Use ws-butler

At work I have to work with a lot of files that other people work on as well.
Other people don’t usually have their editor set up to remove all trailing
whitespace, and we’re not allowed to make a change that includes a lot of extra
whitespace changes[1]. So I end up having to revert a lot of whitespace changes
just before submitting. And if I then have to make more changes, for example
because something was pointed out in a code review, I have to do it again.

‘ws-butler’ promises that it will still prevent me from submitting extraneous
whitespace, but will not touch lines that I haven’t changed, so that would
prevent me from having to revert them all the time.

[1]: This is good, having a lot of whitespace changes can distract from or even
completely hide the actual change you’re trying to make.

oni-core.el

@@ -4,8 +4,8 @@
 
 ;; Author: Tom Willemse <tom@ryuslash.org>
 ;; Keywords: local
-;; Version: 2020.1015.100916
-;; Package-Requires: (oni-data-dir expand-region multiple-cursors embrace gcmh diminish)
+;; Version: 2020.1015.102640
+;; Package-Requires: (oni-data-dir expand-region multiple-cursors embrace gcmh diminish ws-butler)
 
 ;; This program is free software; you can redistribute it and/or modify
 ;; it under the terms of the GNU General Public License as published by
@@ -31,6 +31,7 @@
 (require 'gcmh)
 (require 'oni-data-dir)
 (require 'recentf)
+(require 'ws-butler)
 
 (defconst oni-core--auto-save-directory (oni-data-dir-locate "auto-save-files/")
   "Directory where auto-saves go.")
@@ -40,11 +41,6 @@
 (defvar oni-core--recentf-idle-timer nil
   "Internal variable keeping track of a timer started for ‘recentf-save-list’.")
 
-(defun oni-core--destroy-trailing-whitespace ()
-  "Delete trailing whitespace everywhere, except in Markdown buffers."
-  (if (not (eq major-mode 'markdown-mode))
-      (delete-trailing-whitespace)))
-
 (defun oni-core--switch-newline-keys ()
   "Switch the ‘C-j’ and ‘RET’ keys in the local buffer."
   (if electric-indent-mode
@@ -131,7 +127,6 @@
 (setq-default truncate-lines t)
 (setq-default fill-column 80)
 
-(add-hook 'before-save-hook #'oni-core--destroy-trailing-whitespace)
 (add-hook 'before-save-hook 'time-stamp)
 (add-hook 'electric-indent-local-mode-hook #'oni-core--switch-newline-keys)
 (add-hook 'minibuffer-setup-hook 'electric-pair-local-mode)
@@ -155,11 +150,13 @@
         (run-with-idle-timer 10 t #'oni-core-recentf-save-list-silently)))
 
 (diminish 'gcmh-mode)
+(diminish 'ws-butler-mode)
 
 (electric-indent-mode -1)
 (winner-mode)
 (recentf-mode)
 (gcmh-mode)
+(ws-butler-global-mode)
 
 (add-to-list 'display-buffer-alist
              `(,(rx string-start

test/integration/oni-core.bats

@@ -35,3 +35,21 @@
 
     [[ "$output" == *"t" ]]
 }
+
+@test "Starting Emacs diminishes ws-butler-global-mode" {
+    run emacs -batch -l package -f package-initialize -l subr-x \
+        -eval "(prin1 (string-empty-p (car (alist-get 'ws-butler-mode minor-mode-alist))))"
+
+    echo "$output"
+
+    [[ "$output" == *"t" ]]
+}
+
+@test "Starting Emacs turns on ws-butler-mode" {
+    run emacs -batch -l package -f package-initialize \
+        -eval "(prin1 (bound-and-true-p ws-butler-mode))"
+
+    echo "$output"
+
+    [[ "$output" == *"t" ]]
+}