how is the sass being transformed

[Gavin]

I'm a bit confused as to how the sass is being compiled. i've looked at the gulp file

.pipe(rename({ extname: '.css' }))
.pipe(sourcemaps.init())
.pipe(postcss([vars, extend, nested, autoprefixer, cssnano]))
.pipe(sourcemaps.write('.'))
.pipe(gulp.dest(paths.dist))
.pipe(reload({ stream: true }));

I'm used to seeing something like "gulp-sass" of "gulp-plugins". Which process if compiling the sass in css?