Exclude missing marshal_dump and _dump methods from being delegated to
an object's delegation target via the delegate_missing_to extension.
This avoids unintentionally adding instance variables to an object
during marshallization, should the delegation target be a method which
would otherwise add them.

In current versions of Ruby, a bug exists in the way objects are
marshalled, allowing for instance variables to be added or removed
during marshallization (see https://bugs.ruby-lang.org/issues/15968).
This results in a corrupted serialized byte stream, causing an object's
instance variables to "leak" into subsequent serialized objects during
demarshallization.

In Rails, this behavior may be triggered when marshalling an object that
uses the delegate_missing_to extension, if the delegation target is a
method which adds or removes instance variables to an object being
marshalled - when calling Marshal.dump(object), Ruby's built in behavior
will check whether the object responds to :marshal_dump or :_dump, which
in turn triggers the delegation target method in the
responds_to_missing? function defined in
activesupport/lib/active_support/core_ext/module/delegation.rb

While future versions of Ruby will resolve this bug by raising a
RuntimeError, the underlying cause of this error may not be readily
apparent when encountered by Rails developers. By excluding marshal_dump
and _dump from being delegated to an object's target, this commit
eliminates a potential cause of unexpected behavior and/or
RuntimeErrors.

Fixes #36522

Move the deprecation call after the new class has been defined:

Assigning to a collection of attachments appends rather than replacing, as in 5.2. Existing 5.2 apps that rely on this behavior will no longer break when they're upgraded to 6.0.

For apps generated on 6.0 or newer, assigning replaces the existing attachments in the collection. #attach should be used to add new attachments to the collection without removing existing ones.

I expect that we'll deprecate the old behavior in 6.1.

Closes #36374.

[ActiveRecord] Deduplicate optimizer hints

Revert "Make UTF-8 string requirement explicit for `ActiveSupport::Inflector.transliterate`"

Make UTF-8 string requirement explicit for `ActiveSupport::Inflector.transliterate`

Fix Loadable.exclude_from to also reset Kernel#require

Fix problem with accessing deprecated constant proxy's subclass

In older Ruby, nil, Symbol, Fixnum, Rational, and Complex were not
duplicable. In Ruby 2.5, all of them are duplicable.

Remove dead code in duplicable.rb

Fix activestorage CI failure due to ffprove version differece

Delete mention of Ruby 1.9 [skip ci]

Prevent exception of loading database yaml with blank config file

Most of this section was written from the time that render file: was the
default, before CVE-2016-0752.

This updates the guide to the Rails 6 `render file:` behaviour, moves it
to a more appropriate part of the file.

[ci skip]

Most of these examples no longer work. The ability to render an absolute
path was removed as part of CVE-2016-0752. In Rails 6 we changed `render
file:` to only take exact paths and always to render them as raw files.
Rendering a template with its extensions _is_ supported, but I don't
think should be recommended.

This also removes `render file:` from an example where it isn't
relevant.

[ci skip]

All this has been simplified.

Merge pull request #36647 from giraffate/fix_exists_with_distinct_and_offset_and_order_in_postgresql

Fix `relation.exists?` with giving `distinct`, `offset` and `order` for joined table

Share the Arel dispatch cache between connections

Share the column and table name quote cache between connections

update example url for add_source

[ci skip]

MySQL: Check error number instead of a message

Fix query cache when using shared connections

Make "bin/setup" works when using PostgreSQL with locales other than en locale

Fix Identation

[ci skip]

ref https://github.com/rails/rails/pull/36621#discussion_r301208961

(Backport 6-0-stable) Add database_exists? method to connection adapters

When SQLite connects it will silently create a database if the database does not
exist. This behaviour causes different issues because of inconsistent behaviour
between adapters: #36383, #32914. This commit adds a `database_exists?` method
as a way to check the database without creating it. This is a stepping stone to
fully resolving the above issues.

When DATABASE_URL is specified don't trample envs that use a url: key

Do not use aliases in GROUP BY clause

MySQL: Fix schema dumping `enum` and `set` columns correctly

Fixes that file attachments without captions would not be represented in plain text generated from rich-text content, causing ActionText::RichText#present? to return false.

Closes #36607.

Fix Browser#preload for older Selenium

Preload browser driver_path to fix system testing under parallelism