This logic was just doing duplicated work, since the button_to helper
relies on tag/content_tag to generate the button html, which already
handles all boolean attributes it knows about.

The code dates back to 2005: 43c470fa.

Reuse the CollectionAssociation#reader proxy cache if the foreign key is present from the start.

Conflicts:
	activerecord/CHANGELOG.md

Make example code consistent for better understanding. [ci skip]

Update old link in pessimistic.rb comments [ci skip]

Update link in comments to point to latest MySQL production version documentation. See here for reference: http://dev.mysql.com/doc/refman/5.0/en/choosing-version.html

Fix NullRelation.update_all and .exists? signature to match the same on Relation

Fix wrong model name for 'Articles', It should be 'Article' [ci skip]

- Also changed 'a' to 'an' for 'Article' word.

Compare content_type with Mime::XML instead of regexp

Skip the `:race_condition_ttl` branch if the option is 0 or nil.

Add config.active_record.dump_schemas.

Fixes db:structure:dump when using schema_search_path and PostgreSQL
extensions.

Closes #17157.

Drop `references_eager_loaded_tables?` test from `has_include?`

It is redundant with tests in `eager_loading?`, but for the difference
between `includes_values.present?` and `includes_values.any?`, which
is a difference without a distinction because `false` has no meaning
for `includes`.

Fix deprecation warning in rails_info_controller tests

Use keyword arguments in request methods

Remove unused variable in activerecord reflection_test.

[ci skip] reflection doc fix about hierarchy

Materialize subqueries by adding `DISTINCT` to suport MySQL 5.7.6 and later

Renaming transactional fixtures to transactional tests

I’m renaming all instances of `use_transcational_fixtures` to
`use_transactional_tests` and “transactional fixtures” to
“transactional tests”.

I’m deprecating `use_transactional_fixtures=`. So anyone who is
explicitly setting this will get a warning telling them to use
`use_transactional_tests=` instead.

I’m maintaining backwards compatibility—both forms will work.
`use_transactional_tests` will check to see if
`use_transactional_fixtures` is set and use that, otherwise it will use
itself. But because `use_transactional_tests` is a class attribute
(created with `class_attribute`) this requires a little bit of hoop
jumping. The writer method that `class_attribute` generates defines a
new reader method that return the value being set. Which means we can’t
set the default of `true` using `use_transactional_tests=` as was done
previously because that won’t take into account anyone using
`use_transactional_fixtures`. Instead I defined the reader method
manually and it checks `use_transactional_fixtures`. If it was set then
it should be used, otherwise it should return the default, which is
`true`. If someone uses `use_transactional_tests=` then it will
overwrite the backwards-compatible method with whatever they set.

Move Adapter to private constant

to support MySQL 5.7.6 `optimizer_switch='derived_merge=on'`

Adds more clarity on how to use custom rake tasks with arguments passed to it [ci skip]

Regexp is broken for both content types including charsets and for
integration tests, where the content_type is a Mime::Type and not String

When a new record has the necessary information prior to save, we can
avoid busting the cache.

We could simply clear the @proxy on #reset or #reset_scope, but that
would clear the cache more often than necessary.

[skip ci] Fix typos in guides

[skip ci] Fix typo in actionmailer documentation

[ci skip] Fix dead link

getting_started.html#the-mvc-architecture is lost by this commit
2f06c94e (Mar 14 2012 !).

So replace it with wikipedia link.

If there was a polymorphic hm:t association with a scope AND second
non-scoped hm:t association on a model the polymorphic scope would leak
through into the call for the non-polymorhic hm:t association.

This would only break if `hotel.drink_designers` was called before
`hotel.recipes`. If `hotel.recipes` was called first there would be
no problem with the SQL.

Before (employable_type should not be here):
```
SELECT COUNT(*) FROM "drink_designers" INNER JOIN "chefs" ON
"drink_designers"."id" = "chefs"."employable_id" INNER JOIN
"departments" ON "chefs"."department_id" = "departments"."id" WHERE
"departments"."hotel_id" = ? AND "chefs"."employable_type" = ?
[["hotel_id", 1], ["employable_type", "DrinkDesigner"]]
```

After:
```
SELECT COUNT(*) FROM "recipes" INNER JOIN "chefs" ON "recipes"."chef_id"
= "chefs"."id" INNER JOIN "departments" ON "chefs"."department_id" =
"departments"."id" WHERE "departments"."hotel_id" = ?  [["hotel_id", 1]]
```

From the SQL you can see that `employable_type` was leaking through when
calling recipes. The solution is to dup the chain of the polymorphic
association so it doesn't get cached. Additionally, this follows
`scope_chain` which dup's the `source_reflection`'s `scope_chain`.

This required another model/table/relationship because the leak only
happens on a hm:t polymorphic that's called before another hm:t on the
same model.

I am specifically testing the SQL here instead of the number of records
becasue the test could pass if there was 1 drink designer recipe for the
drink designer chef even though the `employable_type` was leaking through.
This needs to specifically check that `employable_type` is not in the SQL
statement.

add mailer suffix to comments for email previews