Plugins run twice on css modules

Hi,

I’m still investigating the issue but wanted some feedback:

postcss({
  modules: true,
  extract: true,
  plugins: [
    require('postcss-custom-properties')({ preserve: true })
  ],
})

Result:

.Button_primary__1gH9y {
  color: green;
  color: green;
  color: var(--color-primary);
}

I did some logging and the postcss-custom-properties is run twice on the same css module, hence the duplicate fallback.

1st

.primary {
  color: var(--color-primary);
}

2nd

.Button_primary__1gH9y {
  color: green;
  color: var(--color-primary);
}

[Anidetrix]

@n370 @Himself65 this change breaks such plugins as postcss-import, cause imported classes won’t be modularized

[pascalduez]

The issue is still alive: rollup-plugin-postcss@3.1.4