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Magento 2 module which allows compiling less files using the less.js compiler

Description

This module was built out of frustration about the slow deployments of static assets to a production environment while running bin/magento setup:static-content:deploy. In particular this module tries to tackle the slowness which comes with compiling less files using the less.php library, which Magento 2 uses by default.
This module provides a solution by using the original less.js compiler which was written in javascript and is executed through node.js
We have benchmarked the difference between the less.php and less.js compilers, and the less.js compiler is somewhere between 1.5 and 3 times as fast as the less.php compiler, although it depends on your PHP version. If you run PHP 5.x the performance increase will be much higher, PHP 7.x is actually quite fast by itself, but the nodejs version still beats it.

Update: Since Magento 2.3.0, it seems like the performance differences between less.php and less.js are not very big anymore. I have the suspicion this might have something to do with newer releases of the less.php library. Which got released somewhere around the period when Magento 2.2.3 & 2.1.12 were released. So it's possible that the performance difference for Magento 2.2.x and 2.1.x might also be less significant then how it's displayed below if you upgrade the less.php library to the latest version (v1.7.0.14 at the time of writing).
This is a bit of speculation, since unfortunately I didn't keep track of the version of the less.php library which I've used in the benchmarks, so I'm not sure about this statement.

Since Magento 2.4.0 (or newer PHP versions?), the performance differences seems to have changed in favor of less.php. But you might still want to use this module so that the outputted css is the same between your local development environment and a production environment.

Requirements

You'll need at least Magento 2.0.7. We didn't bother with testing this module on older versions.
If you want to use this module, you'll need to be able to install node.js and npm on the machine(s) on which you will build your static assets.
You'll also need to make sure that the node binary is available in the $PATH environment variable of the user which will build the static assets.
You'll also need composer to add this module to your Magento 2 shop.

Installation

First, we recommend you to install the less compiler itself, and save it into your package.json file as a production dependency:

Watch out: from Magento 2.1 onwards, the package.json file is being renamed to package.json.sample to enable you to have your own nodejs dependencies without Magento overwriting this every time with its own version each time you update Magento. So if you use Magento >= 2.1 make sure you copy the package.json.sample file to package.json before running the above command if you want to work with Magento's grunt setup.

Then run a shrinkwrap, so the version of less (and its dependencies) are fixed, this will produce a file npm-shrinkwrap.json with the exact versions of all your nodejs production dependencies and their own dependencies, so you can be sure it will use those exact versions when you install this on another machine.

And make sure you add these two files to your version control system.

For an analogy with composer, you can compare the package.json file with composer.json, and npm-shrinkwrap.json with composer.lock

Now install this module

And enable it in Magento

As the last step, in your deploy scripts, make sure you call npm install --production. You should execute this somewhere between composer install and bin/magento setup:static-content:deploy

Configuration

You have the opportunity to configure the arguments we send to the lessc and node commands. The defaults are:

• lessc --no-color
• node --no-deprecation

If you want to override the default arguments, you can do this by modifying your app/etc/config.php or app/etc/env.php file and adding something like this:

You can also enable throwing an exception when the less compilation runs into warnings/errors, by default this is disabled and you should find the problems logged in your var/log/system.log file. But if you want to enable throwing an exception during the compilation process, you can by configuring this in your app/etc/config.php or app/etc/env.php file:

Investigating less compilation errors

When your .less files have a syntax error or contain something which doesn't allow it to compile properly, please have a look at the var/log/system.log file, it will contain some output about what caused the problem.

Remarks

1. Installing this module will effectively replace the default less compiler from Magento2. If you want to go back to the default less compiler, you need to disable this module or uninstall it.
2. This module expects the less compiler to exist in {MAGENTO_ROOT_DIR}/node_modules/.bin/lessc, this is a hard coded path which is being used in the module. The compiler will end up there if you follow the installation steps above, but if for some reason you prefer to install your nodejs modules someplace else, then this module won't work. If somebody actually has this problem and wants us to make this configurable, please let me know!
3. The default less processor in Magento 2 passes an option to the less compiler, which says it should compress the resulting css file. In this module, we have chosen not to do so, as we believe this isn't a task to be executed while compiling less files. It should be done further down the line, like for example during the minification phase. If someone disagrees with this, please let me know, I'm open to discussion about this.
4. This module was tested against Magento versions 2.0.7, 2.1.x, 2.2.x, 2.3.x, 2.4.x

Benchmarks

Intro

This is by no means very professionaly conducted, but here are some tests performed on some Magento 2 shops we are working on.
We disabled parallelism to make the comparison between different Magento versions easier to understand.
We only measured the duration of the bin/magento setup:static-content:deploy command, xdebug is disabled as it causes a massive slowdown, and before every run we make sure all caches are clean, by running:

Machines

• The older server is a server which is in constant use and has older software installed on it.
• The newer server is a new server which currently receives no traffic and has al the sparkly new software versions installed (at the time of writing).
• The older-local machine is a 2011 Macbook Pro (HDD has been upgraded to SSD, no vagrant or docker, just native software using Macports)
• The newer-local machine is a 2017 Macbook Pro (native software using Homebrew or Macports)

Results

* The quick strategy deployment is currently bugged in Magento 2.2.x and 2.3.x and 2.4.x and behaves the same as the standard strategy