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Why is merge-stream requiring async completion signal?

I'm in the process of migrating from gulp#3.9.1 to gulp#4.0.2 and upgrading my gulp dependencies in the process. I have the following task in my gulpfile, where you can assume directories is just an array of directories I want to perform this operation on:
var gulp = require('gulp');
var ngAnnotate = require('gulp-ng-annotate'); //annotates dependencies in Angular components
var rev = require('gulp-rev'); //appends a hash to the end of file names to eliminate stale cached files
var revReplace = require('gulp-rev-replace');
var uglify = require('gulp-uglify'); // minimizes javascript files
var compressCss = require('gulp-minify-css');
var useref = require('gulp-useref'); // replaces style and script blocks in HTML files
var filter = require('gulp-filter');
var merge = require('merge-stream');
var sourcemaps = require('gulp-sourcemaps');
function minify() {
var tasks = directories.map(function (directory) {
var cssFilter = filter("**/all.min.css", {restore:true});
var jsAppFilter = filter("**/app.min.js", {restore:true});
var jsFilter = filter("**/*.js", {restore:true});
return gulp.src(dstBasePath + directory + "index.html", {allowEmpty: true})
.pipe(useref())
.pipe(cssFilter)
.pipe(compressCss({keepSpecialComments:false}))
.pipe(rev())
.pipe(cssFilter.restore)
.pipe(jsAppFilter)
.pipe(sourcemaps.init())
.pipe(ngAnnotate({add:true, single_quotes:true}))
.pipe(jsAppFilter.restore)
.pipe(jsFilter)
.pipe(uglify())
.pipe(rev())
.pipe(jsFilter.restore)
.pipe(revReplace())
.pipe(sourcemaps.write('.')) // sourcemaps need to be written to same folder for Datadog upload to work
.pipe(gulp.dest(dstBasePath + directory))
});
return merge(tasks);
}
Why would this result in the error "Did you forget to signal async completion?" from Gulp when running the task? Note that I'm using Gulp 4. I've tried passing a callback done to this task, and adding .addListener('end', done) to the final pipe, but this causes my merged stream to end prematurely (presumably when the first one ends). So perhaps one of these plugins is not signaling when it's completed, but how would you even get this to work otherwise? Thanks for any insight you can provide.

return merge(folders.map(function (folder) { // this has worked for me in the past
as has this form without merge
gulp.task('init', function (done) {
var zips = getZips(zipsPath);
var tasks = zips.map(function (zip) {
return gulp.src(zipsPath + "/" + zip)
.pipe(unzip({ keepEmpty: true }))
.pipe(gulp.dest(path.join("src", path.basename(zip, ".zip"))))
.on('end', function() { // this bit is necessary
done();
});
});
return tasks;
});

Gulp 4 requires that you signal async completion. There's some good information about it in this answer to a similar question:
Gulp error: The following tasks did not complete: Did you forget to signal async completion?
I had a similar case where I was returning a merged set of tasks, and I was able to resolve the error by making the function async and awaiting the merge. My case looked something like this:
gulp.task("build", async function () {
...
return await merge(tasks);
});
so I think you should be able to do something like
async function minify(){
...
return await merge(tasks);
}

Detect what file change with gulp

I have this gulpfile:
var gulp = require('gulp'),
concat = require('gulp-concat'),
uglify = require('gulp-uglify');
gulp.task('minifyJS', function() {
return gulp.src(['src/*.js'])
.pipe(uglify())
.pipe(gulp.dest('min'));
});
gulp.task('watch', function() {
gulp.watch(['src/*.js'], ['minifyJS']);
});
I want to know what file trigger the watcher and his absolute path.
For example: if my project is placed in /myCode and I change the file src/main.js, I want to see /myCode/src/main.js inside minifyJS task. Is there a way to do it?
Thank you for your time.

