Introduce wp_is_trusted_network()

[jeremyfelt]

wp_is_trusted_network() is a first step in establishing the concepts around trusted and untrusted networks in multisite as part of the ​potential roadmap.

At first, the function will always return false. This will allow us to start plugging it into various parts of core to better determine how to call something "open" (as in registration, with untrusted users).

In the future, it will likely default to false with a filter to modify on a per network basis.

In 30071:

Introduce wp_is_trusted_network()

A first step to establish concepts around trusted and untrusted networks.

• Will always return false as default.
• Will one day have a filter.

Fixes #30145

Discussion points:

• Should this be moved out of ms-functions.php?
• Should it be renamed is_trusted_network() (minus the wp_ prefix) to match most of the other conditionals?

This function must always exist, and should by default return true for single installs, and false for multisite. No more global functions without a wp_ prefix, please. is_trusted_network() may have been used already, somewhere.

Then to determine on what conditions this should return true for multisite, like a constant, or a site option.

After that we can start implementing it to make multisite go in the direction we want.

Just my humble opinion, or my two cents, if you wish.

I agree with @johnbilion's 2 points.

I guess is_trusted_network() should return false in single site. Because developers can use is_multisite() to check multisite or not.