We should provide existing absolute paths for the source files

[mightyaleksey]

Recently, I had few problems with resolving paths in the postcss-url plugin.

I did a small research and found out that we provide non-existing absolute paths to the process() method.

I made two PRs which fix the problem: #25, css-modules/postcss-modules-scope#15
Unfortunately, those are breaking changes and we should publish them with new major version.

Also I haven't checked css-modulesify yet.

[mightyaleksey]

Ah, and we need opportunity to pass the to option to the postcss.process() method: https://github.com/postcss/postcss/blob/master/docs/api.md#processorprocesscss-opts

[tinchoz49]

👍 I have the same problem of @sullenor ! using postcss-copy.