Taxonomy: Add support for default terms for custom taxonomies.

The new default_term argument is added to `register_taxonomy()` allowing a user to define the default term `name` and optionally `slug` and `description`. 

Fixes #43517.

Props enrico.sorcinelli, SergeyBiryukov, desrosj, davidbaumwald, whyisjake.


Built from https://develop.svn.wordpress.org/trunk@48356


git-svn-id: http://core.svn.wordpress.org/trunk@48125 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/capabilities.php

@@ -539,7 +539,7 @@ function map_meta_cap( $cap, $user_id, ...$args ) {
 				break;
 			}
 
-			if ( 'delete_term' === $cap && ( get_option( 'default_' . $term->taxonomy ) == $term->term_id ) ) {
+			if ( 'delete_term' === $cap && ( get_option( 'default_' . $term->taxonomy ) == $term->term_id || get_option( 'default_taxonomy_' . $term->taxonomy ) == $term->term_id ) ) {
 				$caps[] = 'do_not_allow';
 				break;
 			}

wp-includes/class-wp-taxonomy.php

@@ -209,6 +209,15 @@ final class WP_Taxonomy {
 	 */
 	public $rest_controller_class;
 
+	/**
+	 * The default term name for this taxonomy. If you pass an array you have
+	 * to set 'name' and optionally 'slug' and 'description'.
+	 *
+	 * @since 5.5.0
+	 * @var array|string
+	 */
+	public $default_term;
+
 	/**
 	 * The controller instance for this taxonomy's REST API endpoints.
 	 *
@@ -288,6 +297,7 @@ final class WP_Taxonomy {
 			'show_in_rest'          => false,
 			'rest_base'             => false,
 			'rest_controller_class' => false,
+			'default_term'          => null,
 			'_builtin'              => false,
 		);
 
@@ -386,6 +396,21 @@ final class WP_Taxonomy {
 			}
 		}
 
+		// Default taxonomy term.
+		if ( ! empty( $args['default_term'] ) ) {
+			if ( ! is_array( $args['default_term'] ) ) {
+				$args['default_term'] = array( 'name' => $args['default_term'] );
+			}
+			$args['default_term'] = wp_parse_args(
+				$args['default_term'],
+				array(
+					'name'        => '',
+					'slug'        => '',
+					'description' => '',
+				)
+			);
+		}
+
 		foreach ( $args as $property_name => $property_value ) {
 			$this->$property_name = $property_value;
 		}

wp-includes/post.php

@@ -4033,6 +4033,15 @@ function wp_insert_post( $postarr, $wp_error = false ) {
 		wp_set_post_tags( $post_ID, $postarr['tags_input'] );
 	}
 
+	// Add default term for all associated custom taxonomies.
+	if ( 'auto-draft' !== $post_status ) {
+		foreach ( get_object_taxonomies( $post_type, 'object' ) as $taxonomy => $tax_object ) {
+			if ( ! empty( $tax_object->default_term ) && ( empty( $postarr['tax_input'] ) || ! isset( $postarr['tax_input'][ $taxonomy ] ) ) ) {
+				$postarr['tax_input'][ $taxonomy ] = array();
+			}
+		}
+	}
+
 	// New-style support for all custom taxonomies.
 	if ( ! empty( $postarr['tax_input'] ) ) {
 		foreach ( $postarr['tax_input'] as $taxonomy => $tags ) {

wp-includes/taxonomy.php

@@ -335,6 +335,7 @@ function is_taxonomy_hierarchical( $taxonomy ) {
  *              arguments to register the Taxonomy in REST API.
  * @since 5.1.0 Introduced `meta_box_sanitize_cb` argument.
  * @since 5.4.0 Added the registered taxonomy object as a return value.
+ * @since 5.5.0 Introduced `default_term` argument.
  *
  * @global array $wp_taxonomies Registered taxonomies.
  *
@@ -406,6 +407,13 @@ function is_taxonomy_hierarchical( $taxonomy ) {
  *                                                to post types, which confirms that the objects are published before
  *                                                counting them. Default _update_generic_term_count() for taxonomies
  *                                                attached to other object types, such as users.
+ *     @type string|array  $default_term {
+ *         Default term to be used for the taxonomy.
+ *
+ *         @type string $name         Name of default term.
+ *         @type string $slug         Slug for default term. Default empty.
+ *         @type string $description  Description for default term. Default empty.
+ *     }
  *     @type bool          $_builtin              This taxonomy is a "built-in" taxonomy. INTERNAL USE ONLY!
  *                                                Default false.
  * }
@@ -432,6 +440,27 @@ function register_taxonomy( $taxonomy, $object_type, $args = array() ) {
 
 	$taxonomy_object->add_hooks();
 
+	// Add default term.
+	if ( ! empty( $taxonomy_object->default_term ) ) {
+		if ( $term = term_exists( $taxonomy_object->default_term['name'], $taxonomy ) ) {
+			update_option( 'default_taxonomy_' . $taxonomy_object->name, $term['term_id'] );
+		} else {
+			$term = wp_insert_term(
+				$taxonomy_object->default_term['name'],
+				$taxonomy,
+				array(
+					'slug'        => sanitize_title( $taxonomy_object->default_term['slug'] ),
+					'description' => $taxonomy_object->default_term['description'],
+				)
+			);
+
+			// Update term id in options.
+			if ( ! is_wp_error( $term ) ) {
+				update_option( 'default_taxonomy_' . $taxonomy_object->name, $term['term_id'] );
+			}
+		}
+	}
+
 	/**
 	 * Fires after a taxonomy is registered.
 	 *
@@ -2482,6 +2511,14 @@ function wp_set_object_terms( $object_id, $terms, $taxonomy, $append = false ) {
 		$terms = array( $terms );
 	}
 
+	// Add default term.
+	$taxonomy_obj = get_taxonomy( $taxonomy );
+
+	// Default term for this taxonomy.
+	if ( empty( $terms ) && ! empty( $taxonomy_obj->default_term ) && ! empty( $default_term_id = get_option( 'default_taxonomy_' . $taxonomy ) ) ) {
+		$terms[] = (int) $default_term_id;
+	}
+
 	if ( ! $append ) {
 		$old_tt_ids = wp_get_object_terms(
 			$object_id,

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-48355';
+$wp_version = '5.5-alpha-48356';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.