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.

3 files changed, 22 insertions, 9 deletions

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index c95ec2522b..ddb392a6d4 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -1,4 +1,5 @@
 require 'active_support/deprecation'
+require 'active_support/core_ext/string/filters'
 
 module ActiveRecord
   module FinderMethods
@@ -284,8 +285,10 @@ module ActiveRecord
     def exists?(conditions = :none)
       if Base === conditions
         conditions = conditions.id
-        ActiveSupport::Deprecation.warn "You are passing an instance of ActiveRecord::Base to `exists?`." \
-          "Please pass the id of the object by calling `.id`"
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          You are passing an instance of ActiveRecord::Base to `exists?`.
+          Please pass the id of the object by calling `.id`
+        MSG
       end
 
       return false if !conditions
@@ -435,8 +438,10 @@ module ActiveRecord
     def find_one(id)
       if ActiveRecord::Base === id
         id = id.id
-        ActiveSupport::Deprecation.warn "You are passing an instance of ActiveRecord::Base to `find`." \
-          "Please pass the id of the object by calling `.id`"
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          You are passing an instance of ActiveRecord::Base to `find`.
+          Please pass the id of the object by calling `.id`
+        MSG
       end
 
       column = columns_hash[primary_key]
diff --git a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
index b8d9240bf8..b6a9b4f63a 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/string/filters'
+
 module ActiveRecord
   class PredicateBuilder
     class ArrayHandler # :nodoc:
@@ -6,9 +8,12 @@ module ActiveRecord
         nils, values = values.partition(&:nil?)
 
         if values.any? { |val| val.is_a?(Array) }
-          ActiveSupport::Deprecation.warn "Passing a nested array to Active Record " \
-            "finder methods is deprecated and will be removed. Flatten your array " \
-            "before using it for 'IN' conditions."
+          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+            Passing a nested array to Active Record finder methods is
+            deprecated and will be removed. Flatten your array before using
+            it for 'IN' conditions.
+          MSG
+
           values = values.flatten
         end
 
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index e4bebf78e8..2c3cfb7631 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/array/wrap'
+require 'active_support/core_ext/string/filters'
 require 'active_model/forbidden_attributes_protection'
 
 module ActiveRecord
@@ -94,8 +95,10 @@ module ActiveRecord
     def check_cached_relation # :nodoc:
       if defined?(@arel) && @arel
         @arel = nil
-        ActiveSupport::Deprecation.warn "Modifying already cached Relation. The " \
-          "cache will be reset. Use a cloned Relation to prevent this warning."
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          Modifying already cached Relation. The cache will be reset. Use a
+          cloned Relation to prevent this warning.
+        MSG
       end
     end