bug#72088: eglot: Segregates language servers in a way that hampers polyglot language servers

[Niels Thykier <niels@thykier.net>]

Niels Thykier:
> João Távora:
>> On Sun, Jul 14, 2024, 05:37 Eli Zaretskii <eliz@gnu.org> wrote:
>>
>>> AFAIU, the OP tried to use the same LSP server for several languages,
>>> or something like that.
>>>
>>
>> Yes, but how? What are the major modes in question? What information was
>> added to eglot-server-programs, if any?
> Hi,
> 
> The `eglot-server-programs` are defined as:
> 
> ```
> (with-eval-after-load 'eglot
>      (add-to-list 'eglot-server-programs
>              '(debian-control-mode . ("debputy" "lsp" "server")))
>      (add-to-list 'eglot-server-programs
>              '(debian-changelog-mode . ("debputy" "lsp" "server")))
>      (add-to-list 'eglot-server-programs
>              '(debian-copyright-mode . ("debputy" "lsp" "server")))
>      (add-to-list 'eglot-server-programs
>              '(makefile-gmake-mode . ("debputy" "lsp" "server")))
>      (add-to-list 'eglot-server-programs
>              '(yaml-mode . ("debputy" "lsp" "server")))
>      (add-to-list 'eglot-server-programs
>              '(debian-autopkgtest-control-mode . ("debputy" "lsp" 
> "server")))
> )
> ```
> 
> [...]
> 
> I read through 
> https://www.gnu.org/software/emacs/manual/html_node/eglot/Setting-Up-LSP-Servers.html and I do not see anything here that decides how to control whether one or two instances per project will be spawned.
> 
> Best regards,
> Niels
> 

No, I think I see it now.

I think I have overlooked this paragraph:

"""
The major-mode of the alist elements can be either a symbol of an Emacs 
major mode or a list of the form (mode :language-id id), with mode being 
a major-mode symbol and id a string that identifies the language to the 
server (if Eglot cannot by itself convert the major-mode to the language 
identifier string required by the server). In addition, major-mode can 
be a list of several major modes specified in one of the above forms – 
this means a running instance of the associated server is responsible 
for files of multiple major modes or languages in the project.
"""

I will retry with this in mind and see if that solves the problem. If it 
does, I will close this bug.

Best regards,
Niels