Using gulp to compile bootstrap.less files into main bootstrap.css?

I had the same issues trying to compile the Bootstrap CSS. My simplified solution ended up looking like:

// Compiles LESS > CSS 
gulp.task('build-less', function(){
    return gulp.src('styles.less')
        .pipe(less())
        .pipe(gulp.dest('./source/css'));
});

and my styles.less file included the import to the bootstrap.less. I noticed that if the bootstrap less files were included in the gulp.src() path it would errors.

My styles.less:

@import "../lib/bootstrap/less/bootstrap.less";
@body-bg:     red; // test background color