/cc @fxn

/cc @fxn

Add `null` option to timestamps as migration generator does [ci skip]

Re-enable capture'ing non-String values

This has been discussed in #17661 and partially reverts the changes made
in 9de83050 and 986cac73

The test case added to content_for acts as a regression / acceptance test.

Allow URL helpers to work with optional scopes

ParameterFilter shouldn't try to dup symbol keys

Pass connection rather than alias_tracker

Fix handling of positional url helper arguments when format is false

There is no need to subtract one from the path_params size when there is
no format parameter because it is not present in the path_params array.

Fixes #17819.

Because we're only using the `connection` so passing the entire tracker
isn't unnecessary.

Eventually only the `connection` will be passed to `add_constraints`
with later refactoring but curretly that's not possible because of
`construct_tables` method.

[guides] Fix method name inconsistency in a mailer example

[ci skip]

Use redis protocol

Add AC::Parameters#to_unsafe_h

Closes #17965, #17968

[Godfrey Chan, Miklós Fazekas]

I'm not sure what's the use case for this, but apparently it broke some apps.
Since it was not the intended result from #16210 I fixed it to not raise an
exception anymore. However, I didn't add documentation for it because I don't
know if this should be officially supported without knowing how it's meant to
be used.

In general, validations should be side-effect-free (other than adding to the
error message to `@errors`). Order-dependent validations seems like a bad idea.

Fixes #18002

See 63462ec9

Make AC::Params.permit_all_parameters thread safe

Fix default queue name prefix delimiter

Now displays as underscore, and not an empty string, when converted from markdown to HTML.
Escaped the underscore per http://daringfireball.net/projects/markdown/syntax#em
Fixes rails/rails#18009