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, 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.