You can do it by using gulp-ng-annotate and gulp-changed:
var gulp = require('gulp');
var changed = require('gulp-changed');
var rename = require('gulp-rename');
var ngAnnotate = require('gulp-ng-annotate'); // just as an example
var SRC = 'src/*.js';
var DEST = 'src/';
//Function to get the path from the file name
function createPath(file) {
var stringArray = file.split('/');
var path = '';
var name = stringArray[1].split('.');
stringArray = name[0].split(/(?=[A-Z])/);
if (stringArray.length>1) {stringArray.pop()};
return {folder: stringArray[0], name: name[0]}
}
gulp.task('default', function () {
return gulp.src(SRC)
.pipe(changed(DEST))
// ngAnnotate will only get the files that
// changed since the last time it was run
.pipe(ngAnnotate())
.pipe(rename(function (path) {
var createdPath = createPath(path);
path.dirname = createdPath.folder;
path.basename: createdPath.name,
path.prefix: "",
path.suffix: "",
path.extname: ".min.js"
}))
.pipe(gulp.dest(DEST));
});
Result:

Use gulp-changed npm package.
$ npm install --save-dev gulp-changed
Try the below in gulp file, (I haven't tried)
var gulp = require('gulp'),
concat = require('gulp-concat'),
uglify = require('gulp-uglify'),
changed = require('gulp-changed');
gulp.task('minifyJS', function() {
return gulp.src(['src/*.js'])
.pipe(changed('min'))
.pipe(uglify())
.pipe(gulp.dest('min'));
});
gulp.task('watch', function() {
gulp.watch(['src/*.js'], ['minifyJS']);
});
see the documentation of this package https://www.npmjs.com/package/gulp-changed

Based on your comment to Julien's answer this should be fairly close to what you want, or at least get you going in the right direction:
var gulp = require('gulp'),
concat = require('gulp-concat'),
uglify = require('gulp-uglify'),
cache = require('gulp-cached'),
rename = require('gulp-rename'),
path = require('path');
function fileName(file) {
return file.dirname + path.sep + file.basename + file.extname;
}
gulp.task('minifyJS', function() {
return gulp.src(['src/*.js'])
.pipe(cache('minifyJS'))
.pipe(rename(function(file) {
var nameOfChangedFile = fileName(file);
if (nameOfChangedFile == './main.js') {
file.basename = 'main.min'
}
if (nameOfChangedFile == './userView.js') {
file.basename = 'user/userView.min'
}
console.log(nameOfChangedFile + ' -> ' + fileName(file));
}))
.pipe(uglify())
.pipe(gulp.dest('min'));
});
gulp.task('watch', function() {
gulp.watch(['src/*.js'], ['minifyJS']);
});
This uses gulp-cached to keep an in-memory cache of all the files in your src/ folder that have passed through the stream. Only files that have changed since the last invocation of minifyJS are passed down to the gulp-rename plugin.
The gulp-rename plugin itself is then used to alter the destination path of the changed files.
Note: the cache is empty on first run, since no files have passed through the gulp-cached plugin yet. This means that the first time you change a file all files in src/ will be written to the destination folder. On subsequent changes only the changed files will be written.

gulp-concat : from unknown source to the same destination

I recently started to use gulp to keep my dev project organized and I've run into a little something that I cant figure out. So this is my task :
gulp.task('jsassemble', function () {
return gulp
.src('vendor/proj/**/**/src/assets/js/*.js')
.pipe(concat('all.js'))
.pipe(gulp.dest('public/js'));
});
As you can see, it'll fetch every js file in vendor/proj/anyFolder/anySubFolder/src/assets/js, put them together, rename the newly created js 'all.js' and then put it in public/js. The problem is that I would like to have gulp to keep the folder hierarchy, for example :
Source = vendor/proj/anyFolder1/anySubFolder1/src/assets/js/*.js
Destination = public/js/anyFolder1/anySubFolder1/src/assets/js/all.js
Source = vendor/proj/anyFolder1/anySubFolder2/src/assets/js/*.js
Destination = public/js/anyFolder1/anySubFolder2/src/assets/js/all.js
Instead of simply having everything on those folder into a 1 and only public/js/all.js
Is there anyway to do it ? I've tried to google it first but I wasn't able to properly formulate my question in a few words and was given not-wanted results :/

You could create the function which keep your folder hierarchy. In this page (http://www.jamescrowley.co.uk/2014/02/17/using-gulp-packaging-files-by-folder/) you find the solution.
var fs = require('fs');
var path = require('path');
var es = require('event-stream');
var gulp = require('gulp');
var concat = require('gulp-concat');
var rename = require('gulp-rename');
var uglify = require('gulp-uglify');
var scriptsPath = './src/scripts/';
function getFolders(dir){
return fs.readdirSync(dir)
.filter(function(file){
return fs.statSync(path.join(dir, file)).isDirectory();
});
}
gulp.task('scripts', function() {
var folders = getFolders(scriptsPath);
var tasks = folders.map(function(folder) {
return gulp.src(path.join(scriptsPath, folder, '/*.js'))
.pipe(concat(folder + '.js'))
.pipe(gulp.dest(scriptsPath))
.pipe(uglify())
.pipe(rename(folder + '.min.js'))
.pipe(gulp.dest(scriptsPath));
});
return es.concat.apply(null, tasks);
});

