Dangerous name conflicts includes instance or class method conflicts
with methods defined within `ActiveRecord::Base` but not its ancestors,
as well as conflicts with methods generated by other enums on the same
class.

Fixes #13389.

Similar to dangerous attribute methods, a scope name conflict is
dangerous if it conflicts with an existing class method defined within
`ActiveRecord::Base` but not its ancestors.

See also #13389.

*Godfrey Chan*, *Philippe Creux*

Before:

  >> ActiveRecord::Base.respond_to?(:find_by_something)
  NoMethodError: undefined method `abstract_class?' for Object:Class

After:

  >> ActiveRecord::Base.respond_to?(:find_by_something)
  => false

As per the documentation at lock!, if the :lock option is a string it should use the given SQL to generate the lock statement.

With this we can write `Model#select(:aliased)`, `Model#order(:aliased)`,
`Model#reoder(aliased: :desc)`, etc.

Supplementary work to 54122067.

Add docs about behaviour of replacing a has_one associate object, that the previous one is deleted even if the new one
 doesn't get persisted to database.

 Fixes #13197 . [ci skip]

Hopefully make it easier to debug errors. e.g

Before:

    RuntimeError:
       unscope(where: "deleted_at") failed: unscoping String is unimplemented.

After:

    RuntimeError:
       unscope(where: "deleted_at") failed: unscoping String "'t'='t'" is unimplemented.

Move serialization dirty into serialization.rb

Need to define #reset on CollectionProxy.

This commit fixes two regressions introduced in cafe31a0 where
newly created finder methods #second, #third, #forth, and #fifth
caused a NoMethodError error on reload associations and where we
were pulling the wrong element out of cached associations.

Examples:

  some_book.authors.reload.second

  # Before
  # => NoMethodError: undefined method 'first' for nil:NilClass

  # After
  # => #<Author id: 2, name: "Sally Second", ...>

  some_book.first.authors.first
  some_book.first.authors.second

  # Before
  # => #<Author id: 1, name: "Freddy First", ...>
  # => #<Author id: 1, name: "Freddy First", ...>

  # After
  # => #<Author id: 1, name: "Freddy First", ...>
  # => #<Author id: 2, name: "Sally Second", ...>

Fixes #13783.

This will make simpler to compare if the values changed in the
save_changed_attribute method.

Since Rails 4.0, we add an ORDER BY in the `first` method to ensure consistent
results among different database engines. But for singular associations this
behavior is not needed since we will have one record to return. As this
ORDER BY option can lead some performance issues we are removing it for singular
associations accessors.

Fixes #12623.

This fixes a bug where `select(:id)` combined with `joins()` raised:

```
ActiveRecord::StatementInvalid: SQLite3::SQLException: ambiguous column name: id:
SELECT  id, authors.author_address_id
FROM "posts"
INNER JOIN "authors"
ON "authors"."id" = "posts"."author_id"
ORDER BY posts.id LIMIT 3
```

The `select_values` are still String and Symbols because other parts (mainly calculations.rb)
rely on that fact.

/cc @tenderlove

To make this possible we have to override the save_changed_attribute
hook.

This will make easier to hook on this feature to customize the behavior

Before this patch find_in_batches raises this error only on second iteration. So you will know about the problem only when you get the batch size threshold.

With the introduction of `#second` method and friends, we added an
offsets hash which replaced the @first variable, so removing it from the
reset method to avoid creating an unused variable now.

Introduced in bc625080.

This variable is internal and should not be exposed to end users

This commit bring the famous ordinal Array instance methods defined
in ActiveSupport into ActiveRecord as fully-fledged finders.

These finders ensure a default ascending order of the table's primary
key, and utilize the OFFSET SQL verb to locate the user's desired
record. If an offset is defined in the query, calling #second adds
to the offset to get the actual desired record.

Fixes #13743.

This fixes a regression (#13744) that was caused by 67d8bb96.

In 67d8bb96, we introduced lazy rollback for records, such that the
record's internal states and attributes are not restored immediately
after a transaction rollback, but deferred until they are first
accessed.

This optimization is only performed when the model does not have any
transactional callbacks (e.g. `after_commit` and `after_create`).

Unfortunately, the models used to test the affected codepaths all
comes with some sort of transactional callbacks. Therefore this
codepath remains largely untested until now and as a result there are
a few issues in the implementation that remains hidden until now.

First, the `sync_with_transaction_state` (or more accurately,
`update_attributes_from_transaction_state`) would perform the
synchronization prematurely before a transaction is finalized (i.e.
comitted or rolled back). As a result, when the actuall rollback
happens, the record will incorrectly assumes that its internal states
match the transaction state, and neglect to perform the restore.

Second, `update_attributes_from_transaction_state` calls `committed!`
in some cases. This in turns checks for the `destroyed?` state which
also requires synchronization with the transaction stae, which causes
an infnite recurrsion.

This fix works by deferring the synchronization until the transaction
has been finalized (addressing the first point), and also unrolled
the `committed!` and `rolledback!` logic in-place (addressing the
second point).

It should be noted that the primary purpose of the `committed!` and
`rolledback!` methods are to trigger the relevant transactional
callbacks. Since this code path is only entered when there are no
transactional callbacks on the model, this shouldn't be necessary. By
unrolling the method calls, the intention here (to restore the states
when necessary) becomes more clear.

This has been added 9 years ago in
a677da20, and removed 6 years ago in
38f8252e.

rather than allocating a new Relation, just make the AST directly

The `subclass_from_attrs` method is called even if the column specified by
the `inheritance_column` setting doesn't exist. This prevents setting associations
via the attributes hash if the association name clashes with the value of the setting,
typically `:type`. This worked previously in Rails 3.2.

Example:

    class Conversation < ActiveRecord::Base
      enum status: [ :active, :archived ]
    end

Before:

    Conversation::STATUS # => { "active" => 0, "archived" => 1 }

After:

    Conversation.statuses # => { "active" => 0, "archived" => 1 }