
+		 * Filter the facet taxonomy terms.
+		 *
+		 * @filter ep.InstantResults.facet.taxonomy.terms
+		 * @since 5.2.0
+		 *
+		 * @param {object[]} terms Taxonomy terms.
+		 * @param {string} name Taxonomy name.
+		 * @param {Array} postTypes Post types label.
+		 * @returns {object[]} Filtered taxonomy terms.
+		 */
+		return applyFilters(
+			'ep.InstantResults.facet.taxonomy.terms',
+			buckets.reduce(reduceOptions, []),
+			name,
+			postTypes,
+		);
+	}, [buckets, reduceOptions, name, postTypes]);
 
 	/**
 	 * Reduce options to labels.

tests/cypress/integration/features/instant-results.cy.js

@@ -439,6 +439,42 @@ describe('Instant Results Feature', { tags: '@slow' }, () => {
 				cy.wait('@apiRequest');
 				cy.url().should('include', 'post_type=product');
 			});
+
+			it('Is possible to filter the taxonomy terms', () => {
+				/**
+				 * Activate test plugin.
+				 */
+				cy.maybeEnableFeature('instant-results');
+				cy.activatePlugin('filter-instant-results-facet-terms', 'wpCli');
+
+				cy.visitAdminPage('admin.php?page=elasticpress');
+				cy.intercept('/wp-json/elasticpress/v1/features*').as('apiRequest');
+
+				cy.contains('button', 'Instant Results').click();
+				cy.get('.components-form-token-field__input').type(
+					'{backspace}{backspace}{backspace}(category){downArrow}{enter}{esc}',
+				);
+				cy.contains('button', 'Save changes').click();
+
+				cy.wait('@apiRequest');
+
+				/**
+				 * Perform a search.
+				 */
+				cy.intercept('*search=block*').as('apiRequest');
+				cy.visit('/');
+				cy.get('.wp-block-search').first().as('searchBlock');
+				cy.get('@searchBlock').find('input[type="search"]').type('block');
+				cy.get('@searchBlock').find('button').click();
+				cy.wait('@apiRequest');
+
+				/**
+				 * The number of terms displayed in the facet should be one.
+				 */
+				cy.get('[id^="ep-search-tax-category-"]').should('have.length', 1);
+
+				cy.deactivatePlugin('filter-instant-results-facet-terms', 'wpCli');
+			});
 		});
 
 		it('Is possible to filter the arguments schema', () => {

tests/cypress/wordpress-files/test-plugins/filter-instant-results-facet-terms.php

@@ -0,0 +1,37 @@
+<?php
+/**
+ * Plugin Name: Filter Instant Results Taxonomy Terms
+ * Description: Filters the Instant Results taxonomy terms for test purposes.
+ * Version:     1.0.0
+ * Author:      10up Inc.
+ * License:     GPLv2 or later
+ *
+ * @package ElasticPress_Tests_E2e
+ */
+
+/**
+ * Limit the Instant Results facet terms to only the "Classic" term.
+ */
+add_action(
+	'wp_footer',
+	function (): void {
+		?>
+		<script>
+			document.addEventListener('DOMContentLoaded', function() {
+				const filterCategoryTerms = (terms, taxonomyName) => {
+
+					if (taxonomyName !== 'tax-category') {
+						return terms;
+					}
+
+					// keep only Term Classic
+					const filteredTerms = terms.filter(term => term.label === 'Classic');
+					return filteredTerms;
+				}
+
+				wp.hooks.addFilter('ep.InstantResults.facet.taxonomy.terms', 'ep-test', filterCategoryTerms);
+			});
+		</script>
+		<?php
+	}
+);