Posts, Post Types: Bail early in _reset_front_page_settings_for_post() when the post no longer exists

src/wp-includes/ms-blogs.php

@@ -872,6 +872,10 @@ function _update_blog_date_on_post_publish( $new_status, $old_status, $post ) {
 function _update_blog_date_on_post_delete( $post_id ) {
 	$post = get_post( $post_id );
 
+	if ( ! $post ) {
+		return;
+	}
+
 	$post_type_obj = get_post_type_object( $post->post_type );
 	if ( ! $post_type_obj || ! $post_type_obj->public ) {
 		return;

src/wp-includes/post.php

@@ -4226,6 +4226,10 @@ function wp_delete_post( $post_id = 0, $force_delete = false ) {
 function _reset_front_page_settings_for_post( $post_id ) {
 	$post = get_post( $post_id );
 
+	if ( ! $post ) {
+		return;
+	}
+
 	if ( 'page' === $post->post_type ) {
 		/*
 		 * If the page is defined in option page_on_front or post_for_posts,

tests/phpunit/tests/post/wpDeletePost.php

@@ -206,4 +206,29 @@ public function test_wp_delete_post_reassigns_attachments_to_parent() {
 
 		$this->assertSame( $parent_post_id, get_post( $attachment_id )->post_parent );
 	}
+
+	/**
+	 * Tests that wp_delete_post() does not trigger a warning when the post is deleted
+	 * by another process while it is being deleted.
+	 *
+	 * The concurrent delete is simulated by deleting the post from a `before_delete_post`
+	 * callback that runs before `_reset_front_page_settings_for_post()`.
+	 *
+	 * @ticket 66684
+	 *
+	 * @covers ::_reset_front_page_settings_for_post
+	 */
+	public function test_wp_delete_post_handles_post_deleted_concurrently() {
+		$post_id = self::factory()->post->create();
+
+		$delete_concurrently = static function ( $post_id_being_deleted ) use ( &$delete_concurrently ) {
+			remove_action( 'before_delete_post', $delete_concurrently, 1 );
+			wp_delete_post( $post_id_being_deleted, true );
+		};
+		add_action( 'before_delete_post', $delete_concurrently, 1 );
+
+		wp_delete_post( $post_id, true );
+
+		$this->assertNull( get_post( $post_id ) );
+	}
 }