Support reconfigurable modules via "@forward ... with"

Edited by @nex3

• Proposal
• Specs
• Documentation
• Dart Sass
• LibSass

The current plan is to add a with clause to @forward. This would work like the same clause in @use, except that unconfigured variables or variables set with the !default flag would still be configurable by the modules loading the module in which the @forward appears. For example:

@forward "unopinionated" with (
  $hue: 0 !default, // Can be overridden by upstream users.
  $saturation: 50% // Cannot be overridden by upstream users.
);

---

I’ve been moving my Sass packages over to the module system, but I keep hitting a problem I can’t figure out. I usually have a central set of configuration variables that need to:

• be configurable by users
• be used by all the internal modules

But any time I make an internal file available to other files, I lose the ability to take user-configurations:

Error: This module was already loaded, so it can't be configured using "with".

I’ve tried adding duplicate !default settings in each file that needs, but then I get:

Error: Module sass/_config.scss and the new module both forward a variable named $setting.

As far as I can tell, everything that uses a particular default variable has to live in the same file?

Is this how it’s meant to work? How would you recommend handling global package config shared among partials?

[nex3]

You’ve found a bug! It looks like it’s even a bug in the spec: when you load a module with a config and that module forwards multiple modules, the config is passed as-is to all those modules, which will basically never do what you want. We need to be more sophisticated about how we handle that interaction.

[nex3]

The proposal has landed! I’m going to give it a couple weeks to accumulate feedback, and then move forward on implementation.