Taxonomy: Check for empty term after DB sanitization in wp_insert_term().

When inserting a new term in the database, `wp_insert_term()` will check if the term is empty and return a corresponding error.

Afterwards the term is sanitized and inserted in the database. However, there is a chance the term is empty after the DB sanitization.

This commit adds a check for an empty term name after the term is sanitized, returning an error in that case.

Follow-up to [5726], [8393].

Props fgiannar, kraftbj.
Fixes #59995.

git-svn-id: https://develop.svn.wordpress.org/trunk@57251 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/taxonomy.php

@@ -2434,6 +2434,11 @@ function wp_insert_term( $term, $taxonomy, $args = array() ) {
 	$description = wp_unslash( $args['description'] );
 	$parent      = (int) $args['parent'];
 
+	// Sanitization could clean the name to an empty string that must be checked again.
+	if ( '' === $name ) {
+		return new WP_Error( 'invalid_term_name', __( 'Invalid term name.' ) );
+	}
+
 	$slug_provided = ! empty( $args['slug'] );
 	if ( ! $slug_provided ) {
 		$slug = sanitize_title( $name );

tests/phpunit/tests/term/wpInsertTerm.php

@@ -895,6 +895,19 @@ class Tests_Term_WpInsertTerm extends WP_UnitTestCase {
 		$this->assertSame( '', $term_object->description );
 	}
 
+	/**
+	 * @ticket 59995
+	 */
+	public function test_wp_insert_term_with_empty_name_after_db_sanitization() {
+		$term = wp_insert_term(
+			'<script>onclick=alert("hello")</script>',
+			'post_tag'
+		);
+
+		$this->assertWPError( $term );
+		$this->assertSame( 'invalid_term_name', $term->get_error_code() );
+	}
+
 	/** Helpers */
 
 	public function deleted_term_cb( $term, $tt_id, $taxonomy, $deleted_term, $object_ids ) {