`where.not` with polymorphic association is partly fixed incidentally at
213796fb (refer #33493, #26207, #17010, #16983, #14161), and I've added
test case e9ba12f7 to avoid lose that fix accidentally in the future.

In Rails 5.2, `where.not(polymorphic: object)` works as expected as
NAND, but `where.not(polymorphic_type: object.class.polymorphic_name,
polymorphic_id: object.id)` still unexpectedly works as NOR.

To will make `where.not` working desiredly as NAND in Rails 6.1, this
deprecates `where.not` working as NOR. If people want to continue NOR
conditions, we'd encourage to them to `where.not` each conditions
manually.

```ruby
all = [treasures(:diamond), treasures(:sapphire), cars(:honda), treasures(:sapphire)]
assert_equal all, PriceEstimate.all.map(&:estimate_of)
```

In Rails 6.0:

```ruby
sapphire = treasures(:sapphire)

nor = all.reject { |e|
  e.estimate_of_type == sapphire.class.polymorphic_name
}.reject { |e|
  e.estimate_of_id == sapphire.id
}
assert_equal [cars(:honda)], nor

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nor, without_sapphire.map(&:estimate_of)
```

In Rails 6.1:

```ruby
sapphire = treasures(:sapphire)

nand = all - [sapphire]
assert_equal [treasures(:diamond), cars(:honda)], nand

without_sapphire = PriceEstimate.where.not(
  estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id: sapphire.id
)
assert_equal nand, without_sapphire.map(&:estimate_of)
```

Resolves #31209.

Cache versioning enables the same cache key to be reused when the object
being cached changes by moving the volatile part of the cache key out of
the cache key and into a version that is embedded in the cache entry.

This is already occurring when the object being cached is an
`ActiveRecord::Base`, but when caching an `ActiveRecord::Relation`
we are currently still putting the volatile information (max updated at
and count) as part of the cache key.

This PR moves the volatile part of the relations `cache_key` into the
`cache_version` to support recycling cache keys for
`ActiveRecord::Relation`s.

Currently the rollback only restores primary key value, `new_record?`,
`destroyed?`, and `frozen?`. Since the `save` clears current dirty
attribute states, retrying save after rollback will causes no change
saved if partial writes is enabled (by default).

This makes `remember_transaction_record_state` remembers original values
then restores dirty attribute states after rollback.

Fixes #15018.
Fixes #30167.
Fixes #33868.
Fixes #33443.
Closes #33444.
Closes #34504.

[ci skip]

We can revert migrations using `change_column_comment` or
`change_table_comment` at current master.
However, results are not what we expect: comments are remained in new
status.
This change tells previous comment to these methods in a way like
`change_column_default`.

Regardless of a record isn't saved (e.g. validation is failed),
`after_commit` / `after_rollback` callbacks are invoked for now.

To fix the issue, this adds a record to the current transaction only
when a record is actually saved.

Fixes #29747.
Closes #29833.

When I've added new `:size` option in #35071, I've found that invalid
`:limit` and `:precision` raises `ActiveRecordError` unlike other
invalid options.

I think that is hard to distinguish argument errors and statement
invalid errors since the `StatementInvalid` is a subclass of the
`ActiveRecordError`.

https://github.com/rails/rails/blob/c9e4c848eeeb8999b778fa1ae52185ca5537fffe/activerecord/lib/active_record/errors.rb#L103

```ruby
begin
  # execute any migration
rescue ActiveRecord::StatementInvalid
  # statement invalid
rescue ActiveRecord::ActiveRecordError, ArgumentError
  # `ActiveRecordError` except `StatementInvalid` is maybe an argument error
end
```

I'd say this is the inconsistency worth fixing.

Before:

```ruby
add_column :items, :attr1, :binary,   size: 10      # => ArgumentError
add_column :items, :attr2, :decimal,  scale: 10     # => ArgumentError
add_column :items, :attr3, :integer,  limit: 10     # => ActiveRecordError
add_column :items, :attr4, :datetime, precision: 10 # => ActiveRecordError
```

After:

```ruby
add_column :items, :attr1, :binary,   size: 10      # => ArgumentError
add_column :items, :attr2, :decimal,  scale: 10     # => ArgumentError
add_column :items, :attr3, :integer,  limit: 10     # => ArgumentError
add_column :items, :attr4, :datetime, precision: 10 # => ArgumentError
```

Follow-up of 5c71000d, #29834, and #30271.

Currently, preloading and eager loading are not to be affected by
scoping, with the exception of `unscoped`.

But non eager loaded association access is still affected by scoping.

Although this is a breaking change, the association loading will work
consistently whether preloaded / eager loaded or not.

Before:

```ruby
Post.where("1=0").scoping do
  Comment.find(1).post                   # => nil
  Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
  Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
end
```

After:

```ruby
Post.where("1=0").scoping do
  Comment.find(1).post                   # => #<Post id: 1, ...>
  Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
  Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>
end
```

Fixes #34638.
Fixes #35398.

* s/Postgres/PostgreSQL/
* s/MYSQL/MySQL/, s/Mysql/MySQL/
* s/Sqlite/SQLite/

Replaced all newly added them after 6089b314.

Add `after_save_commit` callback as shortcut for `after_commit :hook, on: [ :create, :update ]`. (#35804)

* use backticks instead of `+`
* and more (e.g. missed replacing `Array#excluding` and
`Enumerable#excluding` in b89a3e7e)

When adding a child record via a has_many :through association,
build_through_record would previously build the join record, and then
assign the child record and source_type option to it.  Because the
before_add and after_add callbacks are called as part of build, however,
this caused the callbacks to receive incomplete records, specifically
without the other end of the has_many :through association.  Collecting
all attributes before building the join record ensures the callbacks
receive the fully constructed record.

