this fixes a failing test case

The note regarding the `_prefix` and `_suffix` options is no longer
useful since they were renamed specifically for this purpose.

Also the given example doesn't show what these options enable and in
which case they are really useful (when there are conflicting values
for instance).

Refs #20999.

[Godfrey Chan & Robin Dupret]

This makes it more clear that they are reserved keywords and also it
seems less redundant as the line already starts with the call to the
`enum` method.

Documentation had extra colon after keyword.

ActiveRecord::RecordNotFound modified to store model name, primary_key
and id of the caller model. It allows the catcher of this exception to make
a better decision to what to do with it. For example consider this simple
example:

    class SomeAbstractController < ActionController::Base
      rescue_from ActiveRecord::RecordNotFound, with: :redirect_to_404

      private def redirect_to_404(e)
        return redirect_to(posts_url) if e.model == 'Post'
        raise
      end
    end

Previously `has_one` and `has_many` associations were using the
`one` and `many` keys respectively. Both of these keys have special
meaning in I18n (they are considered to be pluralizations) so by
renaming them to `has_one` and `has_many` we make the messages more
explicit and most importantly they don't clash with linguistical
systems that need to validate translation keys (and their
pluralizations).

The `:'restrict_dependent_destroy.one'` key should be replaced with
`:'restrict_dependent_destroy.has_one'`, and
`:'restrict_dependent_destroy.many'` with
`:'restrict_dependent_destroy.has_many'`.

[Roque Pinel & Christopher Dell]

This clears the transaction record state when the transaction finishes
with a `:committed` status.

Considering the following example where `name` is a required attribute.
Before we had `new_record?` returning `true` for a persisted record:

```ruby
  author = Author.create! name: 'foo'
  author.name = nil
  author.save        # => false
  author.new_record? # => true
```

As per the docs, `mark_for_destruction` should do nothing if `autosave`
is not set to true. We normally persist associations on a record no
matter what if the record is a new record, but we were always skipping
records which were `marked_for_destruction?`.

Fixes #20882

I wrote a utility that helps find areas where you could optimize your program using a frozen string instead of a string literal, it's called [let_it_go](https://github.com/schneems/let_it_go). After going through the output and adding `.freeze` I was able to eliminate the creation of 1,114 string objects on EVERY request to [codetriage](codetriage.com). How does this impact execution?

To look at memory:

```ruby
require 'get_process_mem'

mem = GetProcessMem.new
GC.start
GC.disable
1_114.times { " " }
before = mem.mb

after = mem.mb
GC.enable
puts "Diff: #{after - before} mb"

```

Creating 1,114 string objects results in `Diff: 0.03125 mb` of RAM allocated on every request. Or 1mb every 32 requests.

To look at raw speed:

```ruby
require 'benchmark/ips'

number_of_objects_reduced = 1_114

Benchmark.ips do |x|
  x.report("freeze")    { number_of_objects_reduced.times { " ".freeze } }
  x.report("no-freeze") { number_of_objects_reduced.times { " " } }
end
```

We get the results

```
Calculating -------------------------------------
              freeze     1.428k i/100ms
           no-freeze   609.000  i/100ms
-------------------------------------------------
              freeze     14.363k (± 8.5%) i/s -     71.400k
           no-freeze      6.084k (± 8.1%) i/s -     30.450k
```

Now we can do some maths:

```ruby
ips = 6_226k # iterations / 1 second
call_time_before = 1.0 / ips # seconds per iteration 

ips = 15_254 # iterations / 1 second
call_time_after = 1.0 / ips # seconds per iteration 

diff = call_time_before - call_time_after

number_of_objects_reduced * diff * 100

# => 0.4530373333993266 miliseconds saved per request
```

So we're shaving off 1 second of execution time for every 220 requests. 

Is this going to be an insane speed boost to any Rails app: nope. Should we merge it: yep. 

p.s. If you know of a method call that doesn't modify a string input such as [String#gsub](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37) please [give me a pull request to the appropriate file](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37), or open an issue in LetItGo so we can track and freeze more strings. 

