Add purescript formatting support (#14984)

CHANGELOG.develop

@@ -3130,6 +3130,7 @@ files (thanks to Daniel Nicolai)
 - Enabled =purescript-decl-scan-mode= when loading =purescript-mode=
   (thanks to Bjarke Vad Andersen)
 - Allow adding node_modules/.bin path to exec-path (thanks to Anupam Jain)
+- Added support for purescript formatters (thanks to Anupam Jain)
 - Improved purescript keybinding discoverability & ergonomics.
   (thanks to Jason Walker)
 - Added =purescript-mode= to =spacemacs-indent-sensitive-modes=

layers/+lang/purescript/README.org

@@ -9,6 +9,7 @@
   - [[#features][Features:]]
 - [[#install][Install]]
 - [[#configuration][Configuration]]
+  - [[#formatting][Formatting]]
   - [[#add-import-on-completion][Add import on completion]]
   - [[#node-modules][Node Modules]]
   - [[#error-popup][Error popup]]
@@ -17,6 +18,7 @@
   - [[#purescript][Purescript]]
     - [[#imports][Imports]]
     - [[#psc-ide][psc-ide]]
+    - [[#formatting-1][Formatting]]
   - [[#repl][REPL]]
 
 * Description
@@ -39,6 +41,33 @@ binaries (psc-ide-server, psci,...) are on your path. Installation instructions
 can be found [[https://github.com/purescript/documentation/blob/master/guides/Getting-Started.md][here]].
 
 * Configuration
+  
+** Formatting
+   
+The following formatting tools are currently supported:
+- =purs-tidy= (default): [https://github.com/natefaubion/purescript-tidy][Purs-tidy]]
+
+You can choose the formatting tool by setting =purescript-fmt-tool=
+variable in your =purescript= config section:
+
+#+BEGIN_SRC elisp
+  (setq-default dotspacemacs-configuration-layers '(
+    (purescript :variables
+                purescript-fmt-tool 'purs-tidy)))
+#+END_SRC
+
+You can run the formatter manually with either `M-x spacemacs/purescript-format`
+or with the shortcut `SPC m =`.
+
+To enable automatic formatting of the buffer on save, enable =purescript-fmt-on-save=
+variable in your =purescript= config section:
+
+#+BEGIN_SRC elisp
+  (setq-default dotspacemacs-configuration-layers '(
+    (purescript :variables
+                purescript-fmt-on-save t)))
+#+END_SRC
+
 ** Add import on completion
 Set =purescript-add-import-on-completion= to nil to make =psc-ide= stop adding
 imports on completion. Default value is =t=.
@@ -113,6 +142,12 @@ intellisense config for LSP.
 | ~SPC m h t~   | Show type at point                                                        |
 | ~SPC m g g~   | Goto definition for identifier at point                                   |
 
+*** Formatting
+
+| Key binding   | Description                                                               |
+|---------------+---------------------------------------------------------------------------|
+| ~SPC m =~     | Format the buffer                                                         |
+
 ** REPL
 [[https://github.com/ardumont/emacs-psci][psci]] provides a very basic REPL for purescript. The following key
 bindings are available:

layers/+lang/purescript/config.el

@@ -25,6 +25,13 @@
 
 (spacemacs|define-jump-handlers purescript-mode)
 
+(defvar purescript-fmt-on-save nil
+  "Run formatter on buffer save.")
+
+(defvar purescript-fmt-tool 'purs-tidy
+  "The name of the tool to be used for Purescript source code formatting.
+Possible values are 'purs-tidy (default).")
+
 (defvar purescript-add-import-on-completion t
   "If non-nil adds imports for completed identifiers")
 

layers/+lang/purescript/funcs.el

@@ -37,3 +37,44 @@
      (spacemacs|add-company-backends
        :backends company-psc-ide-backend
        :modes purescript-mode))))
+
+(defun spacemacs/purescript-format ()
+  "Call formatting tool specified in `purescript-fmt-tool'."
+  (interactive)
+  (call-interactively
+   (pcase purescript-fmt-tool
+     ('purs-tidy 'spacemacs/purescript-purs-tidy-format-buffer)
+     (_ (user-error
+         "%s isn't a valid purescript formatter. Possible values are 'purs-tidy"
+         purescript-fmt-tool)))))
+
+(defun spacemacs/purescript-purs-tidy-format-buffer ()
+  "Format buffer with purs-tidy."
+  (interactive)
+  (if (executable-find "purs-tidy")
+      (let*  ((extension (file-name-extension (or buffer-file-name "tmp.purs") t))
+              (tmpfile (make-temp-file "~fmt-tmp" nil extension))
+              (coding-system-for-read 'utf-8)
+              (coding-system-for-write 'utf-8)
+              (outputbuf (get-buffer-create "*~fmt-tmp.purs*")))
+        (unwind-protect
+            (progn
+              (with-current-buffer outputbuf (erase-buffer))
+              (write-region nil nil tmpfile)
+              (if (zerop (apply #'call-process-region nil nil "purs-tidy" nil
+                                `(,outputbuf ,tmpfile) nil
+                                `("format")))
+                  (let ((p (point)))
+                    (save-excursion
+                      (with-current-buffer (current-buffer)
+                        (replace-buffer-contents outputbuf)))
+                    (goto-char p)
+                    (message "formatted.")
+                    (kill-buffer outputbuf))
+                (message "Formatting failed!")
+                (display-buffer outputbuf)))
+            (delete-file tmpfile)))
+    (error "purs-tidy not found. Run \"npm install -g purs-tidy\"")))
+
+(defun spacemacs/purescript-fmt-before-save-hook ()
+  (add-hook 'before-save-hook 'spacemacs/purescript-format t t))

layers/+lang/purescript/packages.el

@@ -50,14 +50,16 @@
       (add-hook 'purescript-mode-hook 'turn-on-purescript-indentation)
       (add-hook 'purescript-mode-hook 'purescript-decl-scan-mode)
       (add-hook 'purescript-mode-hook #'spacemacs//purescript-setup-backend)
+      (when purescript-fmt-on-save
+        (add-hook 'purescript-mode-hook 'spacemacs/purescript-fmt-before-save-hook))
       (spacemacs/declare-prefix-for-mode 'purescript-mode "mg" "goto")
       (spacemacs/declare-prefix-for-mode 'purescript-mode "mi" "imports")
       (spacemacs/set-leader-keys-for-major-mode 'purescript-mode
         "i="  'purescript-mode-format-imports
         "i`"  'purescript-navigate-imports-return
         "ia"  'purescript-align-imports
-        "in"  'purescript-navigate-imports))))
-
+        "in"  'purescript-navigate-imports
+        "=" 'spacemacs/purescript-format))))
 
 (defun purescript/init-psci ()
   (use-package psci