Sass @forward rule and private member visibility

No, the current Sass specification does not allow for the explicit forwarding of private members. Any member prefixed with an underscore (e.g., $_internal-var) is strictly encapsulated within its defining module. The @forward rule only transmits public members; private members are stripped from the public API and remain inaccessible to any module that loads the forwarding module via @use.

The Encapsulation Logic

In the Sass module system, the underscore prefix is a hard boundary. This design ensures that internal implementation details cannot be accidentally depended upon by external consumers, preventing breaking changes when internal logic is refactored. Because @forward acts as a proxy for the module's public interface, it cannot "promote" a private member to public status.

Recommended Architectural Approach

To expose internal utilities without duplicating code or polluting the primary module's public API, you should move those utilities into a dedicated shared or internal module. This separates the implementation from the interface.

Implementation Strategy

1. Extract Utilities: Move the underscored members into a new file (e.g., _utilities.scss) and remove the underscore prefix to make them public within that specific file.
2. Forward the Utilities: In your main entry module, use @forward 'utilities'.
3. Maintain Internal Use: The primary module can still @use 'utilities' internally to perform its logic.

// _utilities.scss
$shared-spacing: 1rem; // Now public within this module

// _main.scss
@use 'utilities';
@forward 'utilities';

.component {
  padding: utilities.$shared-spacing;
}

Verification

To verify this behavior in your environment (assuming Dart Sass), you can run a simple test:

• Create _a.scss with $_private: 10px;.
• Create _b.scss with @forward 'a';.
• Create main.scss with @use 'b'; and attempt to access b.$_private.

The compiler will throw an error stating that $_private is not a member of module b, confirming that @forward ignores private members.