Keep those strings Frozen

![](https://www.dropbox.com/s/z4dj9fdsv213r4v/let-it-go.gif?dl=1)

Since the counter cache was properly being updated, the model became
stale. Simply reloading the model before attempting to destroy is
sufficient for this case. I believe this is enough of an edge case to be
a valid change to the tests, even though it represents a potential
breaking change.

Also removes a false positive test that depends on the fixed bug:

At this time, counter_cache does not work with polymorphic relationships
(which is a bug). The test was added to make sure that no
StaleObjectError is raised when the car is destroyed. No such error is
currently raised because the lock version is not incremented by
appending a wheel to the car.

Furthermore, `assert_difference` succeeds because `car.wheels.count`
does not check the counter cache, but the collection size. The test will
fail if it is replaced with `car.wheels_count || 0`.

This code is so fucked. Things that cause this bug not to replicate:

- Defining the validation before the association (we end up calling
  `uniq!` on the errors in the autosave validation)
- Adding `accepts_nested_attributes_for` (I have no clue why. The only
  thing it does that should affect this is adds `autosave: true` to the
  inverse reflection, and doing that manually doesn't fix this).

This solution is a hack, and I'm almost certain there's a better way to
go about it, but this shouldn't cause a huge hit on validation times,
and is the simplest way to get it done.

Fixes #20874.

Since nested hashes are also instances of
`ActionController::Parameters`, and we're explicitly looking to work
with a hash for nested attributes, this caused breakage in several
points.

This is the minimum viable fix for the issue (and one that I'm not
terribly fond of). I can't think of a better place to handle this at the
moment. I'd prefer to use some sort of solution that doesn't special
case AC::Parameters, but we can't use something like `to_h` or `to_a`
since `Enumerable` adds both.

While I've added a trivial test case for verifying this fix in
isolation, we really need better integration coverage to prevent
regressions like this in the future. We don't actually have a lot of
great places for integration coverage at the moment, so I'm deferring it
for now.

Fixes #20922.

We deprecate the support for passing an argument to force reload in
6eae366d. That led to several
deprecation warning when running Active Record test suite.

This commit silence the warnings by properly calling `#reload` on the
association proxy or on the association object instead. However, there
are several places that `ActiveSupport::Deprecation.silence` are used as
those tests actually tests the force reload functionality and will be
removed once `master` is targeted next minor release (5.1).

This is to simplify the association API, as you can call `reload` on the
association proxy or the parent object to get the same result.

For collection association, you can call `#reload` on association proxy
to force a reload:

    @user.posts.reload   # Instead of @user.posts(true)

For singular association, you can call `#reload` on the parent object to
clear its association cache then call the association method:

    @user.reload.profile   # Instead of @user.profile(true)

Passing a truthy argument to force association to reload will be removed
in Rails 5.1.

This reverts commit bdc1d329.

Before:
Calculating -------------------------------------
                        22.000  i/100ms
-------------------------------------------------
                        229.700  (± 0.4%) i/s -      1.166k
Total Allocated Object: 9939

After:
Calculating -------------------------------------
                        24.000  i/100ms
-------------------------------------------------
                        246.443  (± 0.8%) i/s -      1.248k
Total Allocated Object: 7939

```
begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  # gem 'rails', github: 'rails/rails', ref: 'bdc1d329'
  gem 'rails', github: 'rails/rails', ref: 'd2876141'
  gem 'arel', github: 'rails/arel'
  gem 'sqlite3'
  gem 'benchmark-ips'
end

require 'active_record'
require 'benchmark/ips'

ActiveRecord::Base.establish_connection('sqlite3::memory:')

ActiveRecord::Migration.verbose = false

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

class User < ActiveRecord::Base
  default_scope { where(admin: true) }
end

admin = true

1000.times do
  attributes = {
    name: "Lorem ipsum dolor sit amet, consectetur adipiscing elit.",
    email: "foobar@email.com",
    admin: admin
  }

  User.create!(attributes)

  admin = !admin
end

GC.disable

Benchmark.ips(5, 3) do |x|
  x.report { User.all.to_a }
end

key =
  if RUBY_VERSION < '2.2'
    :total_allocated_object
  else
    :total_allocated_objects
  end

before = GC.stat[key]
User.all.to_a
after = GC.stat[key]
puts "Total Allocated Object: #{after - before}"
```

