onChange({filePath}) {
      const filePathNoExt = stripFileExtension(filePath);
      // check exact: "_index.scss" (/a/b/c/foo/_index.scss)
      this._markImportersAsChanged(filePath);
      // check no ext: "_index" (/a/b/c/foo/_index)
      this._markImportersAsChanged(filePathNoExt);
      // check no underscore: "index.scss" (/a/b/c/foo/index.scss)
      this._markImportersAsChanged(filePath.replace(PARTIAL_REGEX, '$1$2'));
      // check no ext, no underscore: "index" (/a/b/c/foo/index)
      this._markImportersAsChanged(filePathNoExt.replace(PARTIAL_REGEX, '$1$2'));
      // check folder import: "foo" (/a/b/c/foo)
      if (filePathNoExt.endsWith('_index')) {
        const folderPathNoIndex = filePathNoExt.substring(0, filePathNoExt.length - 7);
        this._markImportersAsChanged(folderPathNoIndex);
      }
    }
When a file changes, also mark it's importers as changed.
Note that Sass has very lax matching of imports -> files.
Follow these rules to find a match: https://sass-lang.com/documentation/at-rules/use