Subject: bug#58790: Eglot URI parsing bug when using clojure-lsp server

From: João Távora <[email-masked]>
Date: Sat, 29 Oct 2022 03:02:56 +0100

Dmitry Gutov <[email-masked]> writes:

> We don't provide a setter for 'project-root', so I don't understand
> the expectation of being able to modify project-external-roots for an
> arbitrary project type either.

I think I understand your confusion.  I'm not suggesting that Eglot
modifies it.  I'll explain better below.

>>> Dmitry: Or create an Eglot-specific project backend.
>> I don't understand this suggestion either.  Normally Eglot is a
>> client
>> of project information maintained by other project.el backends.  Very
>> commonly VC projects, but not always necessarily so.  That clashes with
>> the idea of making Eglot simultaneously a supplier of this information.
>
> There is indeed certain tension, but if Eglot wants to decide stuff
> about the project (which, as I said in the past, could be a reasonable
> idea), then it could provide its own project backend. We're not
> necessarily at that point, though, because...

Eglot doesn't want to decide anything about project. Eglot justs wants
to go into user visible projects and answer the question:
(project-current).  It wants this because it maps project/major-mode
pairs to server connections. 

Eglot doesn't care if the project is of type 'vc, 'transient,
'visual-studio-solution-file, 'joes-complicated-project, etc.  

So Eglot providing a project backend doesn't make sense.  Maybe you
think I'm suggesting that Eglot that could collect these references to
jars coming from the LSP server and add them to project-external-roots
somehow.  I'm not suggesting that.  

It's just that an arbitrary project backend, other than 'vc or
'transient, could add a method to project-external-roots.  That would be
the user's job.  I suppose Clojure packages declare somewhere which jars
they use.  They probably store this information in a file.  Java used
some ghastly .xml Ant file or Maven or whatever.  A specialized project
backend could read the file and use it in an implementation of
project-external-roots.  At this this is how I interpret project.el's
CLOS-like protocol for defining new project backends.

>> Please read the summary of the outlined above.  Maybe there's nothing to
>> be done in project.el if eglot-extend-to-xref is to be used.
>
> ...indeed you could stop at that.

Maybe.  eglot-extend-to-xref works very well for non-jars, at least for
C++ and clangd.  Subsequent M-. work very well, too.

The downside is that once a system file discovered by the LSP server, it
is associated with a given server (_not project_) in Eglot.  I don't
know what happens if another server also points to the same file.
Probably nothing very bad, but there may be some suprising behavior: I
haven't tested.

> Having the jars in project-external-roots could enable the users
> (after certain integration work) to search across their contents with
> project-or-external-find-regexp, or jump to files inside with
> project-or-external-find-file.

That's a very nice point.  I don't use Java fortunately, but when I did
a long time ago, I think I remember Eclipse let me do this.

> But as for xref-find-definitions, item 4 in your list should be enough
> (with either of the alternatives as underlying implementation).

Let's see what Danny says.

João