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 [1] 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.

[1]: ruby/ruby#6407

Author: thomasmarshall

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Next Release
 
+* Fix reloading issue in Ruby 3.3.
+
 ## 4.2.1
 
 * Added `Spring.connect_timeout` and `Spring.boot_timeout` to allow to increase timeout for larger apps.

lib/spring/application_manager.rb

@@ -126,7 +126,8 @@ def start_wait_thread(pid, child)
         # as if it does we're no longer interested in the child
         loop do
           IO.select([child])
-          break if child.recv(1, Socket::MSG_PEEK).empty?
+          peek = child.recv(1, Socket::MSG_PEEK)
+          break if peek.nil? || peek.empty?
           sleep 0.01
         end
 

test/support/acceptance_test.rb

@@ -189,7 +189,7 @@ def self.omg
         app.insert_into_test "Foo.omg"
 
         app.await_reload
-        assert_failure app.spring_test_command, stdout: "RuntimeError: omg"
+        assert_failure app.spring_test_command, stdout: "RuntimeError: omg", log: /child \d+ shutdown/
       end
 
       test "app gets reloaded even with a ton of boot output" do