Fix reloading in Ruby 3.3

This commit ensures the application is restarted when a preloaded file is changed. This has been silently broken because the fallback behavior still results in the application being restarted, but only when the user next runs a command—hence the acceptance test still passing.

The behavior of BasicSocket#recv changed in Ruby 3.3 such that it now returns nil on a closed stream socket, instead of an empty string. When we call #empty? on nil the NoMethodError is swallowed by the failsafe thread and the application is not restarted.

This commit fixes the issue by checking both #nil? and #empty? so it works with both old and new versions. It also updates the acceptance test to be more specific about what it considers a "reload" by asserting the relevant log line exists.

These logs were produced with a Rails app using Ruby 3.3.5.

bin/spring server
bin/rails test test/some_test.rb
touch config/application.rb

Before

[2024-10-01 17:19:48 +0100] [41338] [watcher:test] check_stale: mtime=1727785028.0366342 < computed=1727799587.8757818
[2024-10-01 17:19:48 +0100] [41338] [watcher:test] marked stale, calling listeners: listeners=[…]
[2024-10-01 17:19:48 +0100] [41338] [application:test] running -> watcher_stale
[2024-10-01 17:19:48 +0100] [41338] [application:test] watcher_stale -> exiting

After

[2024-10-01 17:20:55 +0100] [41375] [watcher:test] check_stale: mtime=1727799587.8757818 < computed=1727799654.9323258
[2024-10-01 17:20:55 +0100] [41375] [watcher:test] marked stale, calling listeners: listeners=[…]
[2024-10-01 17:20:55 +0100] [41375] [application:test] running -> watcher_stale
[2024-10-01 17:20:55 +0100] [41375] [application:test] watcher_stale -> exiting
[2024-10-01 17:20:55 +0100] [41373] [application_manager:test] child 41375 shutdown
[2024-10-01 17:20:55 +0100] [41381] [application:test] preloading app
[2024-10-01 17:20:55 +0100] [41381] [watcher:test] start: poller=nil
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 0 -> 1721481941.5332227
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 1721481941.5332227 -> 1727799654.9323258
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 1727799654.9323258 -> 1727799654.9323258
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 1727799654.9323258 -> 1727799654.9323258
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 1727799654.9323258 -> 1727799654.9323258
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] watcher: add: […]
[2024-10-01 17:20:56 +0100] [41381] [watcher:test] subjects_changed: mtime 1727799654.9323258 -> 1727799654.9323258
[2024-10-01 17:20:56 +0100] [41381] [application:test] initialized -> running

rails / spring

Fix reloading in Ruby 3.3 #730