From 1109637befb73b223512dc0ba15105f7a8f002c9 Mon Sep 17 00:00:00 2001
From: Nicolas Lemoine <nico.lemoine@gmail.com>
Date: Tue, 23 Mar 2021 21:51:53 +0100
Subject: [PATCH] Allow extending taxonomy

---
 src/Taxonomy.php | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/Taxonomy.php b/src/Taxonomy.php
index 3e8b958..b2c6230 100644
--- a/src/Taxonomy.php
+++ b/src/Taxonomy.php
@@ -3,6 +3,8 @@
 
 namespace ExtCPTs;
 
+use WP_Taxonomy;
+
 class Taxonomy {
 
 	/**
@@ -197,8 +199,14 @@ public function init(): void {
 			add_filter( 'rewrite_testing_tests', [ $this, 'rewrite_testing_tests' ], 1 );
 		}
 
-		# Register taxonomy:
-		$this->register_taxonomy();
+		$existing = get_taxonomy( $this->taxonomy );
+
+		if ( empty( $existing ) ) {
+			# Register taxonomy:
+			$this->register_taxonomy();
+		} else {
+			$this->extend( $existing );
+		}
 
 		/**
 		 * Fired when the extended taxonomy instance is set up.
@@ -210,6 +218,23 @@ public function init(): void {
 		do_action( "ext-taxos/{$this->taxonomy}/instance", $this );
 	}
 
+	/**
+	 * Extends an existing taxonomy object. Currently only handles labels.
+	 *
+	 * @param WP_Taxonomy $taxonomy A taxonomy object.
+	 */
+	public function extend( WP_Taxonomy $taxonomy ): void {
+		# Merge core with overridden labels
+		$this->args['labels'] = array_merge( (array) get_taxonomy_labels( $taxonomy ), $this->args['labels'] );
+
+		$GLOBALS['wp_taxonomies'][ $taxonomy->name ]->labels = (object) $this->args['labels'];
+
+		// Register taxonomy for object types
+		foreach ( $this->object_type as $object_type ) {
+			register_taxonomy_for_object_type( $this->taxonomy, $object_type );
+		}
+	}
+
 	/**
 	 * Add our rewrite tests to the Rewrite Rule Testing tests array.
 	 *