Getting webassets to work with Dart Sass

05 July 2019

The Ruby version of Sass has been deprecated, but is readily replaced with the Dart implementation.

$ brew install dart
$ brew install sass

Now the sass command will work pretty much the same as it did with the Ruby version.

However, some libraries that are based on the Ruby version may not work, as some options have been changed.

This was the case for using the webassets Python package with Pelican.

With dart-sass version 1.20.1 and webassets version 0.12.1, I got the following error:

Caught exception "FilterError: sass: subprocess returned
a non-success result code: 64, stdout=b'Could not find an 
option named "cache-location". [...]

To bypass the cache-location option, you need to comment out a few lines of code.

Open the file <python env>/site-packages/webassets/filter/, where <python env> is the path to your environment. In my case, it’s in my virtualenvs directory.

With that file open, comment out lines 164-170:

# if isinstance(self.ctx.cache, FilesystemCache):
#     args.extend(['--cache-location',
#                  os.path.join(orig_cwd,, 'sass')])
# elif not cd:
#     # Without a fixed working directory, the location of the cache
#     # is basically undefined, so prefer not to use one at all.
#     args.extend(['--no-cache'])

Now you should be able to use the assets plugin for Pelican without issue.