* Add `ActiveRecord::Relation#extract_associated` for extracting associated records from a relation

This patch has two main portions:

1. Add SQL comment support to Arel via Arel::Nodes::Comment.
2. Implement a Relation#annotate method on top of that.

== Adding SQL comment support

Adds a new Arel::Nodes::Comment node that represents an optional SQL
comment and teachers the relevant visitors how to handle it.

Comment nodes may be added to the basic CRUD statement nodes and set
through any of the four (Select|Insert|Update|Delete)Manager objects.

For example:

    manager = Arel::UpdateManager.new
    manager.table table
    manager.comment("annotation")
    manager.to_sql # UPDATE "users" /* annotation */

This new node type will be used by ActiveRecord::Relation to enable
query annotation via SQL comments.

== Implementing the Relation#annotate method

Implements `ActiveRecord::Relation#annotate`, which accepts a comment
string that will be appeneded to any queries generated by the relation.

Some examples:

    relation = Post.where(id: 123).annotate("metadata string")
    relation.first
    # SELECT "posts".* FROM "posts" WHERE "posts"."id" = 123
    # LIMIT 1 /* metadata string */

    class Tag < ActiveRecord::Base
      scope :foo_annotated, -> { annotate("foo") }
    end
    Tag.foo_annotated.annotate("bar").first
    # SELECT "tags".* FROM "tags" LIMIT 1 /* foo */ /* bar */

Also wires up the plumbing so this works with `#update_all` and
`#delete_all` as well.

This feature is useful for instrumentation and general analysis of
queries generated at runtime.

We as Arm Treasure Data are using Optimizer Hints with a monkey patch
(https://gist.github.com/kamipo/4c8539f0ce4acf85075cf5a6b0d9712e),
especially in order to use `MAX_EXECUTION_TIME` (refer #31129).

Example:

```ruby
class Job < ApplicationRecord
  default_scope { optimizer_hints("MAX_EXECUTION_TIME(50000) NO_INDEX_MERGE(jobs)") }
end
```

Optimizer Hints is supported not only for MySQL but also for most
databases (PostgreSQL on RDS, Oracle, SQL Server, etc), it is really
helpful to turn heavy queries for large scale applications.

* Update RAILS_VERSION
* Bundle
* rake update_versions
* rake changelog:header

change the line to check an attribute has user-defined type

ref: https://github.com/rails/rails/pull/35320#discussion_r257924552

check query attribute method is working when given value does not respond to to_i method

Adds a method to ActiveRecord allowing records to be inserted in bulk without instantiating ActiveRecord models. This method supports options for handling uniqueness violations by skipping duplicate records or overwriting them in an UPSERT operation.

ActiveRecord already supports bulk-update and bulk-destroy actions that execute SQL UPDATE and DELETE commands directly. It also supports bulk-read actions through `pluck`. It makes sense for it also to support bulk-creation.

* Add `ActiveRecord::Base.connection.truncate` for SQLite3 adapter.

SQLite doesn't support `TRUNCATE TABLE`, but SQLite3 adapter can support
`ActiveRecord::Base.connection.truncate` by using `DELETE FROM`.

`DELETE` without `WHERE` uses "The Truncate Optimization",
see https://www.sqlite.org/lang_delete.html.

* Add `rails db:seed:replant` that truncates database tables and loads the seeds

Closes #34765

In MySQL, the default collation is case insensitive. Since the
uniqueness validator enforces case sensitive comparison by default, it
frequently causes mismatched collation issues (performance, weird
behavior, etc) to MySQL users.

https://grosser.it/2009/12/11/validates_uniqness_of-mysql-slow/
https://github.com/rails/rails/issues/1399
https://github.com/rails/rails/pull/13465
https://github.com/gitlabhq/gitlabhq/commit/c1dddf8c7d947691729f6d64a8ea768b5c915855
https://github.com/huginn/huginn/pull/1330#discussion_r55152573

I'd like to deprecate the implicit default enforcing since I frequently
experienced the problems in code reviews.

Note that this change has no effect to sqlite3, postgresql, and
oracle-enhanced adapters which are implemented as case sensitive by
default, only affect to mysql2 adapter (I can take a work if sqlserver
adapter will support Rails 6.0).

Fixes https://github.com/rails/rails/pull/33611#discussion_r261549790
Related to https://3.basecamp.com/3076981/buckets/24956/chats/12416418@1631552581

[ci skip]

Add negative scopes for all enum values

When using `select` with `'DISTINCT( ... )'` if you use method `size` on a non loaded relation it overrides the column selected by passing `:all` so it returns different value than count.

This fixes #35214

Related cbcdecd2, 2a56b2d9.

This is a regression caused by cbcdecd2.

If query caching is enabled, prepared statement handles are never
re-used, since we missed that a query is preprocessed when query caching
is enabled, but doesn't keep the `preparable` flag.

We should care about that case.

Incrementing the lock version invalidates any other process's optimistic
lock, which is the desired outcome: the record no longer looks the same
as it did when they loaded it.

This is a follow-up of #35310.

Currently `Topic.find_by(id: "not-a-number")` matches to a `id = 0`
record. That is considered as silently leaking information.

If non numeric string is given to find by an integer column, it should
not be matched to any record.

Related #12793.

That is considered as silently leaking information.
If type casting doesn't return any actual value, it should not be
matched to any record.

Fixes #33624.
Closes #33946.

[ci skip]