Keep reader replies out of the comments feed

.github/changelog/fix-reader-comments-feed

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Replies to posts from accounts you follow no longer show up in your comments feed and comment widgets.

includes/class-comment.php

@@ -29,6 +29,7 @@ public static function init() {
 		\add_filter( 'comment_reply_link', array( self::class, 'comment_reply_link' ), 10, 3 );
 		\add_filter( 'comment_class', array( self::class, 'comment_class' ), 10, 3 );
 		\add_filter( 'comment_feed_where', array( static::class, 'comment_feed_where' ) );
+		\add_filter( 'widget_comments_args', array( static::class, 'widget_comments_args' ) );
 		\add_filter( 'get_comment_link', array( self::class, 'remote_comment_link' ), 11, 2 );
 		\add_action( 'pre_get_comments', array( static::class, 'comment_query' ) );
 		\add_filter( 'get_page_of_comment_query_args', array( static::class, 'get_page_of_comment_query_args' ) );
@@ -435,7 +436,8 @@ public static function comment_class( $classes, $css_class, $comment_id ) {
 	/**
 	 * Makes the comment feed filterable by comment type.
 	 *
-	 * Also excludes ActivityPub comment types from the feed when no type is specified.
+	 * Also excludes ActivityPub comment types from the feed when no type is specified,
+	 * and replies to remote posts in any case.
 	 *
 	 * @param string $where The `WHERE` clause for the comment feed query.
 	 *
@@ -444,6 +446,14 @@ public static function comment_class( $classes, $css_class, $comment_id ) {
 	public static function comment_feed_where( $where ) {
 		global $wpdb;
 
+		// Replies to remote posts belong to the reader, not to the site's comments.
+		$hide_for = self::hide_for();
+		if ( $hide_for ) {
+			$placeholders = \implode( ', ', \array_fill( 0, \count( $hide_for ), '%s' ) );
+			// phpcs:ignore WordPress.DB.PreparedSQLPlaceholders.ReplacementsWrongNumber, WordPress.DB.PreparedSQL.NotPrepared
+			$where .= $wpdb->prepare( \sprintf( " AND {$wpdb->comments}.comment_post_ID NOT IN ( SELECT ID FROM {$wpdb->posts} WHERE post_type IN (%s) )", $placeholders ), ...$hide_for );
+		}
+
 		$comment_type = \get_query_var( 'type' );
 
 		if ( 'all' === $comment_type ) {
@@ -463,6 +473,26 @@ public static function comment_feed_where( $where ) {
 		return $where;
 	}
 
+	/**
+	 * Keeps replies to remote posts out of the Recent Comments widget and the Latest Comments block.
+	 *
+	 * @since unreleased
+	 *
+	 * @param array $args The comment query arguments.
+	 *
+	 * @return array The filtered arguments.
+	 */
+	public static function widget_comments_args( $args ) {
+		$hide_for = self::hide_for();
+
+		// The comment query has no `post_type__not_in`, so list every other post type.
+		if ( $hide_for && empty( $args['post_type'] ) ) {
+			$args['post_type'] = \array_values( \array_diff( \get_post_types(), $hide_for ) );
+		}
+
+		return $args;
+	}
+
 	/**
 	 * Gets the public comment id via the WordPress comments meta.
 	 *

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

@@ -872,6 +872,45 @@ public function test_comment_feed_where() {
 		\set_query_var( 'type', null );
 	}
 
+	/**
+	 * Replies to remote posts stay out of the comments feed and the comment widgets.
+	 *
+	 * @covers ::comment_feed_where
+	 * @covers ::widget_comments_args
+	 */
+	public function test_remote_post_replies_stay_out_of_public_lists() {
+		// Comments on post types without comment support stay in the lists.
+		\register_post_type( 'no_comment_support', array( 'supports' => array( 'title' ) ) );
+
+		$comment_ids = array();
+		foreach ( array( 'post', 'no_comment_support', Remote_Posts::POST_TYPE ) as $post_type ) {
+			$comment_ids[ $post_type ] = self::factory()->comment->create(
+				array(
+					'comment_approved' => '1',
+					'comment_post_ID'  => self::factory()->post->create( array( 'post_type' => $post_type ) ),
+				)
+			);
+		}
+		$expected = array( (string) $comment_ids['post'], (string) $comment_ids['no_comment_support'] );
+
+		foreach ( array( null, 'all' ) as $type ) {
+			\set_query_var( 'type', $type );
+			$query = new \WP_Query(
+				array(
+					'feed'         => 'comments-rss2',
+					'withcomments' => true,
+				)
+			);
+			$this->assertEqualSets( $expected, \wp_list_pluck( $query->comments, 'comment_ID' ) );
+		}
+		\set_query_var( 'type', null );
+
+		$args = \apply_filters( 'widget_comments_args', array( 'post_status' => 'publish' ), array() );
+		$this->assertEqualSets( $expected, \wp_list_pluck( \get_comments( $args ), 'comment_ID' ) );
+
+		\unregister_post_type( 'no_comment_support' );
+	}
+
 	/**
 	 * Test that comments on ap_post are excluded from admin comment queries.
 	 *