Set the join type on construction

We always set the join type immediately after construction, just make it
part of the constructor and we can skip that step

activerecord/lib/active_record/associations/join_dependency.rb

@@ -137,8 +137,7 @@ def build(associations, parent = join_parts.last, join_type = Arel::InnerJoin)
           raise ConfigurationError, "Association named '#{ associations }' was not found on #{ parent.base_klass.name }; perhaps you misspelled it?"
           unless join_association = find_join_association(reflection, parent)
             @reflections << reflection
-            join_association = build_join_association(reflection, parent)
-            join_association.join_type = join_type
+            join_association = build_join_association(reflection, parent, join_type)
             @join_parts << join_association
             cache_joined_association(join_association)
           end
@@ -173,14 +172,14 @@ def remove_uniq_by_reflection(reflection, records)
         end
       end
 
-      def build_join_association(reflection, parent)
+      def build_join_association(reflection, parent, join_type)
         reflection.check_validity!
 
         if reflection.options[:polymorphic]
           raise EagerLoadPolymorphicError.new(reflection)
         end
 
-        JoinAssociation.new(reflection, self, parent)
+        JoinAssociation.new(reflection, self, parent, join_type)
       end
 
       def construct(parent, associations, join_parts, row)

activerecord/lib/active_record/associations/join_dependency/join_association.rb

@@ -29,13 +29,13 @@ class JoinAssociation < JoinPart # :nodoc:
         delegate :options, :through_reflection, :source_reflection, :chain, :to => :reflection
         delegate :alias_tracker, :to => :join_dependency
 
-        def initialize(reflection, join_dependency, parent)
+        def initialize(reflection, join_dependency, parent, join_type)
           super(reflection.klass)
 
           @reflection      = reflection
           @join_dependency = join_dependency
           @parent          = parent
-          @join_type       = Arel::InnerJoin
+          @join_type       = join_type
           @aliased_prefix  = "t#{ join_dependency.join_parts.size }"
           @tables          = construct_tables.reverse
         end