Thanks to #caballerog who puts my on the right path, here's the explained code :
//get every folder from a 'pathTo/Something'
function getFolders(dir){
return fs.readdirSync(dir)
return fs.statSync(path.join(dir, file)).isDirectory();
}
var projectsRoot = 'vendor/proj/';
var pathToJsFiles = '/src/assets/js/';
var pathToPublic = 'public/js/';
gulp.task('scripts', function() {
var sites = [];
var pathToProjects = [];
// Fetching every folders in vendor/proj
projects = getFolders(projectsRoot);
// Fetching every subfolder in vendor/proj/something
for(index in projects){
sites.push(getFolders(projectsRoot + '/' + projects[index]));
}
// Pushing every projects/site that exists into an array
for(var i=0;i<projects.length;i++){
for(var j=0; j<sites.length; j++)
if(sites[i][j] != null)
pathToProjects.push(projects[i] + '/' + sites[i][j]);
}
// Fetching every JS on vendor/proj/pathToAProject/pathToJsFiles
// concatenate them together
// and sending them to pathToPublic/pathToAProject/all.js
var tasks = pathToProjects.map(function(pathToAProject) {
return gulp.src( projectsRoot + pathToAProject + pathToJsFiles + '/*.js')
.pipe(concat('all.js'))
.pipe(gulp.dest(pathToPublic + pathToAProject));
});
return es.concat.apply(null, tasks);
});
TL:DR = get every JS file in pathToPublic/someFolder/someFolder/PathToJS.

Gulp watch not called from within Nodemon

So I have my Gulp file as below.
The 'watch' block seems to work absolutely fine, and do what is expected. Nodemon works in the way that it detects file changes and refreshes the server, that works too.
But I can't for the life of me get Nodemon to call the 'watch' method when a file changes.
On line 81, the .on('start' is called succesfully from nodemon, but the code inside the 'watch' method is never executed.
var gulp = require('gulp');
var gutil = require('gulp-util'); // For logging stats and warnings
var jshint = require('gulp-jshint'); // For checking JavaScript for warnings
var concat = require('gulp-concat'); // For joining together multiple files
var uglify = require('gulp-uglify'); // For minimising files
var coffee = require('gulp-coffee'); // For compiling coffee script into js
var cofLint = require('gulp-coffeelint');// For checking coffee script for errors
var less = require('gulp-less'); // For compiling Less into CSS
var cssLint = require('gulp-csslint'); // For checking the awesomeness of css
var minCss = require('gulp-minify-css');// For minifying css
var uncss = require('gulp-uncss'); // For deleting unused CSS rules
var footer = require('gulp-footer'); // For adding footer text into files
var nodemon = require('gulp-nodemon'); // For the super cool instant refreshing server
var bSync = require('browser-sync'); // Syncs the place between multiple browsers for dev
var es = require('event-stream'); // For working with streams rather than temp dirs
var sourcePath = "sources";
var destPath = "public";
var jsFileName = "all.min.js";
var cssFileName = "all.min.css";
var footerText = "";
/* JavaScript Tasks */
gulp.task('scripts', function(){
var jsSrcPath = sourcePath + '/javascript/**/*';
var jsResPath = destPath + '/javascript';
var jsFromCs = gulp.src(jsSrcPath+'.coffee')// Get all coffee script
.pipe(cofLint()) // Check CS for errors or warnings
.pipe(cofLint.reporter()) // Output the error results
.pipe(coffee()); // Convert coffee to vanilla js
var jsFromPlain = gulp.src(jsSrcPath+'.js');// get all vanilla JavaScript
return es.merge(jsFromCs, jsFromPlain) // Both js from cs and vanilla js
.pipe(jshint()) // Check js errors or warnings
.pipe(jshint.reporter('jshint-stylish')) // Print js errors or warnings
.pipe(concat(jsFileName,{newLine: ';'})) // Concatenate all files together
.pipe(uglify()) // Minify JavaScript
.pipe(footer(footerText)) // Add footer to script
.pipe(gulp.dest(jsResPath)); // Save to destination
});
/* CSS Tasks */
gulp.task('styles', function(){
var cssSrcPath = sourcePath + '/styles/**/*';
var cssResPath = destPath + '/stylesheet';
var cssFromLess = gulp.src(cssSrcPath+'.less') // Get all Less code
.pipe(less()); // Convert Less to CSS
var cssFromVanilla = gulp.src(cssSrcPath+'.css');// Get all CSS
return es.merge(cssFromLess, cssFromVanilla) // Combine both CSS
.pipe(cssLint()) // Check CSS for errors or warnings
.pipe(cssLint.reporter()) // And output the results
.pipe(concat(cssFileName)) // Concatenate all files together
.pipe(minCss({compatibility: 'ie8'})) // Minify the CSS
.pipe(gulp.dest(cssResPath)); // Save to destination
});
/* Configure files to watch for changes */
gulp.task('watch', function() {
gulp.watch(sourcePath+'/**/*.{js,coffee}', ['scripts']);
gulp.watch(sourcePath+'/**/*.{css,less}', ['styles']);
});
/* Start Nodemon */
gulp.task('demon', function () {
nodemon({
script: './bin/www',
ext: 'js coffee css less html',
env: { 'NODE_ENV': 'development'}
})
.on('start', ['watch'])//TODO: ERROR: watch is never called, even though start is called
.on('change', ['watch'])
.on('restart', function () {
console.log('restarted!');
});
});
/* Default Task */
gulp.task('default', ['demon']);
Any suggestions why this may be happening?
Is there something wrong with my Gulp file?
(and yes, I know the code is a little over-commented, I work with apprentices and they like English better than code ;)

