Extending built-in python methods by prefixing eglot-alternatives

[hexmode]

I want to add my poetry-enabled pylsp method for poetry projects while still falling back to the built-in eglot-alternatives.

I think this works, but is there a better way?

 (let ((replaceme (alist-get '(python-mode python-ts-mode) eglot-server-programs nil nil #'equal)))
		 (setf replaceme `(eglot-alternatives (list '("poetry" "run" "pylsp") replaceme))))

[joaotavora]

I think this works,

I think this doesn't work: you're just making a new cons and eglot-server-programs won't know about it. If you know how to use setf give it some "place" so you can actually mutate e-s-programs. There are many Lisp list-mutating tutorials around (and with some trial and error you'll find it).

[hexmode]

I'm not sure what to do with this bit that describe-variable says is the entry for (python-mode python-ts-mode) in e-s-programs:

 ((python-mode python-ts-mode) . #f(compiled-function (&optional interactive project) #<bytecode 0x1f38db1f384f2543>))

[hexmode]

I've been messing around with this and come up with the following that seems to almost work:

(defun eglot-prepend-server (mode-key new-server)
  "Prepend a NEW-SERVER choice to MODE-KEY for `eglot-server-programs` and use the original setting as fallback."
  (let* ((original-function (alist-get mode-key eglot-server-programs nil nil #'equal)))
    ;; Check if there's a valid function already in place
    (if (functionp original-function)
        (setf (alist-get mode-key eglot-server-programs nil nil #'equal)
              (lambda (&optional interactive project)
                ;; Attempt to find 'new-server' first
                (let ((try-first (and (executable-find (car new-server))
                                      (cons (executable-find (car new-server)) (cdr new-server)))))
                  (if try-first
                      (cons try-first (if interactive '() nil))  ; If found and not interactive, use it. '()' for arguments template.
                      (funcall original-function interactive project))))) ; Fallback to original function
      (error "No valid server-choosing function for %s" (prin1-to-string mode-key)))))

Usage

(eglot-prepend-server '(python-mode python-ts-mode) '("poetry" "run" "pylsp"))

I say "almost" but the backtrace looks like

Debugger entered--Lisp error: (wrong-type-argument processp nil)
  process-put(nil jsonrpc-stderr #<buffer  *EGLOT (jenkins-inventory/(python-mode python-ts-mode)) stderr*>)
  #f(compiled-function (conn slots) #<bytecode 0xedbd9741fc110c4>)(#<eglot-lsp-server eglot-lsp-server-10ec86abe06e> (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown))
  apply(#f(compiled-function (conn slots) #<bytecode 0xedbd9741fc110c4>) (#<eglot-lsp-server eglot-lsp-server-10ec86abe06e> (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown)))
  #f(compiled-function (&rest args) #<bytecode -0x10f10a0df0dc0cf4>)(#<eglot-lsp-server eglot-lsp-server-10ec86abe06e> (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown))
  apply(#f(compiled-function (&rest args) #<bytecode -0x10f10a0df0dc0cf4>) #<eglot-lsp-server eglot-lsp-server-10ec86abe06e> (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown))
  initialize-instance(#<eglot-lsp-server eglot-lsp-server-10ec86abe06e> (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown))
  #f(compiled-function (class &rest slots) "Default constructor for CLASS `eieio-default-superclass'.\nSLOTS are the initialization slots used by `initialize-instance'.\nThis static method is called when an object is constructed.\nIt allocates the vector used to represent an EIEIO object, and then\ncalls `initialize-instance' on that object." #<bytecode -0x18d0d8debe007ca5>)(eglot-lsp-server :name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown)
  apply(#f(compiled-function (class &rest slots) "Default constructor for CLASS `eieio-default-superclass'.\nSLOTS are the initialization slots used by `initialize-instance'.\nThis static method is called when an object is constructed.\nIt allocates the vector used to represent an EIEIO object, and then\ncalls `initialize-instance' on that object." #<bytecode -0x18d0d8debe007ca5>) eglot-lsp-server (:name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown))
  make-instance(eglot-lsp-server :name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown)
  apply(make-instance eglot-lsp-server :name "EGLOT (jenkins-inventory/(python-mode python-ts-mode))" :events-buffer-config (:size 2000000 :format full) :notification-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b95589798aa>) :request-dispatcher #f(compiled-function (server method params) #<bytecode 0x1f130b957a9798aa>) :on-shutdown eglot--on-shutdown nil)
  eglot--connect((python-mode python-ts-mode) (vc Git "~/work/connectify/jenkins-inventory/") eglot-lsp-server (("/home/mah/.asdf/shims/poetry" "run" "pylsp")) ("python" "python"))
  eglot((python-mode python-ts-mode) (vc Git "~/work/connectify/jenkins-inventory/") eglot-lsp-server (("/home/mah/.asdf/shims/poetry" "run" "pylsp")) ("python" "python") t)
  funcall-interactively(eglot (python-mode python-ts-mode) (vc Git "~/work/connectify/jenkins-inventory/") eglot-lsp-server (("/home/mah/.asdf/shims/poetry" "run" "pylsp")) ("python" "python") t)

I'm taking a break for now and might return later. in any case, I leave what i have now in case it is of any use to others.

[joaotavora]

In the default association list, the value for the key which is the 2-element list (python-mode python-ts-mode) is a function. That's what this is telling you:

#1432 (reply in thread)

It looks like a list when you look at the source code, because Lisp source code all looks like a list. But the object in memory is a (compiled) function and you can't just mutate it. But you can:

(setcdr (cl-find 'python-mode eglot-server-programs
                 :key (lambda (a) (ensure-list (car a)))
                 :test #'memq)
        42)

of course 42 isn't a very useful LSP server, so try:

(setcdr (cl-find 'python-mode eglot-server-programs
                 :key (lambda (a) (ensure-list (car a)))
                 :test #'memq)
        (eglot-alternatives '("alternative1" "alternative2")))

You can use (setf (cdr instead of setcdr of course. And you can use alist-get instead of cl-find. You can do whatever. The polymorphic structure of eglot-server-programs (which has a bad case of featuritis of the backward-compatible kind) makes this manipulation hard, but possible. In fact, reading your function, it seems you've come this far, more or less. I would leverage assoc in your prepend-server to avoid repeting the alist-get twice. Also trace-values could be useful for debugging.

If you're enjoying this,feel free to continue. Good luck! Personally I'd just copy paste the interesting servers and stick a new entry on top of eglot-server-programs with just the servers I'm interested in.

[hexmode]

Thanks for this!

The following worked for me:

  (setcdr (cl-find 'python-mode eglot-server-programs
            :key (lambda (a) (ensure-list (car a)))
            :test #'memq)
    (eglot-alternatives '(("poetry" "run" "pylsp"))))