Highlight and remove extraneous whitespace in emacs (Shallow Thoughts)

Highlight and remove extraneous whitespace in emacs

I recently got annoyed with all the trailing whitespace I saw in files edited by Windows and Mac users, and in code snippets pasted from sites like StackOverflow. I already had my emacs set up to indent with only spaces:

(setq-default indent-tabs-mode nil)
(setq tabify nil)

and I knew about M-x delete-trailing-whitespace ... but after seeing someone else who had an editor set up to show trailing spaces, and tabs that ought to be spaces, I wanted that too.

To show trailing spaces is easy, but it took me some digging to find a way to control the color emacs used:

;; Highlight trailing whitespace.
(setq-default show-trailing-whitespace t)
(set-face-background 'trailing-whitespace "yellow")

I also wanted to show tabs, since code indented with a mixture of tabs and spaces, especially if it's Python, can cause problems. That was a little harder, but I eventually found it on the EmacsWiki: Show whitespace:

;; Also show tabs.
(defface extra-whitespace-face
  '((t (:background "pale green")))
  "Color for tabs and such.")

(defvar bad-whitespace
  '(("\t" . 'extra-whitespace-face)))

While I was figuring this out, I got some useful advice related to emacs faces on the #emacs IRC channel: if you want to know why something is displayed in a particular color, put the cursor on it and type C-u C-x = (the command what-cursor-position with a prefix argument), which displays lots of information about whatever's under the cursor, including its current face.

Once I had my colors set up, I found that a surprising number of files I'd edited with vim had trailing whitespace. I would have expected vim to be better behaved than that! But it turns out that to eliminate trailing whitespace, you have to program it yourself. For instance, here are some recipes to Remove unwanted spaces automatically with vim.

Tags: editors, emacs
[ 16:41 Feb 18, 2017    More linux/editors | permalink to this entry | ]