Fix 'Getting Started with Rails' [ci skip]

Add missing spaces [ci skip]

  `bin/rails generate controller Comments` creates files
  app/assets/javascripts/comments.coffee
  app/assets/stylesheets/comments.scss
  not
  app/assets/javascripts/comment.coffee
  app/assets/stylesheets/comment.scss

Clear query cache during checkin, instead of an execution callback

Avoid `unscope(:order)` when `limit_value` is presented for `count`

If `limit_value` is presented, records fetching order is very important
for performance. Should not unscope the order in the case.

remove unused require

Use local variable instead of instance variable [ci skip]

Update render yield docs to use `search` local variable instead of `@q` instance variable

2.3: sprintf('%0.1f', 5.55)  #=> "5.5"
2.4: sprintf('%0.1f', 5.55)  #=> "5.6"

see: https://github.com/ruby/ruby/commit/6ed8c79ddb11ccfb580bb0a22b22cc1362250255 and
https://github.com/ruby/ruby/commit/295f60b94d5ff6551fab7c55e18d1ffa6a4cf7e3

this test case fails with ruby 2.4, so we want to see what's actually happening

YAML and ERB were removed at 971d5107

Use different name for main and thread connection variable.

Under JRuby, the updates of the one shared variable interleaved,
causing threads to pick up each others' connections. I'm amazed
this worked on MRI.

Update sqlite3

change `MemCacheStore#increment` and `MemCacheStore#decrement` to public API [ci skip]

If the call to `.define_attribute_methods` actually ends up loading the
schema (*very* hard to do, as it requires the object being created
without `allocate` having been called, but it can be done by manually
calling `initialize` from inside `marshal_load` if you're crazy), the
value of `_default_attributes` will change from that call.

Move `test_quoting_classes` into `test/cases/quoting_test.rb`

fix datatime error

* Fixes TypeError when cache counter value equals nil

* Test case for counter cache on unloaded has_many association

remove warning from railtie

This removes the following warnings.

```ruby
rails/railties/lib/rails/railtie.rb:186: warning: instance variable @rake_tasks not initialized
rails/railties/lib/rails/railtie.rb:186: warning: instance variable @rake_tasks not initialized
rails/railties/lib/rails/railtie.rb:186: warning: instance variable @load_console not initialized
rails/railties/lib/rails/railtie.rb:186: warning: instance variable @rake_tasks not initialized
```

Don't put db:migrate and db:setup in binfiles if activerecord is excluded

Remove unnecessary `target.uniq.size` in `CollectionAssociation#size`

Remove unused internal `:dependent` option in `CollectionAssociation#delete`

With the changes in #25337, double save bugs are pretty much impossible,
so we can just lift this restriction with pretty much no change. There
were a handful of cases where we were relying on specific quirks in
tests that had to be updated. The change to has_one associations was due
to a particularly interesting test where an autosaved has_one
association was replaced with a new child, where the child failed to
save but the test wanted to check that the parent id persisted to `nil`.

I think this is almost certainly the wrong behavior, and I may change
that behavior later. But ultimately the root cause was because we never
remove the parent in memory when nullifying the child. This makes #23197
no longer needed, but it is what we'll do to fix some issues on 5.0

Close #23197

Deprecate the behavior of AR::Dirty inside of after_(create|update|save) callbacks

We pretty frequently get bug reports that "dirty is broken inside of
after callbacks". Intuitively they are correct. You'd expect
`Model.after_save { puts changed? }; model.save` to do the same thing as
`model.save; puts model.changed?`, but it does not.

However, changing this goes much farther than just making the behavior
more intuitive. There are a _ton_ of places inside of AR that can be
drastically simplified with this change. Specifically, autosave
associations, timestamps, touch, counter cache, and just about anything
else in AR that works with callbacks have code to try to avoid "double
save" bugs which we will be able to flat out remove with this change.

We introduce two new sets of methods, both with names that are meant to
be more explicit than dirty. The first set maintains the old behavior,
and their names are meant to center that they are about changes that
occurred during the save that just happened. They are equivalent to
`previous_changes` when called outside of after callbacks, or once the
deprecation cycle moves.

The second set is the new behavior. Their names imply that they are
talking about changes from the database representation. The fact that
this is what we really care about became clear when looking at
`BelongsTo.touch_record` when tests were failing. I'm unsure that this
set of methods should be in the public API. Outside of after callbacks,
they are equivalent to the existing methods on dirty.

Dirty itself is not deprecated, nor are the methods inside of it. They
will only emit the warning when called inside of after callbacks. The
scope of this breakage is pretty large, but the migration path is
simple. Given how much this can improve our codebase, and considering
that it makes our API more intuitive, I think it's worth doing.

fixing @generators var initialization

pre initializing variables values

Changing from var init to symbol to instance var get/set

fix typo in Rails Test Runner section