Fix map_meta_cap notice by deferring migration until post types are registered

.github/changelog/fix-3332-migration-cpt-order

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Fixed a warning that could appear when the plugin was activated or updated.

includes/class-migration.php

@@ -26,7 +26,15 @@ class Migration {
 	 * Initialize the class, registering WordPress hooks.
 	 */
 	public static function init() {
-		self::maybe_migrate();
+		/*
+		 * Priority 15: after `register_extra_fields_post_types` at 11 (so the
+		 * `ap_extrafield` / `ap_extrafield_blog` post types exist when the
+		 * initial migration inserts the default "Powered by" field) and before
+		 * the rewrite flush below at priority 20. If you renumber one, renumber
+		 * the other, a callback added to the same priority bucket during its
+		 * own dispatch does not run for that dispatch.
+		 */
+		\add_action( 'init', array( self::class, 'maybe_migrate' ), 15 );
 
 		Scheduler::register_async_batch_callback( 'activitypub_migrate_from_0_17', array( self::class, 'migrate_from_0_17' ) );
 		Scheduler::register_async_batch_callback( 'activitypub_update_comment_counts', array( self::class, 'update_comment_counts' ) );
@@ -226,10 +234,10 @@ public static function maybe_migrate() {
 		}
 
 		/*
-		 * Defer the flush to late in the `init` cycle (priority 20). Migration::init
-		 * runs at priority 1, which is earlier than most plugins register their
-		 * rewrite rules. Flushing synchronously here would persist a truncated
-		 * ruleset that omits third-party rules added on `init` at priority 10.
+		 * Defer the flush to late in the `init` cycle (priority 20), after the
+		 * priority-10 crowd that registers most plugin rewrite rules. Flushing
+		 * synchronously here would persist a truncated ruleset that omits
+		 * third-party rules added on `init` at priority 10.
 		 */
 		\add_action( 'init', array( Activitypub::class, 'flush_rewrite_rules' ), 20 );
 

tests/phpunit/tests/includes/class-test-migration.php

@@ -16,6 +16,7 @@
 use Activitypub\Collection\Remote_Actors;
 use Activitypub\Comment;
 use Activitypub\Migration;
+use Activitypub\Post_Types;
 use Activitypub\Scheduler;
 use Activitypub\Tombstone;
 
@@ -633,6 +634,33 @@ public function mock_webfinger() {
 		);
 	}
 
+	/**
+	 * Regression guard: Migration::init() must register maybe_migrate() on
+	 * `init` at a priority strictly greater than the priority used by
+	 * Post_Types::register_extra_fields_post_types() (11), so the
+	 * `ap_extrafield` / `ap_extrafield_blog` post types exist when the
+	 * fresh-install migration inserts the default "Powered by" field (see
+	 * #3332). This pins the hook-ordering contract, it does not by itself
+	 * prove the `map_meta_cap` `_doing_it_wrong` notice is gone.
+	 *
+	 * @covers ::init
+	 */
+	public function test_init_defers_migration_past_post_type_registration() {
+		$migration_priority          = \has_action( 'init', array( Migration::class, 'maybe_migrate' ) );
+		$cpt_registration_callback   = array( Post_Types::class, 'register_extra_fields_post_types' );
+		$cpt_registration_priority   = \has_action( 'init', $cpt_registration_callback );
+
+		$this->assertNotFalse( $migration_priority, 'Migration::init() must register maybe_migrate() on init.' );
+		$this->assertNotFalse( $cpt_registration_priority, 'Extra-fields CPT registration must be hooked on init.' );
+
+		$this->assertIsInt( $migration_priority, 'maybe_migrate() must be registered with a numeric priority.' );
+		$this->assertGreaterThan(
+			(int) $cpt_registration_priority,
+			(int) $migration_priority,
+			'Migration must run after the extra-fields post types are registered.'
+		);
+	}
+
 	/**
 	 * Test add_default_extra_field.
 	 */