let's warn with heredocs

The current style for warning messages without newlines uses
concatenation of string literals with manual trailing spaces
where needed.

Heredocs have better readability, and with `squish` we can still
produce a single line.

This is a similar use case to the one that motivated defining
`strip_heredoc`, heredocs are super clean.

1 files changed, 8 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 57affce4f7..1b84fdf5f2 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/string/filters'
+
 module ActiveRecord
   # = Active Record Has Many Through Association
   module Associations
@@ -63,11 +65,12 @@ module ActiveRecord
 
         save_through_record(record)
         if has_cached_counter? && !through_reflection_updates_counter_cache?
-          ActiveSupport::Deprecation.warn \
-            "Automatic updating of counter caches on through associations has been " \
-            "deprecated, and will be removed in Rails 5.0. Instead, please set the " \
-            "appropriate counter_cache options on the has_many and belongs_to for " \
-            "your associations to #{through_reflection.name}."
+          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+            Automatic updating of counter caches on through associations has been
+            deprecated, and will be removed in Rails 5.0. Instead, please set the
+            appropriate counter_cache options on the has_many and belongs_to for
+            your associations to #{through_reflection.name}.
+          MSG
 
           update_counter_in_database(1)
         end