11 files changed, 17 insertions, 12 deletions
diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 0ca18d98a1..d7435fa8df 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -12,9 +12,6 @@ module ActionDispatch
       end
 
       # The MIME type of the HTTP request, such as Mime[:xml].
-      #
-      # For backward compatibility, the post \format is extracted from the
-      # X-Post-Data-Format HTTP header if present.
       def content_mime_type
         fetch_header("action_dispatch.request.content_type") do |k|
           v = if get_header("CONTENT_TYPE") =~ /^([^,\;]*)/
diff --git a/actionpack/lib/action_dispatch/system_testing/server.rb b/actionpack/lib/action_dispatch/system_testing/server.rb
index 32aa6a4dc4..8f1b6725b1 100644
--- a/actionpack/lib/action_dispatch/system_testing/server.rb
+++ b/actionpack/lib/action_dispatch/system_testing/server.rb
@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require "rack/handler/puma"
-
 module ActionDispatch
   module SystemTesting
     class Server # :nodoc:
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 3e1b467633..4aa7ecfc7e 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -347,10 +347,6 @@
 
     *Ryuta Kamizono*
 
-*   Quote database name in `db:create` grant statement (when database user does not have access to create the database).
-
-    *Rune Philosof*
-
 *   Raise error `UnknownMigrationVersionError` on the movement of migrations
     when the current migration does not exist.
 
diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
index 07bd0a273b..14881cfe17 100644
--- a/activerecord/lib/active_record/associations/alias_tracker.rb
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -33,7 +33,7 @@ module ActiveRecord
           elsif join.respond_to? :left
             join.left.name == name ? 1 : 0
           elsif join.is_a?(Hash)
-            join[name]
+            join.fetch(name, 0)
           else
             # this branch is reached by two tests:
             #
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 8877f762b2..c18214a842 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -1002,7 +1002,7 @@ module ActiveRecord
     end
 
     class PolymorphicReflection < AbstractReflection # :nodoc:
-      delegate :klass, :scope, :plural_name, :type, :get_join_keys, to: :@reflection
+      delegate :klass, :scope, :plural_name, :type, :get_join_keys, :scope_for, to: :@reflection
 
       def initialize(reflection, previous_reflection)
         @reflection = reflection
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index c6a4ac356f..046020e310 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -1250,7 +1250,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     TenantMembership.current_member = nil
   end
 
-  def test_has_many_trough_with_scope_that_has_joined_same_table_with_parent_relation
+  def test_has_many_through_with_scope_that_has_joined_same_table_with_parent_relation
     assert_equal authors(:david), Author.joins(:comments_for_first_author).take
   end
 
@@ -1258,6 +1258,10 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal [comments(:eager_other_comment1)], authors(:mary).unordered_comments
   end
 
+  def test_has_many_through_with_scope_should_accept_string_and_hash_join
+    assert_equal authors(:david), Author.joins({ comments_for_first_author: :post }, "inner join posts posts_alias on authors.id = posts_alias.author_id").eager_load(:categories).take
+  end
+
   def test_has_many_through_with_scope_should_respect_table_alias
     family = Family.create!
     users = 3.times.map { User.create! }
diff --git a/activerecord/test/cases/associations/nested_through_associations_test.rb b/activerecord/test/cases/associations/nested_through_associations_test.rb
index 3e37e512ca..ab3bf5eb8d 100644
--- a/activerecord/test/cases/associations/nested_through_associations_test.rb
+++ b/activerecord/test/cases/associations/nested_through_associations_test.rb
@@ -425,6 +425,11 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     assert authors.empty?
   end
 
+  def test_nested_has_many_through_with_scope_on_polymorphic_reflection
+    authors = Author.joins(:ordered_posts).where("posts.id" => posts(:misc_by_bob).id)
+    assert_equal [authors(:mary), authors(:bob)], authors.distinct.sort_by(&:id)
+  end
+
   def test_has_many_through_with_foreign_key_option_on_through_reflection
     assert_equal [posts(:welcome), posts(:authorless)], people(:david).agents_posts.order("posts.id")
     assert_equal [authors(:david)], references(:david_unicyclist).agents_posts_authors
diff --git a/activerecord/test/models/author.rb b/activerecord/test/models/author.rb
index e9eba9be2e..cb8686f315 100644
--- a/activerecord/test/models/author.rb
+++ b/activerecord/test/models/author.rb
@@ -101,10 +101,12 @@ class Author < ActiveRecord::Base
   has_many :taggings,        through: :posts, source: :taggings
   has_many :taggings_2,      through: :posts, source: :tagging
   has_many :tags,            through: :posts
+  has_many :ordered_tags,    through: :posts
   has_many :post_categories, through: :posts, source: :categories
   has_many :tagging_tags,    through: :taggings, source: :tag
 
   has_many :similar_posts, -> { distinct }, through: :tags, source: :tagged_posts
+  has_many :ordered_posts, -> { distinct }, through: :ordered_tags, source: :tagged_posts
   has_many :distinct_tags, -> { select("DISTINCT tags.*").order("tags.name") }, through: :posts, source: :tags
 
   has_many :tags_with_primary_key, through: :posts
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 935a11e811..7f064bf3dd 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -115,6 +115,7 @@ class Post < ActiveRecord::Base
   has_many :misc_tags, -> { where tags: { name: "Misc" } }, through: :taggings, source: :tag
   has_many :funky_tags, through: :taggings, source: :tag
   has_many :super_tags, through: :taggings
+  has_many :ordered_tags, through: :taggings
   has_many :tags_with_primary_key, through: :taggings, source: :tag_with_primary_key
   has_one :tagging, as: :taggable
 
diff --git a/activerecord/test/models/tag.rb b/activerecord/test/models/tag.rb
index 4495ac4a09..bc13c3a42d 100644
--- a/activerecord/test/models/tag.rb
+++ b/activerecord/test/models/tag.rb
@@ -12,4 +12,5 @@ class OrderedTag < Tag
   self.table_name = "tags"
 
   has_many :taggings, -> { order("taggings.id DESC") }, foreign_key: "tag_id"
+  has_many :tagged_posts, through: :taggings, source: "taggable", source_type: "Post"
 end
diff --git a/activerecord/test/models/tagging.rb b/activerecord/test/models/tagging.rb
index fc0af026c5..861fde633f 100644
--- a/activerecord/test/models/tagging.rb
+++ b/activerecord/test/models/tagging.rb
@@ -8,6 +8,7 @@ class Tagging < ActiveRecord::Base
   belongs_to :tag, -> { includes(:tagging) }
   belongs_to :super_tag,   class_name: "Tag", foreign_key: "super_tag_id"
   belongs_to :invalid_tag, class_name: "Tag", foreign_key: "tag_id"
+  belongs_to :ordered_tag, class_name: "OrderedTag", foreign_key: "tag_id"
   belongs_to :blue_tag, -> { where tags: { name: "Blue" } }, class_name: "Tag", foreign_key: :tag_id
   belongs_to :tag_with_primary_key, class_name: "Tag", foreign_key: :tag_id, primary_key: :custom_primary_key
   belongs_to :taggable, polymorphic: true, counter_cache: :tags_count