Replace delete-trailing-whitespace with ws-butler

ws-butler only strips trailing spaces on lines that have been modified.

+ ws-butler is disabled if editorconfig enables
  trim_trailing_whitespace, which resorts to delete-trailing-whitespace
  instead.
+ Updates doom|(enable|disable)-delete-trailing-whitespace hooks to use
  ws-butler-mode.

core/autoload/editor.el

@@ -283,12 +283,12 @@ with weak native support."
 (defun doom|enable-delete-trailing-whitespace ()
   "Enables the automatic deletion of trailing whitespaces upon file save.
 
-i.e. adds `delete-trailing-whitespace' to `write-file-functions', buffer-locally."
+i.e. enables `ws-butler-mode' in the current buffer."
-  (add-hook 'write-file-functions #'delete-trailing-whitespace nil t))
+  (ws-butler-mode +1))
 
 ;;;###autoload
 (defun doom|disable-delete-trailing-whitespace ()
   "Disables the automatic deletion of trailing whitespaces upon file save.
 
-i.e. removes  `delete-trailing-whitespace' from `write-file-functions'."
+i.e. disables `ws-butler-mode' in the current buffer."
-  (remove-hook 'write-file-functions #'delete-trailing-whitespace t))
+  (ws-butler-mode -1))

core/core-editor.el

@@ -81,11 +81,6 @@ fundamental-mode) for performance sake."
 
 (add-hook 'after-save-hook #'executable-make-buffer-file-executable-if-script-p)
 
-;; Deleting trailing whitespace is on by default, but must be set on
-;; write-file-functions, so that editorconfig can see it (so it doesn't add it
-;; redundantly and can remove it when needed).
-(add-hook 'write-file-functions #'delete-trailing-whitespace)
-
 ;; revert buffers for changed files
 (def-package! autorevert
   :after-call after-find-file
@@ -300,5 +295,12 @@ savehist file."
   [remap describe-variable] #'helpful-variable
   [remap describe-key]      #'helpful-key)
 
+;; `ws-butler' --- a better `delete-trailing-whitespaces'
+(def-package! ws-butler
+  :after-call (after-find-file) 
+  :config
+  (nconc ws-butler-global-exempt-modes '(special-mode comint-mode term-mode eshell-mode))
+  (ws-butler-global-mode))
+
 (provide 'core-editor)
 ;;; core-editor.el ends here

core/packages.el

@@ -32,6 +32,7 @@
 (package! pcre2el)
 (package! smartparens)
 (package! undo-tree)
+(package! ws-butler)
 
 ;; core-projects.el
 (package! projectile)

modules/tools/editorconfig/config.el

@@ -42,7 +42,15 @@ extension, try to guess one."
       (apply orig-fn args)))
   (advice-add #'editorconfig-call-editorconfig-exec :around #'doom*editorconfig-smart-detection)
 
+  (defun +editorconfig|disable-ws-butler-maybe (props)
+    "Disable `ws-butler-mode' if trim_trailing_whitespace is true."
+    (when (equal (gethash 'trim_trailing_whitespace props) "true")
+      (ws-butler-mode -1)))
+  (add-hook 'editorconfig-custom-hooks #'+editorconfig|disable-ws-butler-maybe)
+
   (defun +editorconfig|disable-indent-detection (props)
+    "Inhibit `dtrt-indent' if an explicit indent_style and indent_size is
+specified by editorconfig."
     (when (or (gethash 'indent_style props)
               (gethash 'indent_size props))
       (setq doom-inhibit-indent-detection t)))