Re: Eglot, project.el, and python virtual environments

[Eric Abrahamsen]

Danny Freeman <danny@dfreeman.email> writes:

> Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>
>> > > project_root
>> > > ├── .git
>> > > ├── src
>> > > │   └── python
>> > > │       ├── VeryImportantLambda
>> > > │       │   └── .venv
>> > > │       ├── MoreImportance
>> > > │       │   └── .venv
>> > > │       ├── RunInCaseOfEmergency
>> > > │       │   └── .venv
>
> I just realized you posted information about the .venv files in your
> original post and I completely overlooked that lol. 
>
>> Thank you very much, that does help indeed! I started off down this path
>> and had gotten as far as eglot-lsp-context. Then I realized I couldn't
>> just return a directory, it had to be a project object, and that's when
>> I decided someone else must have a better approach. But it's great to
>> see all this laid out, and knowing about `(cons 'transient root)' is
>> very helpful, as well.
>>
>> I'll play around with this a bit. It seems like a not-outlandish
>> situation, and I wonder if it might not be useful to provide some
>> standardized method of helping Eglot find an alternate project.
>>
>> Thanks again,
>> Eric
>
> Anyways yeah, I think I've heard about someone else running into this as
> well. Maybe it was on the reddit emacs forum. Either way, I do not think
> you are the first.
>
> What might an extension for Eglot look like? Maybe a built in
> `project-find-functions' implementation that does something similar
> looking for a `.eglot-lsp-root` (or probably something configurable) as
> a transient project root? I don't know if that would cause problems out
> of the box for some people, but it seems safe.

That was my first thought: a file cookie that told Eglot to consider
this directory a project root.

But I don't know enough about Eglot and its internals to be sure. I'm
not even really sure what Eglot uses a project definition for: I guess
to decide which buffers in a given major-mode should use the same
invocation of a language server protocol? One process used in all those
project buffers? Is that even how it groups things? I don't know.

The core issue in my case is that I need to be able to tell Eglot to use
a separate language server executable for all python-mode buffers within
a certain directory tree. Maybe there is a simpler way of doing that
that doesn't require me to trick Eglot into thinking the project is
smaller than it is. All a virtual environment does, fundamentally, is
munge PATH so that Python-related executables are found locally, rather
than system-wide. Maybe there's a relatively simple way to explicitly
tell Eglot to do that.

I think the approach I'm on now can probably be made to work, but it
would be nice to know if there's a simpler way. I might spend a bit of
time looking at Eglot's source, and open a bug report.

Thanks!
Eric