Add connection pool to connection timeout errors

Along the same lines as rails#48295,
in multi-database applications it's helpful to have access to the pool
when debugging these timeouts. For example, we might send the connection
class and role along to an exception tracking system.

ConnectionTimeout was already set up to take a connection_pool, so this
commit passes it along as needed where we raise the error.

Author: composerinteralia

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -614,7 +614,7 @@ def checkout_for_exclusive_access(checkout_timeout)
 
           msg << " (#{thread_report.join(', ')})" if thread_report.any?
 
-          raise ExclusiveConnectionTimeoutError, msg
+          raise ExclusiveConnectionTimeoutError.new(msg, connection_pool: self)
         end
 
         def with_new_connections_blocked
@@ -670,6 +670,8 @@ def acquire_connection(checkout_timeout)
             reap
             @available.poll(checkout_timeout)
           end
+        rescue ConnectionTimeoutError => ex
+          raise ex.set_pool(self)
         end
 
         #--

activerecord/test/cases/connection_pool_test.rb

@@ -110,9 +110,10 @@ def test_full_pool_exception
         @pool.checkout_timeout = 0.001 # no need to delay test suite by waiting the whole full default timeout
         @pool.size.times { assert @pool.checkout }
 
-        assert_raises(ConnectionTimeoutError) do
+        error = assert_raises(ConnectionTimeoutError) do
           @pool.checkout
         end
+        assert_equal @pool, error.connection_pool
       end
 
       def test_full_pool_blocks
@@ -615,9 +616,10 @@ def test_non_bang_disconnect_and_clear_reloadable_connections_throw_exception_if
         @pool.checkout_timeout = 0.001 # no need to delay test suite by waiting the whole full default timeout
         [:disconnect, :clear_reloadable_connections].each do |group_action_method|
           @pool.with_connection do |connection|
-            assert_raises(ExclusiveConnectionTimeoutError) do
+            error = assert_raises(ExclusiveConnectionTimeoutError) do
               new_thread { @pool.public_send(group_action_method) }.join
             end
+            assert_equal @pool, error.connection_pool
           end
         end
       ensure