Taxonomy: Add 'pre_get_term_by' filter to short-circuit get_term_by()

src/wp-includes/taxonomy.php

@@ -1098,6 +1098,25 @@ function get_term( $term, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
  */
 function get_term_by( $field, $value, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
 
+	/**
+	 * Get all Term data from database by Term field and data.
+	 *
+	 * This allows one to short-circuit the default logic, perhaps by
+	 * replacing it with a routine that is more optimal for your setup.
+	 *
+	 * @since TBD
+	 *
+	 * @param string     $field    Either 'slug', 'name', 'id' (term_id), or 'term_taxonomy_id'
+	 * @param string|int $value    Search for this term value
+	 * @param string     $taxonomy Taxonomy name. Optional, if `$field` is 'term_taxonomy_id'.
+	 * @param string     $output   Constant OBJECT, ARRAY_A, or ARRAY_N
+	 * @param string     $filter   Optional, default is raw or no WordPress defined filter will applied.
+	 */
+	$pre = apply_filters( 'pre_get_term_by', null, $field, $value, $taxonomy, $output, $filter );
+	if ( null !== $pre ) {
+		return $pre;
+	}
+
 	// 'term_taxonomy_id' lookups don't require taxonomy checks.
 	if ( 'term_taxonomy_id' !== $field && ! taxonomy_exists( $taxonomy ) ) {
 		return false;

tests/phpunit/tests/term/getTermBy.php

@@ -58,6 +58,23 @@ public function test_get_term_by_unknown() {
 		$this->assertFalse( $term2 );
 	}
 
+	/**
+	 * @ticket 36978
+	 */
+	public function test_get_term_by_pre_filter() {
+		add_filter( 'pre_get_term_by', array( $this, 'filter_pre_get_term_by' ) );
+
+		$term = get_term_by( 'slug', 'foo', 'category' );
+
+		remove_filter( 'pre_get_term_by', array( $this, 'filter_pre_get_term_by' ) );
+
+		$this->assertSame( 'short-circuited', $term );
+	}
+
+	public function filter_pre_get_term_by() {
+		return 'short-circuited';
+	}
+
 	/**
 	 * @ticket 33281
 	 */