* WIP: Add credentials using a generic EncryptedConfiguration class

This is sketch code so far.

* Flesh out EncryptedConfiguration and test it

* Better name

* Add command and generator for credentials

* Use the Pathnames

* Extract EncryptedFile from EncryptedConfiguration and add serializers

* Test EncryptedFile

* Extract serializer validation

* Stress the point about losing comments

* Allow encrypted configuration to be read without parsing for display

* Use credentials by default and base them on the master key

* Derive secret_key_base in test/dev, source it from credentials in other envs

And document the usage.

* Document the new credentials setup

* Stop generating the secrets.yml file now that we have credentials

* Document what we should have instead

Still need to make it happen, tho.

* [ci skip] Keep wording to `key base`; prefer defaults.

Usually we say we change defaults, not "spec" out a release.

Can't use backticks in our sdoc generated documentation either.

* Abstract away OpenSSL; prefer MessageEncryptor.

* Spare needless new when raising.

* Encrypted file test shouldn't depend on subclass.

* [ci skip] Some woordings.

* Ditch serializer future coding.

* I said flip it. Flip it good.

* [ci skip] Move require_master_key to the real production.rb.

* Add require_master_key to abort the boot process.

In case the master key is required in a certain environment
we should inspect that the key is there and abort if it isn't.

* Print missing key message and exit immediately.

Spares us a lengthy backtrace and prevents further execution.

I've verified the behavior in a test app, but couldn't figure the
test out as loading the app just exits immediately with:

```
/Users/kasperhansen/Documents/code/rails/activesupport/lib/active_support/testing/isolation.rb:23:in `load': marshal data too short (ArgumentError)
	from /Users/kasperhansen/Documents/code/rails/activesupport/lib/active_support/testing/isolation.rb:23:in `run'
	from /Users/kasperhansen/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/minitest-5.10.2/lib/minitest.rb:830:in `run_one_method'
	from /Users/kasperhansen/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/minitest-5.10.2/lib/minitest/parallel.rb:32:in `block (2 levels) in start'
```

It's likely we need to capture and prevent the exit somehow.
Kernel.stub(:exit) didn't work. Leaving it for tomorrow.

* Fix require_master_key config test.

Loading the app would trigger the `exit 1` per require_master_key's
semantics, which then aborted the test.

Fork and wait for the child process to finish, then inspect the
exit status.

Also check we aborted because of a missing master key, so something
else didn't just abort the boot.

Much <3 to @tenderlove for the tip.

* Support reading/writing configs via methods.

* Skip needless deep symbolizing.

* Remove save; test config reader elsewhere.

* Move secret_key_base check to when we're reading it.

Otherwise we'll abort too soon since we don't assign the secret_key_base
to secrets anymore.

* Add missing string literal comments; require unneeded yaml require.

* ya ya ya, rubocop.

* Add master_key/credentials after bundle.

Then we can reuse the existing message on `rails new bc4`.

It'll look like:

```
Using web-console 3.5.1 from https://github.com/rails/web-console.git (at master@ce985eb)
Using rails 5.2.0.alpha from source at `/Users/kasperhansen/Documents/code/rails`
Using sass-rails 5.0.6
Bundle complete! 16 Gemfile dependencies, 72 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
Adding config/master.key to store the master encryption key: 97070158c44b4675b876373a6bc9d5a0

Save this in a password manager your team can access.

If you lose the key, no one, including you, can access anything encrypted with it.

      create  config/master.key
```

And that'll be executed even if `--skip-bundle` was passed.

* Ensure test app has secret_key_base.

* Assign secret_key_base to app or omit.

* Merge noise

* Split options for dynamic delegation into its own method and use deep symbols to make it work

* Update error to point to credentials instead

* Appease Rubocop

* Validate secret_key_base when reading it.

Instead of relying on the validation in key_generator move that into
secret_key_base itself.

* Fix generator and secrets test.

Manually add config.read_encrypted_secrets since it's not there by default
anymore.

