Did you forget to commit the function?

Should this maybe be prompt_hostname? Simply for discoverability, and to match prompt_pwd?

Did you forget to commit the function?

Oops, yes, stupid git commit -a doesn't include new files. Fixed.

Is splitting on '.' from hostname output always equivalent to using hostname -s?

(I genuinely have no idea.)

Should this maybe be prompt_hostname? Simply for discoverability, and to match prompt_pwd?

Agreed. Changed.

Is splitting on '.' from hostname output always equivalent to using hostname -s?

It's supposed to be since the definition of hostname -s is to convert a FQDN to a simple host name.

In no case can the FQDN be something like "www.mysite.com" and hostname -s and the simple host name be "myserver"? That'd be my only worry if it's possible, it'd now output "www".

If by simple host name you mean what is returned as the nodename by the uname(3) then "yes" in theory. In practice probably not because a) that value is supposed to be the network name and should match whatever gethostname() returns. If it doesn't the system is misconfigured and that isn't our problem.

Is splitting on ',' from hostname output always equivalent to using hostname -s?

First of all, that's what we currently do, so there's no regression here. Secondly, this allows us to fix it in one place if we ever figure out a better solution.

Thirdly: Probably not. This is probably one of those things where there's a super-rare super-complicated edge case that some people get really passionate about (maybe some way to make it recursive, or dependent on locale?). We'll get an issue and then we can work it out. Or they can just override the function.

First of all, that's what we currently do, so there's no regression here

We used to use hostname -s here:

   # Just calculate these once, to save a few cycles when displaying the prompt
    if not set -q __fish_prompt_hostname
        set -g __fish_prompt_hostname (hostname -s)
    end

Yeah, but in the other prompts we didn't. This was inconsistent.

It looks like most of the sample prompts are not using this.

Er, I'm totally mistaken. I was on Integration_2.4.0 and thought I was on master. And I mistakenly pushed two commits I shouldn't have. Reverting.