wp-signup.php with `new` in the query string results in a "site does not exist" message even if the site does exist

[henry.wright]

Steps to reproduce:

1. Visit example.com/wp-signup.php?new=sport where sport is the address of an existing site in your network. Note I'm using sport as an example. You should replace sport with the address of an existing blog in your network.

You will get the following message appear on the page:

The site you were looking for, ​https://sport.example.com/, does not exist, but you can create it now!

[henry.wright]

To add, the network install I used to test allows both user and blog registrations

[henry.wright]

53355.diff uses domain_exists() to check if a site name is already taken before outputting the message.

[henry.wright]

53355.2.diff fixes the value of $domain which is passed to domain_exists() as the first param.

[henry.wright]

53355.3.diff ensures the right parts of the extracted host name are used to build the domain value.

[SergeyBiryukov]

Related: #53348

[henry.wright]

53355.4.diff adds a separation character when building the domain value

[henry.wright]

Related #54290

[audrasjb]

As per today's bug scrub and since this ticket needs to be refreshed against trunk and properly tested, let's move it to next milestone.

[kirasong]

Checked into this ticket in ​a bug scrub today, and here's a synopsis of the suggestions to move things forward:

Looks like the patch applies at the moment, so removing needs-refresh.

Tests would be helpful, so adding needs-unit-tests as well.

This PR aims to fix the problem outlined in ticket 53355 but also validates the field right away, so if a name of an existing blog is sent via the query string, the user will see an error in the first page load.

Trac ticket: https://core.trac.wordpress.org/ticket/53355

[costdev]

With 6.0 RC1 tomorrow and the patch still needing testing, I'm moving this ticket to the 6.1 milestone.

[audrasjb]

Unfortunately, this ticket didn’t get more momentum in 6.1 than in 6.0… sorry about that, but the proposed patch still needs testing, so let's move it to Future Release milestone, at least until it's properly reviewed by a Network component maintainer.