Move mentions of config/secrets.yml to config/credentials.yml.enc.

* Remove files I have no idea how they got here.

* [ci skip] swap secrets for credentials.

* [ci skip] And now, changelogs are coming.

PERF: Incorrect memoization in `ActiveRecord::Associations::Preloader…

```
require 'active_record'
require 'benchmark/ips'

ActiveRecord::Base.establish_connection(ENV.fetch('DATABASE_URL'))
ActiveRecord::Migration.verbose = false

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name, :email
    t.integer :topic_id
    t.timestamps null: false
  end

  create_table :topics, force: true do |t|
    t.string :title
    t.timestamps null: false
  end
end

attributes = {
  name: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
  email: 'foobar@email.com'
}

class Topic < ActiveRecord::Base
  has_many :users
end

class User < ActiveRecord::Base
  belongs_to :topic
end

100.times do
  User.create!(attributes)
end

users = User.first(50)

100.times do
  Topic.create!(title: 'This is a topic', users: users)
end

Benchmark.ips do |x|
  x.config(time: 10, warmup: 5)

  x.report("preload") do
    User.includes(:topic).all.to_a
  end
end
```

```
Calculating -------------------------------------
             preload    25.000  i/100ms
-------------------------------------------------
             preload    251.772  (± 1.2%) i/s -      2.525k
```

```
Calculating -------------------------------------
             preload    26.000  i/100ms
-------------------------------------------------
             preload    270.392  (± 1.1%) i/s -      2.704k
```

Remove not used gems by default [ci skip]

`rack-mount` switched to journey with 5f0b37c4.
Also, `rack-cache` will not be used unless you explicitly specify it.

Ref:
https://github.com/rails/rails/commit/037e50ec39c7c3d58a102a6584e2740652420d1d
https://github.com/rails/rails/commit/1fc795468525d8622cdca474a54c8310a514aa46

Remove needless `silence_warnings`

Since ff30db13, warning is not shown.

Reorganize secrets test to use only `isolation/abstract_unit`

Do not install unused gem

PERF: Recover `ActiveRecord::pluck` performance.

This method was moved from `JoinHelper` in 0fddc3c1, but it is only used
for `table.create_join` in the internal and `Nodes::InnerJoin` is
default join klass. So it is not needed to pass it explicitly.

`qu-redis` is need for qu adapter test.
However, since 8ecc5ab1, qu adapter test has not been executed,
it is unnecessary now.

The superclass (`MacroReflection`) already have the same method
definition.

`primary_key_type` is no longer used since #26718.
`quoted_table_name` is no longer used since Rails 3.1.

Fixes #30539.

Currently, secrets test uses `abstract_unit` and `isolation/abstract_unit`.
This is a bit odd. Therefore, reorganize it so that use only
`isolation/abstract_unit`.

Context: https://github.com/rails/rails/pull/30520#issuecomment-327409586

CI against JRuby 9.1.13.0

http://jruby.org/2017/09/06/jruby-9-1-13-0.html

Because `table` is part of `reflection`, don't need to pass it
explicitly. And also, naming `alias_name` to `table` is a little
confusing. `aliased_table` is preferable than `alias_name`.

`PolymorphicReflection` is an internal class that is used in
`ThroughReflection`. But `RuntimeReflection` is used for the head of
chain in `AssociationScope`. These are totally different things.

The order of scope evaluation should be from through scope to the
association's own scope. Otherwise the association's scope cannot affect
to through scope.

Fixes #13677.
Closes #28449.