The concurrent-ruby gem is a toolset containing many concurrency
utilities. Many of these utilities include runtime-specific
optimizations when possible. Rather than clutter the Rails codebase with
concurrency utilities separate from the core task, such tools can be
superseded by similar tools in the more specialized gem. This commit
replaces `ActiveSupport::Concurrency::Latch` with
`Concurrent::CountDownLatch`, which is functionally equivalent.

When preload is used in a default scope the preload_values were
returning nested arrays and causing the preloader to fail because it
doesn't know how to deal with nested arrays. So before calling preload!
we need to splat the arguments.

This is not needed to includes because it flatten its arguments.

as #uniq will be removed from Rails 5.0 as per the Active Support
exception raised:

ActiveSupport::DeprecationException: DEPRECATION WARNING: uniq is
deprecated and will be removed from Rails 5.0 (use distinct instead).

Not much of a thought leader if I can't spell it correctly 😉

After 908cfef6 was introduced fixtures that did not set an enum would
return nil instead of the default enum value.

The fixtures should assume the default if a different enum is not
defined.

The change checks first if the enum is defined in the fixture before
setting it based on the fixture.

The changes introduced to through associations in c80487eb were quite
interesting. Changing `relation.merge!(scope)` to `relation =
relation.merge(scope)` should in theory never cause any changes in
behavior. The subtle breakage led to a surprising conclusion.

The old code wasn't doing anything! Since `merge!` calls
`instance_exec` when given a proc, and most scopes will look something
like `has_many :foos, -> { where(foo: :bar) }`, if we're not capturing
the return value, it's a no-op. However, removing the `merge` causes
`unscope` to break.

While we're merging in the rest of the chain elsewhere, we were never
merging in `unscope` values, causing a breakage on associations where a
default scope was being unscoped in an association scope (yuk!). This is
subtly related to #20722, since it appears we were previously relying on
this mutability.

Fixes #20721.
Fixes #20727.

Closes #20743.

The task `db:_dump` now only dumps the schema if
`ActiveRecord::Base.dump_schema_after_migration` is true. This has
effects:

- `db:migrate:up`
- `db:migrate:down`
- `db:forward`
- `db:rollback`

These classes are part of Active Record Preloader, which is not part of
the public API.

With this change, we will always assume the association name is the same
as the table it's referencing. This is subtly different than treating
the hash key passed to `where` as the table name, as it still allows the
class referenced by the association to provide additional type
information.

After exploring several possible solutions to the ambiguity problem, I
do not think there is a short term answer that will maintain backwards
compatibility.

This change will make it so the following code does not work:

    class User
      has_many :approved_posts, -> { where(approved: true) }, class_name: "Post"
    end

    User.where(approved_posts: { id: 1 })

But prevents potential ambiguity and collision as demonstrated in [this
gist](https://gist.github.com/senny/1ae4d8ea7b0e269ed7a0).

Unfortunately, truely solving this requires significantly
re-architecting this code, so that what is currently represented as an
`Arel::Attribute` is instead another data structure that also references
the association it is representing, so we can identify the proper table
name for aliasing when we construct the final tree.

While I'd still like to accomplish that in the long run, I don't think
I'll be able to get there in time for Rails 5 (since I'm not full time
OSS any more, and this is several weeks worth of work). I'm hoping to
achieve this for Rails 5.1.

Fixes #20308

This is to show users that they can chain `.uniq` and `.pluck` to get
the `DISTINCT column` result. They don't have to do `DISTINCT column`
themselves.

Passing `:from` and `:to` to `change_column_default` makes this command
reversible as user has defined its previous state.

So, instead of having the migration command as:

    change_column_default(:posts, :state, "draft")

They can write it as:

    change_column_default(:posts, :state, from: nil, to: "draft")

fix tests