async load({filePath, isHmrEnabled, isSSR, isPackage}) {
      let dependencies = [];
      let codeToCompile = await fs.promises.readFile(filePath, 'utf-8');
      // PRE-PROCESS
      if (preprocessOptions !== false) {
        ({code: codeToCompile, dependencies} = await svelte.preprocess(
          codeToCompile,
          preprocessOptions,
          {
            filename: filePath,
          },
        ));
      }

      // in dev mode, track preprocess dependencies
      if (isDev && dependencies && dependencies.length) {
        dependencies.forEach((imp) => addImportsToMap(filePath, imp));
      }

      const finalCompileOptions = {
        generate: isSSR ? 'ssr' : 'dom',
        css: isPackage ? true : false,
        ...compilerOptions, // Note(drew) should take precedence over generate above
        dev: isHmrEnabled || isDev,
        outputFilename: filePath,
        filename: filePath,
      };

      const compiled = svelte.compile(codeToCompile, finalCompileOptions);
      const {js, css} = compiled;

      if (useSourceMaps) {
        js.code = inlineSourcemap(js.code, js.map);
      }

      const output = {
        '.js': {
          code: js.code,
          map: useSourceMaps ? js.map : undefined,
        },
      };

      if (isHmrEnabled && !isSSR) {
        output['.js'].code = makeHot({
          id: filePath,
          compiledCode: js.code,
          hotOptions: {
            preserveLocalState: true,
            injectCss: true,
            ...hmrOptions,
            absoluteImports: false,
            noOverlay: true,
          },
          compiled,
          originalCode: codeToCompile,
          compileOptions: finalCompileOptions,
        });
      }

      if (!finalCompileOptions.css && css && css.code) {
        output['.css'] = {
          code: css.code,
          map: useSourceMaps ? css.map : undefined,
        };
      }
      return output;
    }
When a file changes, also mark it's importers as changed.
svelte.preprocess returns a list of preprocess deps - https://svelte.dev/docs#svelte_preprocess