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, 13 insertions, 4 deletions

diff --git a/actionmailer/lib/action_mailer/message_delivery.rb b/actionmailer/lib/action_mailer/message_delivery.rb
index c18e914f37..e058b3b15d 100644
--- a/actionmailer/lib/action_mailer/message_delivery.rb
+++ b/actionmailer/lib/action_mailer/message_delivery.rb
@@ -1,4 +1,5 @@
 require 'delegate'
+require 'active_support/core_ext/string/filters'
 
 module ActionMailer
 
@@ -85,14 +86,22 @@ module ActionMailer
     end
 
     def deliver! #:nodoc:
-      ActiveSupport::Deprecation.warn "#deliver! is deprecated and will be removed in Rails 5. " \
-        "Use #deliver_now! to deliver immediately or #deliver_later! to deliver through Active Job."
+      ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        #deliver! is deprecated and will be removed in Rails 5. Use
+        #deliver_now! to deliver immediately or #deliver_later! to
+        deliver through Active Job.
+      MSG
+
       deliver_now!
     end
 
     def deliver #:nodoc:
-      ActiveSupport::Deprecation.warn "#deliver is deprecated and will be removed in Rails 5. " \
-        "Use #deliver_now to deliver immediately or #deliver_later to deliver through Active Job."
+      ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        #deliver is deprecated and will be removed in Rails 5. Use
+        #deliver_now to deliver immediately or #deliver_later to
+        deliver through Active Job.
+      MSG
+
       deliver_now
     end