What happened?

When an SCSS file uses a bare module specifier like @use 'Widget'; (Sass's "I'll figure out the extension" form), and there is both a Widget.tsx and a Widget.scss next to the importer, fallow resolves the import to Widget.tsx instead of Widget.scss.

This is incorrect: Sass's resolver only ever looks for Widget.scss / _Widget.scss / Widget.sass / _Widget.sass. The TypeScript file is invisible to Sass; it has no .scss content and Dart Sass / node-sass would error at build time if asked to import it. The Angular CLI, Nx, Vite, and webpack sass-loader all behave the same way.

The mis-resolution creates phantom circular dependencies when:

1. Widget.tsx imports ./Widget.scss (standard CSS-modules / Angular styleUrls pattern).
2. Widget.tsx imports ./Helper (a sibling component).
3. Helper.tsx imports ./Helper.scss.
4. Helper.scss does @use 'Widget'; — meant to share Sass variables/mixins from Widget.scss.

Fallow's graph then contains:

• Widget.tsx → Widget.scss ✓ (correct)
• Widget.tsx → Helper.tsx ✓ (correct)
• Helper.tsx → Helper.scss ✓ (correct)
• Helper.scss → Widget.tsx ❌ (should be → Widget.scss)

… which produces a 3-file cycle Helper.scss → Widget.tsx → Helper.tsx → Helper.scss that does not exist in reality.

Reproduction

1. Create an empty directory and cd into it.

2. Create a minimal .fallowrc.json:

   {
     "$schema": "https://raw.githubusercontent.com/fallow-rs/fallow/main/schema.json",
     "entry": ["src/main.tsx"]
   }

3. Create package.json:

   { "name": "demo", "private": true, "version": "0.0.1" }

4. Create src/Widget.tsx:

   import './Widget.scss';
   import { Helper } from './Helper';
   
   export function Widget() {
     return Helper();
   }

5. Create src/Widget.scss:

   .widget { color: red; }

6. Create src/Helper.tsx:

   import './Helper.scss';
   
   export function Helper() {
     return 'helper';
   }

7. Create src/Helper.scss — bare @use of the sibling Sass file (the bug trigger):

   @use 'Widget';
   
   .helper { background: blue; }

8. Create src/main.tsx:

   import { Widget } from './Widget';
   console.log(Widget());

9. Run fallow:

   fallow dead-code --format json --quiet | jq '{cnt: (.circular_dependencies | length), cycles: .circular_dependencies}'

Expected behavior

{ "cnt": 0, "cycles": [] }

@use 'Widget'; from a .scss importer must resolve only to *.scss / *.sass / _*.scss / _*.sass candidates per the Sass resolution algorithm. Widget.tsx is not a Sass file and must not be considered.

The control case verifies this: replace @use 'Widget'; with @use './Widget.scss'; (extension-explicit) and re-run — fallow correctly reports cnt: 0. The two forms are equivalent in Sass, so they should be classified identically.

Actual behavior

{
  "cnt": 1,
  "cycles": [
    {
      "files": ["src/Helper.scss", "src/Widget.tsx", "src/Helper.tsx"],
      "length": 3,
      "line": 1,
      "col": 0,
      "actions": [
        {
          "type": "refactor-cycle",
          "auto_fixable": false,
          "description": "Extract shared logic into a separate module to break the cycle",
          "note": "Circular imports can cause initialization issues and make code harder to reason about"
        },
        ...
      ]
    }
  ]
}

The cycle includes Widget.tsx, which Helper.scss cannot possibly reach via Sass's resolution algorithm.

Suggested fix

The SCSS-specific resolver in crates/graph/src/resolve/specifier.rs:197 (fn try_scss_fallbacks) calls a chain of three SCSS-aware resolvers (partial fallback, framework include-paths, node_modules), but if none of those produce a hit, the outer resolve_specifier continues into the generic alias / source-extension fallback chain — which is where Widget.tsx is matched.

A minimal fix: when the importer's extension is .scss / .sass, the resolver should return ResolveResult::Unresolved after exhausting the SCSS-specific fallbacks, instead of falling through to the JS/TS extension list. Equivalently, the generic source-extension fallback (try_source_fallback and the inline extensions retry in resolve_specifier) should consult is_style_file(from_file) and skip JS/TS extensions when the importer is a stylesheet.

(Note: Sass has its own pkg: import scheme for cross-language resolution. Even there, the targets are *.scss only, never *.tsx.)

Fallow version

2.56.0

Operating system

macOS

Configuration

`.fallowrc.json` shown above. There is no per-file or per-extension override for the resolver; the only way to silence the resulting cycle is `rules.circular-dependency: "off"` globally (which hides every cycle, real and phantom).