Sourcemaps not ending up in the stream

[thany]

Please consider this task:

gulp.task("dist-build-css", () => {
  /* Compile Sass files using compass to the `css` directory, including sourcemaps and excluding line comments */
  return gulp.src([ "includes/sass/**/*.scss", "!includes/sass/**/_*.scss" ])
    .pipe(
      compass({
        sass: "includes/sass",
        css: "includes/css",
        style: "compressed",
        comments: true,
        sourcemap: true
      })
    )
    .pipe(gulp.dest("dist/includes/css"))
  ;
});

The problem here is that the sourcemap does not end up in the dist/includes/css directory, quite possibly because it's not included in the stream after compass() is done. This will make trouble if I need to further process it, for example if I want to fingerprint the files.

The config options css and sass are identical to my config.rb file, as instructed. When I set css to my dist directory, the sourcemap ends up there as expected, but it's still not included in the stream, so it won't be picked up by any subsequent plugins...

Or should I be using gulp-sourcemap to generate sourcemaps? That'll be trouble as well, since I need to exclude sass includes (starting with _) but they do need to go into sourcemaps.