Original discussion on this can be found toward the end of #115.

In 3.0.0, lessPlugins option as documented in the README doesn't appear to actually do anything.

If I instead specify less plugins in plugins, the cloneDeep() call in the loader's options processing will wipe the install function from each plugin, and a plugin.install is not a function will be emitted during processing.

What seems to work, assuming that lessPlugins is the desired approach, is adding this:

if (options.lessPlugins) { options.plugins.push.apply(options.plugins, loaderUtils.getOptions(this).lessPlugins); } 

immediately after the line:

options.plugins.push(webpackPlugin); 

In the loader.

I'd guess that cloneDeep() might not actually be what's desired here, but this approach matches the README.