Added support for Microsoft Python Language Server

<<26/04/2019>>
Incorporated feedback from robbyoconnor and yyoncho.
Rebased.

<<08/04/2019>>
Rebased on develop tip

<<17/04/2019>>
Rebased

<<02/06/2019>>
Rebased. Incorporated feedback from duianto.

CHANGELOG.develop

@@ -2045,7 +2045,11 @@ Other:
 - Use =python-mode= for SCons script files (thanks to shanemikel)
 - Added LSP support, which can be used by enabling the =lsp= layer and setting
   the =python= layer's =python-backend= variable to =lsp=
-  (thanks to Yuan Fu and Sylvain Benner)
+  (thanks to Yuan Fu and Sylvain Benner).
+- The LSP backend can use either the =pyls= (default) server or the =mspyls=
+  (Microsoft) implementation, which may be selected by setting the
+  =python-lsp-server= layer variable to =mspyls=
+  (thanks to Cormac Cannon).
 - Added ~SPC m t l~ key binding to re-run the last test command
   (thanks to Benoit Coste).
 - Added support for breakpoints for the =trepan3k= python debugger

layers/+lang/python/README.org

@@ -13,6 +13,8 @@
 - [[#backends][Backends]]
   - [[#anaconda][Anaconda]]
   - [[#language-server-protocol][Language Server Protocol]]
+    - [[#python-language-server][python-language-server]]
+    - [[#microsoft-python-language-server][Microsoft python language server]]
 - [[#additional-tools][Additional tools]]
   - [[#syntax-checking][Syntax checking]]
   - [[#test-runner][Test runner]]
@@ -46,7 +48,9 @@ This layer adds support for the Python language.
 ** Features:
 - Support for the following backends:
   - [[https://github.com/proofit404/anaconda-mode][anaconda]] (default),
-  - [[https://github.com/emacs-lsp/lsp-python][Language Server Protocol]] (experimental),
+  - [[https://github.com/emacs-lsp/lsp-python][Language Server Protocol]] (experimental - 2 implementations),
+    - python-language-server
+    - Microsoft python language server
 - Auto-completion
 - Code Navigation
 - Documentation Lookup using [[https://github.com/proofit404/anaconda-mode][anaconda-mode]] and [[https://github.com/tsgates/pylookup][pylookup]]
@@ -87,6 +91,14 @@ Backend can be chosen on a per project basis using directory local variables
 
 *Note:* you can easily add a directory local variable with ~SPC f v d~.
 
+The available options are:
+
+| symbol    | description                      |
+|-----------+----------------------------------|
+| 'anaconda | Default                          |
+| 'lsp      | python-language-server package   |
+| 'lsp-ms   | Microsoft python language server |
+
 * Backends
 ** Anaconda
 =anaconda-mode= tries to install the dependencies itself but sometimes
@@ -113,6 +125,22 @@ setting your =PYTHONPATH= as explained at
 [[https://github.com/proofit404/anaconda-mode#pythonpath]]
 
 ** Language Server Protocol
+
+The =lsp= backend can use either of the following language server implementations:
+
+| symbol  | description                              |
+|---------+------------------------------------------|
+| 'pyls   | python-language-server package (default) |
+| 'mspyls | Microsoft python language server         |
+
+=pyls= is used by default - to use the Microsoft server, set the =python-lsp-server=
+layer variable as follows:
+
+#+BEGIN_SRC elisp
+  (python :variables python-backend 'lsp python-lsp-server 'mspyls)
+#+END_SRC
+
+*** python-language-server
 You just have to install python language server package:
 
 #+BEGIN_SRC sh
@@ -133,6 +161,32 @@ dependencies in a pipenv environment, you'll want to set the ~python-pipenv-acti
 config variable to ~t~. This activates your pipenv before enabling the
 lsp backend.
 
