Follow up #32146.

Remove index:true option from belongs to as defaults to true.

[ci skip]

Update guide for the counter variable when rendering with the `as:` option

`init_with` and `init_from_db` are almost the same code except decode
`coder`.

And also, named `init_from_db` is a little misreading, a raw values hash
from the database is already converted to an attributes object by
`attributes_builder.build_from_database`, so passed `attributes` in that
method is just an attributes object.

I renamed that method to `init_with_attributes` since the method is
shared with `init_with` to initialize an empty model object.

[ci skip]

Consistently extract checking version for all adapters

Use \X meta character directly to get grapheme clusters.

Thanks to @mtsmfm for the tip:
https://github.com/rails/rails/pull/34123#issuecomment-429028878

r? @jeremy

I don't prefer to extract it for one adapter even though all adapters
also does.

Related to #34227.

Fix mapping of content [ci skip]

Refactored abstract MySQL adapter to support lazy version check.

Clarify docs of `ActiveJob::TestHelper` [ci skip]

Will allow sub classes to override the protected
`#check_version` method hook if desired.

For example, this will be most helpful in sub classes that wish
to support lazy initialization because the version check can
be postponed until the connection is ready to be initialized.

Add regression test against has_and_belong_to_many memoized singular_ids

Extend doc for ActiveSupport::Cache#fetch_multi

Starting in Rails 5.0.0 and still present in Rails 5.2.1, `singular_ids`
got memoized and didn't reload after more items were added to the
relation.

Although 19c80718 happens to fix the issue, it only adds tests for
`has_many` relations while this bug only affected
`has_and_belongs_to_many` relations.

This commit adds a regression test to ensure it never happens again with
`habtm` relations.

Ensures #34179 never gets reproduced.

Issue #29200 scaffold an object with a reference displays an object memory address to user

Fix Collection cache key with limit and custom select

Change query to use alias name for timestamp_column to avoid ambiguity problems when using timestamp from subquery.

I found a few sentences that should be updated as well.
See https://github.com/rails/rails/pull/33571#discussion_r209435886

Follow up #33571

In favor of String#is_utf8?.

I think this method was made for internal use only, and its usage was removed here: https://github.com/rails/rails/pull/8261/files#diff-ce956ebe93786930e40f18db1da5fd46L39.

Update snippet to rails 5 syntax

[ci skip]

* Fix `ActionController::Parameters#each_value`

`each_value` should yield with "value" of the params instead of "value" as an array.
Related to #33979

* Add changelog entry about `ActionController::Parameters#each_value`.

Follow up #33979

Fix issue where duration where always rounded up to a second:

`developers.name desc` was added at d59f3a78, but any test case isn't
failed even if the `developers.name desc` is removed since all tested
developers are consistently ordered on both `name` and `id`.

I changed one developers creation ordering to ensure to test that
`project.developers` is ordered by `developers.name desc`.

Fix tests on Mail 2.7.1

Resolve Issue#29200

When scaffolding a model that references another model the
generated show and index html pages display the object directly
on the page. Basically, it just shows a memory address. That is
not very helpful. In this commit we show the object's id rather
than the memory address.

This updates the scaffold templates and the json builder files.

Up to `2.7.0`, encoding was chosen using `Mail::Encodings::TransferEncoding.negotiate`,
and base64 encoding was used.
In `2.7.1`, when `transfer_encoding` is not specified, the encoding
of the message is respected.
Related to: https://github.com/mikel/mail/commit/dead487e02f592d9058fd07deedcde39b569d18d

However, what chosen for transfer encoding is not essential in these tests.
To test more accurately, confirm that the decoded body instead.

- Adding a Float as a duration to a datetime would result in the Float
  being rounded. Doing something like would have no effect because the
  0.45 seconds would be rounded to 0 second.

  ```ruby
    time = DateTime.parse("2018-1-1")
    time += 0.45.seconds
  ```

  This behavior was intentionally added a very long time ago, the
  reason was because Ruby 1.8 was using `Integer#gcd` in the
  constructor of Rational which didn't accept a float value.

  That's no longer the case and doing `Rational(0.45, 86400)` would
  now perfectly work fine.

- Fixes #34008

Ruby uses the original method name, so will show the __temp__ method
name in the backtrace. However, in the common case the method name
is compatible with the `def` keyword, so we can avoid the __temp__
method name in that case to improve the name shown in backtraces
or TracePoint#method_id.

Deprecate Unicode#downcase/upcase/swapcase.

Use String methods directly instead.

Check that options passed to the to_json are passed to all objects that
respond to as_json.

Add test retries for railties