Backport should_compact change from Gutenberg

WordPress/gutenberg#75682

Author: chriszarate

src/wp-includes/collaboration/class-wp-http-polling-sync-server.php

@@ -457,8 +457,8 @@ private function add_update( string $room, int $client_id, string $type, string
 	 * @param int    $cursor       Return updates after this cursor.
 	 * @param bool   $is_compactor True if this client is nominated to perform compaction.
 	 * @return array{
-	 *   compaction_request: array|null,
 	 *   end_cursor: int,
+	 *   should_compact: bool,
 	 *   room: string,
 	 *   total_updates: int,
 	 *   updates: array<int, array{data: string, type: string}>
@@ -481,18 +481,14 @@ private function get_updates( string $room, int $client_id, int $cursor, bool $i
 			);
 		}
 
-		// Determine if this client should perform compaction.
-		$compaction_request = null;
-		if ( $is_compactor && $total_updates > self::COMPACTION_THRESHOLD ) {
-			$compaction_request = $updates_after_cursor;
-		}
+		$should_compact = $is_compactor && $total_updates > self::COMPACTION_THRESHOLD;
 
 		return array(
-			'compaction_request' => $compaction_request,
-			'end_cursor'         => $this->storage->get_cursor( $room ),
-			'room'               => $room,
-			'total_updates'      => $total_updates,
-			'updates'            => $typed_updates,
+			'end_cursor'     => $this->storage->get_cursor( $room ),
+			'room'           => $room,
+			'should_compact' => $should_compact,
+			'total_updates'  => $total_updates,
+			'updates'        => $typed_updates,
 		);
 	}
 }

tests/phpunit/tests/rest-api/rest-sync-server.php

@@ -285,7 +285,7 @@ public function test_sync_response_structure() {
 		$this->assertArrayHasKey( 'updates', $room_data );
 		$this->assertArrayHasKey( 'end_cursor', $room_data );
 		$this->assertArrayHasKey( 'total_updates', $room_data );
-		$this->assertArrayHasKey( 'compaction_request', $room_data );
+		$this->assertArrayHasKey( 'should_compact', $room_data );
 	}
 
 	public function test_sync_response_room_matches_request() {
@@ -536,6 +536,97 @@ public function test_sync_total_updates_increments() {
 		$this->assertSame( 3, $data['rooms'][0]['total_updates'] );
 	}
 
+	/*
+	 * Compaction tests.
+	 */
+
+	public function test_sync_should_compact_is_false_below_threshold() {
+		wp_set_current_user( self::$editor_id );
+
+		$room   = $this->get_post_room();
+		$update = array(
+			'type' => 'update',
+			'data' => 'dGVzdA==',
+		);
+
+		// Client 1 sends a single update.
+		$response = $this->dispatch_sync(
+			array(
+				$this->build_room( $room, 1, 0, array( 'user' => 'c1' ), array( $update ) ),
+			)
+		);
+
+		$data = $response->get_data();
+		$this->assertFalse( $data['rooms'][0]['should_compact'] );
+	}
+
+	public function test_sync_should_compact_is_true_above_threshold_for_compactor() {
+		wp_set_current_user( self::$editor_id );
+
+		$room    = $this->get_post_room();
+		$updates = array();
+		for ( $i = 0; $i < 51; $i++ ) {
+			$updates[] = array(
+				'type' => 'update',
+				'data' => base64_encode( "update-$i" ),
+			);
+		}
+
+		// Client 1 sends enough updates to exceed the compaction threshold.
+		$this->dispatch_sync(
+			array(
+				$this->build_room( $room, 1, 0, array( 'user' => 'c1' ), $updates ),
+			)
+		);
+
+		// Client 2 (lowest connected client) should be told to compact.
+		$response = $this->dispatch_sync(
+			array(
+				$this->build_room( $room, 2, 0, array( 'user' => 'c2' ) ),
+			)
+		);
+
+		$data = $response->get_data();
+		$this->assertTrue( $data['rooms'][0]['should_compact'] );
+	}
+
+	public function test_sync_should_compact_is_false_for_non_compactor() {
+		wp_set_current_user( self::$editor_id );
+
+		$room    = $this->get_post_room();
+		$updates = array();
+		for ( $i = 0; $i < 51; $i++ ) {
+			$updates[] = array(
+				'type' => 'update',
+				'data' => base64_encode( "update-$i" ),
+			);
+		}
+
+		// Client 1 sends enough updates to exceed the compaction threshold.
+		$this->dispatch_sync(
+			array(
+				$this->build_room( $room, 1, 0, array( 'user' => 'c1' ), $updates ),
+			)
+		);
+
+		// Connect client 2 (lower ID) so client 3 is not the compactor.
+		$this->dispatch_sync(
+			array(
+				$this->build_room( $room, 2, 0, array( 'user' => 'c2' ) ),
+			)
+		);
+
+		// Client 3 (higher ID) should not be told to compact.
+		$response = $this->dispatch_sync(
+			array(
+				$this->build_room( $room, 3, 0, array( 'user' => 'c3' ) ),
+			)
+		);
+
+		$data = $response->get_data();
+		$this->assertFalse( $data['rooms'][0]['should_compact'] );
+	}
+
 	/*
 	 * Awareness tests.
 	 */