Fix merging left_joins to maintain its own `join_type` context

This fixes a regression for #35864.

Usually, stashed joins (mainly eager loading) are performed as LEFT
JOINs.
But the case of merging joins/left_joins of different class, that
(stashed) joins are performed as the same `join_type` as the parent
context for now.
Since #35864, both (joins/left_joins) stashed joins might be contained
in `joins_values`, so each stashed joins should maintain its own
`join_type` context.

Fixes #36103.

1 files changed, 6 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index 6bb77b355c..84fe424ef0 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -123,7 +123,9 @@ module ActiveRecord
               end
             end
 
-            join_dependency = other.construct_join_dependency(associations)
+            join_dependency = other.construct_join_dependency(
+              associations, Arel::Nodes::InnerJoin
+            )
             relation.joins!(join_dependency, *others)
           end
         end
@@ -135,7 +137,9 @@ module ActiveRecord
             relation.left_outer_joins!(*other.left_outer_joins_values)
           else
             associations = other.left_outer_joins_values
-            join_dependency = other.construct_join_dependency(associations)
+            join_dependency = other.construct_join_dependency(
+              associations, Arel::Nodes::OuterJoin
+            )
             relation.joins!(join_dependency)
           end
         end