Creating rev-manifest file after gulp-rev runs in parallel

gulpfile.js

// I have a bunch of style/script tasks running in parallel which 
// were overwriting or garbling my rev-manifest.json file when using 
// gulp-rev directly.  It works great if you only have one task 
// but falls down when you have tasks running simultaneously as they 
// overwrite each other's changes in the manifest.  My approach runs 
// all of the processing in parallel but generates the manifest as a 
// second step in the 'build' task using the run-sequence plugin.

// Include gulp
var gulp = require('gulp');

// gulp tasks
var plumber = require('gulp-plumber');
var jshint = require('gulp-jshint');
var concat = require('gulp-concat');
var uglify = require('gulp-uglify');
var inject = require('gulp-inject');
var sass = require('gulp-sass');
var minifyCSS = require('gulp-minify-css');
var util = require('gulp-util');
var rev = require('gulp-rev');
var sourcemaps = require('gulp-sourcemaps');
var cached = require('gulp-cached');
var remember = require('gulp-remember');
// normal node module
var del = require('del');
var fs = require('fs');
var path = require('path');
var runSequence = require('run-sequence');

// namespace
var app = {}

// borrowed this function from gulp-inject
app.removeBasePath = function(basedir, filepath) {
	return [basedir].reduce(function (path, remove) {
		if (path[0] === '/' && remove[0] !== '/') {
		  remove = '/' + remove;
		}
		if (path[0] !== '/' && remove[0] === '/') {
		  path = '/' + path;
		    }
		    if (remove && path.indexOf(remove) === 0) {
		      return path.slice(remove.length);
		    }
		    return path;
		  }, filepath);
};

app.createManifest = function(assets, ignorePath) {
	var files = fs.readdirSync(assets);
	var relpath = app.removeBasePath(ignorePath, assets);
	var matches = {};

	for (var ii = 0; ii < files.length; ii++) {
		var f = files[ii];
		var ext = path.extname(f);
		if (ext == '.js' || ext == '.css') {
			// gulp-rev generates files like base-name-file-0123456789.ext where the hash is always 10 characters - we want everything up to that last hyphen before the hash
			matches[path.basename(f, ext).slice(0, -11) + ext] = relpath + f;
		}
	}

	// the 4 here causes it to pretty print the file for readability 
	fs.writeFileSync(assets + '/rev-manifest.json', JSON.stringify(matches, null, 4), 'utf-8');
};

app.addStyle = function(outputFilename, paths) {

	// remove existing files matching file*.css* (get both .css and .css.map)
	var glob = ['./app/assets/global/' + path.basename(outputFilename, path.extname(outputFilename)) + '*.css*'];
	del(glob);
	
	return gulp.src(paths)
				.pipe(plumber())
				.pipe(cached(outputFilename))
		    .pipe(sourcemaps.init())
		    .pipe(sass())
		    .pipe(minifyCSS({advanced: false}))
		    .pipe(remember(outputFilename))
		    .pipe(concat(outputFilename))
				.pipe(rev())
				.pipe(sourcemaps.write('.'))
		    .pipe(gulp.dest('./app/assets/global/'));

};

app.addScript = function(outputFilename, paths) {

	/* uglify options = {
            output: { // http://lisperator.net/uglifyjs/codegen
               // beautify: debug,
                //comments: debug ? true : /^!|\b(copyright|license)\b|@(preserve|license|cc_on)\b/i,
                semicolons: true
            },
            compress: { // http://lisperator.net/uglifyjs/compress, http://davidwalsh.name/compress-uglify
                sequences: !debug,
                booleans: !debug,
                conditionals: !debug,
                hoist_funs: false,
                hoist_vars: debug,
                warnings: debug,
            },
            mangle: false
        }
    */	

	// remove existing files matching file*.css* (get both .js and .js.map)
	var glob = ['./app/assets/global/' + path.basename(outputFilename, path.extname(outputFilename)) + '*.js*'];
	del(glob);

    return gulp.src(paths)
				.pipe(cached(outputFilename))
			  .pipe(sourcemaps.init())
		    .pipe(uglify({mangle: false}).on('error', util.log))
			  .pipe(remember(outputFilename))
		    .pipe(concat(outputFilename))
				.pipe(rev())
				.pipe(sourcemaps.write('.'))
				.pipe(gulp.dest('./app/assets/global/'));

};


//Lint Task
gulp.task('lint', function() {
    return gulp.src('./app/assets/js/*.js')
		  .pipe(cached('jslint'))
      .pipe(jshint())
	    .pipe(remember('jslint'))
      .pipe(jshint.reporter('default'));
});

gulp.task('styles:core', function() {
	return app.addStyle('core.css'
					,['./app/assets/css/core.css'
	             ,'./app/assets/css/core_print.css'
	             ,'./app/assets/css/jquery.datepicker.css'
	             ,'./app/assets/scss/core.scss']);
});

gulp.task('styles:helpscout', function() {
	return app.addStyle('helpscout.css'
					,['./app/assets/scss/bootstrap.scss']);
});


gulp.task('script:core', function() {
    return app.addScript('core.js'
    				,['./app/assets/js/library/jquery/jquery.js', 
    				,'./app/assets/js/forms/forms.js']
    				);
});

gulp.task('script:hotels', function() {
    return app.addScript('hotels.js'
    				,['./app/assets/js/hotels/hotels.js'
    				,'./app/assets/js/hotels/hotels-services.js'
    				,'./app/assets/js/hotels/hotels-display.js']
    				);
});


gulp.task('manifest', function() { 
	return app.createManifest('app/assets/global/', 'app/assets');
});


// meta tasks
gulp.task('styles', ['styles:core', 'styles:helpscout']);
gulp.task('scripts', ['script:core', 'script:hotels']);

gulp.task('build', function(cb) {
	runSequence(['styles', 'scripts'], 'manifest', cb);
});

// Watch Files For Changes
gulp.task('watch', function() {
    gulp.watch(['./app/assets/js/*.js'
                ,'./app/assets/css/*.css'
                ,'./app/assets/css/*.scss']
    		,['build']);
});

// Default Task
gulp.task('default', ['lint', 'inject', 'watch']);

Rather than use the built-in gulp-rev manifest functionality, I wrote my own little function to generate the file. It's quite simple to generate from a directory full of js/css files (excluding sourcemaps). The key is to use the run-sequence plugin in the 'build' task to generate the manifest after all of the style/script tasks have run in parallel.