Support automatic installation

[michaelpj]

lsp-mode now lets clients specify download-server-fun which can be used to automatically install the server. We have static binaries so we should be able to do this. We can probably do the same thing as the vscode extension.

[michaelpj]

It looks like they may be trying to abstract out the whole provision of binaries with this lsp-dependency thing, but I'm not really sure yet.

[lukel97]

I'm taking a quick stab at this. Will report back

[michaelpj]

Quick notes on where I got to:

• Looks like we need to do our own thing, the supporting functions in lsp-mode seem quite geared towards acquiring single files.
• There are some examples of clients that do more complicated things including fetching archives:
  • https://github.com/emacs-lsp/lsp-mode/blob/master/clients/lsp-eslint.el#L296
  • https://github.com/emacs-lsp/lsp-mode/blob/master/clients/lsp-csharp.el#L145

[lukel97]

@michaelpj I was looking at the exact same files as you commented this 😃 We could do either the fancy thing that vscode-haskell does where it first downloads the wrapper, checks the version, and then downloads the corresponding GHC version binary. Or we can just download all of them including the wrapper at once. The latter will be simpler to do, but the former is nicer on disk space

[michaelpj]

I'd probably just do the latter. I think it's fine to download a reasonably chunky "distribution", especially since then it's all set up for various GHC versions. We can always be pickier later if people complain!

[lukel97]

The first scenario was not too difficult actually: The way lsp-mode.el handles finding executables and dependencies means it only really downloads what it needs. Our binaries are compressed with gzip though, so I've had to make a PR upstream to allow us to decompress them emacs-lsp/lsp-mode#2400

[lukel97]

diff --git a/lsp-haskell.el b/lsp-haskell.el
index c85b430..9ae750d 100644
--- a/lsp-haskell.el
+++ b/lsp-haskell.el
@@ -1,4 +1,4 @@
-;;; lsp-haskell.el --- Haskell support for lsp-mode
+;;; lsp-haskell.el --- Haskell support for lsp-mode -*- lexical-binding: t; -*-
 
 ;; Version: 1.0
 ;; Package-Requires: ((lsp-mode "3.0") (haskell-mode "1.0"))
@@ -246,15 +246,53 @@ and `lsp-haskell-server-args' and `lsp-haskell-server-wrapper-function'."
 ;; https://microsoft.github.io/language-server-protocol/specification#textDocumentItem
 (add-to-list 'lsp-language-id-configuration '(haskell-literate-mode . "haskell"))
 
+(defun lsp-haskell--github-system-type-suffix ()
+  (pcase system-type
+    ('gnu/linux "Linux")
+    ('windows-nt "Windows")
+    ('darwin "macOS")))
+
+(defcustom lsp-haskell-language-server-github-releases-url
+  "https://github.com/haskell/haskell-language-server/releases/latest/download/"
+  "GitHub releases url for haskell-language-server and its binaries. Make sure to include the trailing directory slash."
+  :type 'string
+  :group 'lsp-haskell
+  :package-version '(lsp-mode . "7.1"))
+
+(lsp-dependency
+ 'haskell-language-server-wrapper
+ '(:system "haskell-language-server-wrapper")
+ `(:download :url ,(concat lsp-haskell-language-server-github-releases-url
+			  (format "haskell-language-server-wrapper-%s.gz"
+				  (lsp-haskell--github-system-type-suffix)))
+	     :store-path ,(f-join lsp-server-install-dir "haskell" "haskell-language-server-wrapper")
+	     :gzip? t
+	     :set-executable? t))
+
+(defun lsp-haskell--project-ghc-version ()
+  (s-trim
+   (shell-command-to-string
+    (format "%s --project-ghc-version 2>/dev/null"
+	    (lsp-package-path 'haskell-language-server-wrapper)))))
+
 ;; Register the client itself
 (lsp-register-client
   (make-lsp--client
-    :new-connection (lsp-stdio-connection (lambda () (lsp-haskell--server-command)))
+   :new-connection (lsp-stdio-connection
+		    (lambda ()
+		      (let* ((proj-ghc-ver (lsp-haskell--project-ghc-version))
+			     (store-path (f-join lsp-server-install-dir "haskell" (format "haskell-language-server-%s" proj-ghc-ver))))
+			(message (format "proj-ghc-ver is %s\n path %s " proj-ghc-ver store-path))
+			(list
+			 (lsp-download-path
+			  :store-path store-path
+			  :set-executable? t)
+			 "--lsp"))))
     ;; Should run under haskell-mode and haskell-literate-mode. We need to list the
     ;; latter even though it's a derived mode of the former
     :major-modes '(haskell-mode haskell-literate-mode)
     ;; This is arbitrary.
-    :server-id 'lsp-haskell
+    :server-id 'haskell-language-server
     ;; We need to manually pull out the configuration section and set it. Possibly in
     ;; the future lsp-mode will asssociate servers with configuration sections more directly.
     :initialized-fn (lambda (workspace)
@@ -263,6 +301,26 @@ and `lsp-haskell-server-args' and `lsp-haskell-server-wrapper-function'."
     ;; This is somewhat irrelevant, but it is listed in lsp-language-id-configuration, so
     ;; we should set something consistent here.
     :language-id "haskell"
+    :download-server-fn (lambda (_client callback error-callback _update?)
+			  (lsp-package-ensure
+			   'haskell-language-server-wrapper
+			   (lambda ()
+			     (let*
+				 ((proj-ghc-ver (lsp-haskell--project-ghc-version))
+				  (binary-store-path
+				   (f-join lsp-server-install-dir "haskell" (format "haskell-language-server-%s" proj-ghc-ver))))
+			       (lsp-download-install
+				callback
+				error-callback
+				:url (concat
+				      lsp-haskell-language-server-github-releases-url
+				      (format
+				       "haskell-language-server-%s-%s.gz"
+				       (lsp-haskell--github-system-type-suffix)
+				       proj-ghc-ver))
+				:store-path binary-store-path
+				:gzip? t)))
+			   error-callback))
     ))
 
 ;; ---------------------------------------------------------------------

Here's my POC though with this upstream patch: https://streamable.com/d7se3g

[alanz]

@bubba looks great

[jcs090218]

Any progress on this?

[michaelpj]

Nope. If someone wants to pick this up now, I'd highly recommend delegating to ghcup for installation, that's what the vscode extension does.