The problem is that Nodemon and browser-sync both need to be running. This code works:
gulp.task('nodemon', function (cb) {
var called = false;
return nodemon({
script: './bin/www',
watch: ['source/**/*']
})
.on('start', function onStart() {
if (!called) { cb(); }
called = true;
})
.on('restart', function onRestart() {
setTimeout(function reload() {
bSync.reload({
stream: false
});
}, 500);
});
});
gulp.task('browser-sync', ['nodemon', 'scripts', 'styles'], function () {
bSync.init({
files: ['sources/**/*.*'],
proxy: 'http://localhost:3000',
port: 4000,
browser: ['google chrome']
});
gulp.watch(sourcePath+'/**/*.{js,coffee}', ['scripts']);
gulp.watch(sourcePath+'/**/*.{css,less}', ['styles']);
gulp.watch("sources/**/*").on('change', bSync.reload);
gulp.watch("views/**/*.jade").on('change', bSync.reload);
});
/* Default Task */
gulp.task('default', ['clean', 'browser-sync']);

Gulp task apply uglify if file in pipe is javascript

I want to check if the file in the pipe is .js or not (it could be .map, .html, ...). And if so, uglifying it before copying it in the correct path.
ʕ •́؈•̀) I've try something like this (which not working):
gulpfile.js
gulp.src(current + '/**/*', {base: current})
.pipe($.tap(function (file) {
if (path.extname(file.path) === '.js') {
return gulp.src(file.path)
.pipe($.uglify());
}
}))
.pipe(gulp.dest(destination + '/' + name));
But for now, the uglify seems to do nothing...
Is anyone have a clue on how to do this ? (╥﹏╥)

If you're open to using plugins there is one called gulp-filter that does what you're asking for. https://www.npmjs.com/package/gulp-filter
It would probably look something like this
var gulp = require('gulp');
var gulpFilter = require('gulp-filter');
gulp.task('default', function () {
// create filter instance inside task function
var jsfilter = gulpFilter('**/*.js', {restore: true});
return gulp.src(current + '/**/*', {base: current})
// filter a subset of the files
.pipe(jsFilter)
// run them through a plugin
.pipe($.uglify())
// bring back the previously filtered out files (optional)
.pipe(jsFilter.restore)
.pipe(gulp.dest(destination + '/' + name));
});

try using gulp-filter
something like
var filter = require('gulp-filter');
var jsFilter = filter('**/*.js');
gulp.src('*/*')
.pipe(jsFilter)
.pipe(uglify)