This Emacs library minor mode will intelligently call whitespace-cleanup
before buffers are saved.
whitespace-cleanup is a handy function, but putting it in
before-save-hook for every buffer is overkill, and causes messy diffs
when editing third-party code that did not initially have clean whitespace.
Additionally, whitespace preferences are often project-specific, and
it's inconvenient to set up before-save-hook in a .dir-locals.el file.
whitespace-cleanup-mode is a minor mode which calls whitespace-cleanup
before saving the current buffer, but only if the whitespace in the buffer
was initially clean. It determines this by quickly checking to see if
whitespace-cleanup would have any effect on the buffer.
If you choose not to use one of the convenient
packages in Melpa and Marmalade, you'll need to
add the directory containing whitespace-cleanup-mode.el to your load-path, and
then (require 'whitespace-cleanup-mode).
Enable whitespace-cleanup-mode in an individual buffer like this:
M-x whitespace-cleanup-mode
Optionally enable it everywhere by default using
global-whitespace-cleanup-mode. (You can override that by setting
whitespace-cleanup-mode to nil in file or directory local
variables.)
Alternatively, enable whitespace cleanup for a particular major mode:
(add-hook 'ruby-mode-hook 'whitespace-cleanup-mode)To enable it for an entire project, set whitespace-cleanup-mode to t in
your .dir-locals.el file.
This mode is built upon some functionality built into whitespace-mode, namely
whitespace-action: if you would rather see a warning when saving a file with
bogus whitespace, or even have the save aborted, then set that variable.
