Accept unix:// URLs for the Redis backend

ruby/lib/ci/queue.rb

@@ -81,7 +81,13 @@ def from_uri(url, config)
         Static
       when 'file', nil
         File
-      when 'redis', 'rediss'
+      when 'redis', 'rediss', 'unix'
+        # `unix://` URLs are forwarded to the Redis backend as-is;
+        # redis-client's URL parser accepts the unix:// scheme natively
+        # and treats the path as the socket path. This lets workloads
+        # that already run an in-process Redis on a unix socket (Nix
+        # build sandboxes, hermetic test harnesses, etc.) point ci-queue
+        # at it without exposing a TCP port.
         require 'ci/queue/redis'
         Redis
       else

ruby/test/ci/queue/redis_test.rb

@@ -624,6 +624,11 @@ def test_initialise_from_rediss_uri
     assert_instance_of CI::Queue::Redis::Worker, queue
   end
 
+  def test_initialise_from_unix_uri
+    queue = CI::Queue.from_uri('unix:///tmp/redis.sock', config)
+    assert_instance_of CI::Queue::Redis::Worker, queue
+  end
+
   def test_first_reserve_at_is_set_on_first_reserve
     queue = worker(1)
     assert_nil queue.first_reserve_at