+*** Microsoft python language server
+Paraphrasing the instructions provided by the author of the =lsp-python-ms= package:
+
+#+BEGIN_SRC sh
+  git clone https://github.com/Microsoft/python-language-server.git
+  cd python-language-server/src/LanguageServer/Impl
+  dotnet build -c Release
+  dotnet publish -c Release -r <RUNTIME>
+#+END_SRC
+
+where ~<RUNTIME>~ is one of the [[https://docs.microsoft.com/en-us/dotnet/core/rid-catalog][runtime IDs supported by dotnet core]]. One of ~linux-x64~, ~osx-x64~, ~win10-x64~ should
+cover most use cases.
+
+The default package configuration assumes the executable is located in a folder included in your system path.
+To use the latest built version in a cloned git repo, use the ~python-lsp-git-root~ config variable, e.g.:
+
+#+BEGIN_SRC elisp
+  (setq-default dotspacemacs-configuration-layers
+    '((python :variables
+              python-backend 'lsp-ms
+              python-lsp-git-root "~/dev/python/python-language-server")))
+#+END_SRC
+
+N.B. If you're using Arch linux or a derivative distribution, you can install the =microsoft-python-language-server=
+package from the AUR.
+
 * Additional tools
 ** Syntax checking
 Syntax checking uses =flake8= package:

layers/+lang/python/config.el

@@ -18,6 +18,13 @@
   "The backend to use for IDE features. Possible values are `anaconda'
 and `lsp'.")
 
+(defvar python-lsp-server 'pyls
+  "Language server to use for lsp backend. Possible values are `pyls'
+and `mspyls'")
+
+(defvar python-lsp-git-root nil
+  "If non-nil, use a development version of the language server in this folder")
+
 (defvar python-pipenv-activate nil
   "If non-nil, activate pipenv before enabling backend")
 

layers/+lang/python/funcs.el

@@ -18,16 +18,15 @@
 
 (defun spacemacs//python-setup-company ()
   "Conditionally setup company based on backend."
-  (pcase python-backend
-    (`anaconda (spacemacs//python-setup-anaconda-company))
-    (`lsp (spacemacs//python-setup-lsp-company))))
+  (if (eq python-backend `anaconda)
+    (spacemacs//python-setup-anaconda-company)
+    (spacemacs//python-setup-lsp-company)))
 
 (defun spacemacs//python-setup-eldoc ()
   "Conditionally setup eldoc based on backend."
   (pcase python-backend
     ;; lsp setup eldoc on its own
-    (`anaconda (spacemacs//python-setup-anaconda-eldoc))))
-
+    (spacemacs//python-setup-anaconda-eldoc)))
 
 ;; anaconda
 
@@ -89,8 +88,8 @@
 (defun spacemacs//python-default ()
   "Defaut settings for python buffers"
   (setq mode-name "Python"
-        tab-width python-tab-width
-        fill-column python-fill-column)
+    tab-width python-tab-width
+    fill-column python-fill-column)
 
   ;; since we changed the tab-width we need to manually call python-indent-guess-indent-offset here
   (when python-spacemacs-indent-guess
@@ -187,10 +186,10 @@ as the pyenv version then also return nil. This works around https://github.com/
   "autoflake --remove-all-unused-imports -i unused_imports.py"
   (interactive)
   (if (executable-find "autoflake")
-      (progn
-        (shell-command (format "autoflake --remove-all-unused-imports -i %s"
-                               (shell-quote-argument (buffer-file-name))))
-        (revert-buffer t t t))
+    (progn
+      (shell-command (format "autoflake --remove-all-unused-imports -i %s"
+                       (shell-quote-argument (buffer-file-name))))
+      (revert-buffer t t t))
     (message "Error: Cannot find autoflake executable.")))
 
 (defun spacemacs//pyenv-mode-set-local-version ()

layers/+lang/python/packages.el

@@ -43,6 +43,8 @@
         ;; packages for anaconda backend
         anaconda-mode
         (company-anaconda :requires company)
+        ;; packages for Microsoft LSP backend
+        (lsp-python-ms :requires lsp-mode)
         ))
 
 (defun python/init-anaconda-mode ()
@@ -420,3 +422,18 @@ fix this issue."
                  (eq 'yapf python-formatter))
         (add-hook 'python-mode-hook 'yapf-mode)))
     :config (spacemacs|hide-lighter yapf-mode)))
+
+(defun python/init-lsp-python-ms ()
+  (use-package lsp-python-ms
+    :if (eq python-lsp-server 'mspyls)
+    :ensure nil
+    :config
+
+    (if python-lsp-git-root
+      ;; Use dev version of language server checked out from github
+      (progn
+        (setq lsp-python-ms-dir
+          (expand-file-name (concat python-lsp-git-root "/output/bin/Release/")))
+        (message "lsp-python-ms: Using version at `%s'" lsp-python-ms-dir))
+      ;; Use a precompiled exe
+      (setq lsp-python-ms-executable "Microsoft.Python.LanguageServer"))))