Document the default configuration of the transforms that cssnano uses

[nene]

Looking at cssnano docs I saw that it includes autoprefixer. So I thought, great, I don't need to include autoprefixer separately, cssnano will take care of adding all these prefixes. But when I tested it, it turned out that no prefixes get added.

After lots of debugging I finally saw the following lines in css-nano source code:

let defaultOptions = {
    autoprefixer: {
        add: false
    },

So that explains it... it's configured to only remove needless prefixes, but never add new ones. This makes sense for a minimizer, but it was contrary what I expected autoprefixer to do.

It would be really nice if this were documented. Also there are other plugins that are configured with similar defaults.

[ben-eb]

I think naming the option autoprefixer was the mistake here. I'm looking to review what we bundle by default for v4, and at least we should look at changing the name.

#88 (comment)

However this is documented in the optimisations section.

http://cssnano.co/optimisations/

[nene]

Indeed, didn't notice this page as I actually discovered cssnano through Webpack css-loader plugin, which in its documentation linked the options page. For some reason I thought that's the main page of the manual and didn't look further.

In the end I decided to disable cssnano. The css-loader kind of magically enabled it, but I don't really care about these micro-optimizations. It caught us by surprise when some css suddenly started to misbehave when compilation was switched to production mode. Apparently some selectors got merged overly aggressively. (Disabling the merge-rules transform eliminated that issue.) However I haven't been able to reproduce the issue with cssnano alone. For some reason the aggressive optimization only happened within Webpack. Strange stuff...

[ben-eb]

The defaults are now properly documented;

• http://cssnano.co/optimisations/#autoprefixer
• http://cssnano.co/optimisations/#convertvalues
• http://cssnano.co/optimisations/#normalizecharset

Going to mark this as resolved. 4.0 breaking changes are tracked in #88.