gulpfile.js

var gulp = require('gulp'),
    pug = require('gulp-pug'),
    less = require('gulp-less'),
    path = require('path'),
    htmlhint = require('gulp-htmlhint');

// SOURCES CONFIG
var source = {
    templates: {
        app: {
            files: ['demo/pug/index.pug'],
            watch: ['demo/pug/*.pug']
        }
    },
    styles: {
        app: {
            main: ['yamm/yamm.less'],
            dir: 'yamm',
            watch: ['yamm/yamm.less']
        }
    }
};

// BUILD TARGET CONFIG
var build = {
    styles: './yamm',
    templates: {
        app: './'
    }
};

// Error handler
function handleError(err) {
    console.log(err.toString());
    this.emit('end');
}

//---------------
// TASKS
//---------------

// LESS
gulp.task('yamm', function() {
    return gulp
        .src(source.styles.app.main)
        .pipe(
            less({
                paths: [source.styles.app.dir]
            })
        )
        .on('error', handleError)
        .pipe(gulp.dest(build.styles));
});

// PUG
gulp.task('templates', function() {
    return gulp
        .src(source.templates.app.files)
        .pipe(
            pug({
                pretty: true
            })
        )
        .on('error', handleError)
        .pipe(htmlhint())
        .pipe(htmlhint.reporter())
        .pipe(gulp.dest(build.templates.app));
});

//---------------
// WATCH
//---------------

// Watch changes
gulp.task('watch:demo', function() {
    gulp.watch(source.templates.app.watch, gulp.series('templates'));
});

gulp.task('watch:yamm', function() {
    gulp.watch(source.styles.app.watch, gulp.series('yamm'));
});

//---------------
// DEFAULT TASK
//---------------

gulp.task('default', gulp.series('yamm', 'watch:yamm'));

//---------------
// DEMO TASK
//---------------

gulp.task('demo', gulp.series('yamm', 'templates', gulp.parallel('watch:yamm', 'watch:demo')));