bug#48747: add project-name generic

[Dmitry Gutov <dgutov@yandex.ru>]

On 21.11.2022 00:17, Stephen Leake wrote:
> eglot builds a name for a server using the root directory of the
> project - in effect:
> 
> (file-name-base (directory-file-name (project-root (project-current))))
> 
> That name shows up in the elgot mode line, to tell the user which server
> the buffer is connected to, in progress report messages, and in the name
> of the EGLOT log buffer, which is useful for debugging things.
> 
> If the project root directory happens to have a meaningful name, that's
> fine. In my use cases, it's usually not meaningful. For example, I have
> two worktrees of my wisitoken project, one for the main branch, one for
> a work branch. The eglot names, and the ones I'd like to see, are:
> 
>      default     desired
>      "build"     "wisitoken main"
>      "build"     "wisitoken work"
> 
> Similarly, the name for the ada_language_server worktree is:
> 
>      "gnat"      "als main"
> 
> I could override project-name that in my projects to provide my desired
> name, and eglot will use my desired name.

Okay, that sounds good.

But let's please go back to my question: could we use the new generic in 
project-prompt-project-dir? And should we?

If we do, we'll have to default the return value to

   (abbreviate-file-name (project-root pr))

rather than your suggested

   (file-name-base (directory-file-name (project-root pr)))

. Would you say you intend to override project-name a lot? Or do you 
want to take advantage of the shorter default name in most cases?

What do you think about the first option anyway?

OTOH, it's also possible that some Powerline-style mode-line packages 
might want to use this method as well. And it seems they generally 
prefer the latter look because it's more compact. They currently don't 
show such info, though.