[ci skip]

fix type fully qualified [ci skip]

```ruby
require 'active_record'
require 'benchmark/ips'

ActiveRecord::Base.establish_connection(ENV.fetch('DATABASE_URL'))
ActiveRecord::Migration.verbose = false

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name, :email
    t.timestamps null: false
  end
end

attributes = {
  name: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
  email: 'foobar@email.com'
}

class User < ActiveRecord::Base; end

1000.times do
  User.create!(attributes)
end

Benchmark.ips do |x|
  x.config(time: 10, warmup: 2)

  x.report('pluck 1 column') do
    User.pluck(:id)
  end

  x.report('pluck 2 columns') do
    User.pluck(:id, :email)
  end

  x.report('pluck 1 column with scope') do
    User.where(id: 1000).pluck(:id)
  end

  x.report('pluck 2 columns with scope') do
    User.where(id: 1000).pluck(:id, :email)
  end
end
```

```
Calculating -------------------------------------
      pluck 1 column   122.000  i/100ms
     pluck 2 columns    74.000  i/100ms
pluck 1 column with scope
                       615.000  i/100ms
pluck 2 columns with scope
                       515.000  i/100ms
-------------------------------------------------
      pluck 1 column      1.272k (± 3.9%) i/s -     12.810k
     pluck 2 columns    750.096  (± 3.3%) i/s -      7.548k
pluck 1 column with scope
                          6.074k (± 4.1%) i/s -     60.885k
pluck 2 columns with scope
                          5.158k (± 2.7%) i/s -     52.015k
```

```
Calculating -------------------------------------
      pluck 1 column   126.000  i/100ms
     pluck 2 columns    78.000  i/100ms
pluck 1 column with scope
                       457.000  i/100ms
pluck 2 columns with scope
                       434.000  i/100ms
-------------------------------------------------
      pluck 1 column      1.266k (± 2.1%) i/s -     12.726k
     pluck 2 columns    795.061  (± 3.0%) i/s -      7.956k
pluck 1 column with scope
                          4.660k (± 2.1%) i/s -     46.614k
pluck 2 columns with scope
                          4.355k (± 2.3%) i/s -     43.834k
```

```
Calculating -------------------------------------
      pluck 1 column   126.000  i/100ms
     pluck 2 columns    78.000  i/100ms
pluck 1 column with scope
                       539.000  i/100ms
pluck 2 columns with scope
                       481.000  i/100ms
-------------------------------------------------
      pluck 1 column      1.308k (± 3.4%) i/s -     13.104k
     pluck 2 columns    798.604  (± 2.8%) i/s -      8.034k
pluck 1 column with scope
                          5.530k (± 3.4%) i/s -     55.517k
pluck 2 columns with scope
                          4.914k (± 2.7%) i/s -     49.543k
```

```
Calculating -------------------------------------
      pluck 1 column   139.000  i/100ms
     pluck 2 columns    79.000  i/100ms
pluck 1 column with scope
                       580.000  i/100ms
pluck 2 columns with scope
                       526.000  i/100ms
-------------------------------------------------
      pluck 1 column      1.337k (± 3.0%) i/s -     13.483k
     pluck 2 columns    806.776  (± 2.7%) i/s -      8.137k
pluck 1 column with scope
                          5.924k (± 4.1%) i/s -     59.160k
pluck 2 columns with scope
                          5.276k (± 3.1%) i/s -     53.126k
```

Normalize/process Cache-Control headers consistently

Do not pass an instance variable to a private method

`ActionView::Helpers::Tags::Base` has `@object` and
all passed arguments for

* `#value`
* `#value_before_type_cast`
* `#value_came_from_user?`

are `@object`, so we do not need to pass arguments in this case.

Run in-app rails commands via fork+load where possible

Because `refl.scope` is the same meaning with `chain_head.scope`.

Explicitly require `test_unit/reporter`

Add Documentation For Duration Support & Expiry Meta Data  Added to Signed / Encrypted Cookies

Because `reflection_scope.values` will create extra new hash.

If `reflection.scope` isn't given, `reflection_scope` is always
`klass.unscoped`. it is unnecessary to merge it.

Otherwise using reserved words as composite primary key names will be
failed as an invalid SQL.

Fixes #30518.

While this avoids shell argument parsing, we still pass through
everything in our stack.

* Documentation for Duration support added  to  signed/encrypted cookies

* Changelog entries for the duration support and expiry metadata added to cookies

[ci skip]