Since #29504, mysql2 adapter lost ability to insert zero value on
primary key due to enforce `NO_AUTO_VALUE_ON_ZERO` disabled.
That is for using `DEFAULT` on auto increment column, but we can use
`NULL` instead in that case.

Lock Minitest 5.11.1

To workaround `undefined method `error?' for` reported
at https://travis-ci.org/rails/rails/jobs/333456146

Update note on MySQL index order support [ci skip]

MySQL supports descending indexes from 8.0.1 onwards:
https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-1.html

Clarify autoload_paths and eager_load in guides per current usage.

Since #31422, `insert_fixtures` is deprecated.

It was unused since 9e4c41c9.

Fix typo in API document FormHelper#fields

- Fix typo
- Adjust output example to other example's format

It is useless since 90c8be76.

This is a regression caused by 6beb4de7.

In PostgreSQL, ORDER BY expressions must appear in SELECT list when
using DISTINCT.

When using `count(:all)` with eager loading, Active Record enforces
DISTINCT to count the driving table records only. 6beb4de7 was caused the
regression because `count(:all)` with DISTINCT path no longer removes
ORDER BY.

We need to ignore ORDER BY when DISTINCT is enforced, otherwise not
always generated valid SQL for PostgreSQL.

Fixes #31783.

Clear the transaction state when AR object is duped

Avoid passing unnecessary arguments to relation

Only enable verbose_query_logs in Rails server

Remove code duplication for `ActionController::Metal.action`

Most of the time the table and predicate_builder
passed to Relation.new are exactly the
arel_table and predicate builder of the
given klass. This uses klass.arel_table
and klass.predicate_builder as the defaults,
so we don't have to pass them in most cases.

This does change the signaure of both Relation and
AssocationRelation. Are we ok with that?

It doesn't have to do anything, but it shouldn't fail.

Fixes #31766.

Postgresql bulk_change_table should flatten procs array

Build a multi-statement query when inserting fixtures

* Add backticks
* Expand tabs
* Fix indentation

* rDBMS -> RDBMS. There is only place using rDBMS.
* a SQL -> an SQL

* Update active_record_basics.md

I made a bit of clarification for people, who are not familiar with SQL (pretty much like me). However, I don't know what tutorial for MySQL is better, so I haven't inserted a link yet.

* [ci skip] For those who new to GitHub

Added more instructions for contributing guides. Without them, it was somewhat confusing for me to find what I should actually do.

* Update active_record_basics.md

Fixed grammar and text wrapping as requested.

* Update contributing_to_ruby_on_rails.md

Revised instructions.

* Update contributing_to_ruby_on_rails.md

Typos

* Update active_record_basics.md

* [ci skip] Update active_record_basics

Added a few links to SQL tutorials found on the net.
Also, changed MySQL to SQL (or one of its extensions) - I think that it's a good compromise.

* [ci skip] I think now it's more clear what to do.

* [ci skip] Fixed strings

[Rafael Mendonça França + loothunter1]

Allow for custom handling of exceptions that are discarded

We don't implement much custom marshalling logic for these objects, but
the proc default case needs to be handled separately. Unfortunately
there's no way to just say "do what you would have done but with this
value for one ivar", so we have to manually implement `marshal_load` as
well.

The test case is a little bit funky, but I'd really like an equality
test in there, and there's no easy way to add one now that this is out
of AR (since the `attributes` method isn't here)

Fixes #31216

Fix actionmailer lambda default

- mysql will add a 2 bytes margin to the statement, so given a `max_allowed_packet` set to 1024 bytes, a 1024 bytes fixtures will no be inserted (mysql will throw an error)
- Preventing this by decreasing the max_allowed_packet by 2 bytes when doing the comparison with the actual statement size

Should fix #31688 unless someone can point me to a better way to achieve
this goal. Essentially David's point was that verbose query logging when
enabled in Rails console tends to make things very noisy.

That's especially true if we display absolute paths to callsites which
sadly is still the case when we detect a caller that isn't part of the
Rails application — think gems.

Discussed this with both @matthewd and @rafaelfranca and went back and
forth between enabling if defined?(Rails::Server) or this implementation
and this one makes more sense for now.

Long term I think it'll make sense to let people override this default
disabling in Rails Console because they might want to use the feature
but for now it feels like the correct default behavior.

Fix locale_selector JS bug in ActionMailer Preview

Improve fault tolerance for redis cache store