modify WEBPACKER PARALLEL environment variable.

[masato-hi]

Will be possible to specify the WEBPACKER PARALLEL environment variable from the command line.

We also added a document about WEBPACKER_PARALLEL.

The master branch is currently working on 6.x, so we need to merge after merging this pull request.
#2839

I'm not good at English, so I'm looking for opinions on better documentation.

ref: #2093

[gauravtiwari]

thanks @masato-hi Could you please use the above function isBoolean (line 2)?

[masato-hi]

Thanks for review.
The isBoolean function cannot handle "false" correctly

[pedrofurtado]

Hey, @masato-hi ! 👋

Thanks for your contribution!

For this purpose (modify WEBPACKER_PARALLEL environment variable for a specific environment, for example), this works for your scenario?

• Edit your config/webpack/[ENVIRONMENT].js and put at the top the desired value of WEBPACKER_PARALLEL, like this snippet code below:

process.env.WEBPACKER_PARALLEL = 'desired-value'
// ... existing code of file ...

Or this not works for you, and the PR in this case solves some problem related to it?

Let me know what you think about 🤝 🍻

[masato-hi]

@pedrofurtado Thanks for confirming.

It looks like it's working fine in my environment. 🤔 (The sed command installed on MacOSX may not execute the following code successfully.)

rails new myapp --webpack
cd myapp
sed -i -e "s/gem 'webpacker', '~> 5.0'/gem 'webpacker', github: 'masato-hi\/webpacker', branch: 'modify-webpacker-parallel-env'/" Gemfile
bundle install
yes | bundle exec rake webpacker:install
sed -i -e 's/"@rails\/webpacker": ".*"/"@rails\/webpacker": "masato-hi\/webpacker#modify-webpacker-parallel-env"/' package.json
yarn
echo "
process.env.NODE_ENV = process.env.NODE_ENV || 'production'
process.env.WEBPACKER_PARALLEL = '2'

const webpackConfig = require('./base')

console.log(webpackConfig.optimization.minimizer[0])
module.exports = webpackConfig
" > config/webpack/production.js
rm .browserslistrc # cheap tricks for "Error [BrowserslistError]: contains both .browserslistrc and package.json with browsers"
RAILS_ENV=production bundle exec rake webpacker:clean webpacker:compile

Output:

Compiling...
Compiled all packs in /tmp/myapp/public/packs
TerserPlugin {
  options: {
    test: /\.[cm]?js(\?.*)?$/i,
    extractComments: true,
    parallel: 2,
    include: undefined,
    exclude: undefined,
    minify: undefined,
    terserOptions: {
      parse: [Object],
      compress: [Object],
      mangle: [Object],
      output: [Object]
    }
  }
}
asset manifest.json 23 bytes [emitted]
webpack 5.21.2 compiled successfully in 26 ms

The value of "parallel" is 2.

The configuration only affects production builds.
You also need to set process.env.WEBPACKER_PARALLEL before require('@rails/webpacker') / require('./ base') is executed.

[masato-hi]

@gauravtiwari
The changes in docs/troubleshooting.md have been merged into master and are now reflected.
What do you think?

[olleolleolle]

I made some inline suggestions, hope this helps.

[olleolleolle]

Suggested change

	Check the link for details.
	https://webpack.js.org/plugins/terser-webpack-plugin/#parallel
	[`terser-webpack-plugin` documentation](https://webpack.js.org/plugins/terser-webpack-plugin/) has more details.

[olleolleolle]

Suggested change

	The parallel option of Tersor-Plugin is enabled in the production build, which may cause memory shortage.
	The parallel option of TerserWebpackPlugin is enabled in the production build, which may cause memory shortage.

[olleolleolle]

Suggested change

	## If an error occurs or times out during a production build on Continuous Integration (CI) services such as CircleCI, CodeShip, Travis CI
	## If an error occurs or times out during a production build

[justin808]

@guillaumebriday, For sure, we should do something with PR. Running out of memory causes a very confusing build just seems to hang when it's swapping memory.

I don't like the current default:

   parallel: Number.parseInt(process.env.WEBPACKER_PARALLEL, 10) || true,

Defaults should be defaults, which is true for this option.

How about this:

1. default to true
2. all env override of process.env.WEBPACKER_PARALLEL to either be false or some lower number to set on CI machines?

https://webpack.js.org/plugins/terser-webpack-plugin/#parallel

parallel
Type: Boolean|Number Default: true

Use multi-process parallel running to improve the build speed. Default number of concurrent runs: os.cpus().length - 1.

ℹ️ Parallelization can speedup your build significantly and is therefore highly recommended.

⚠️ If you use Circle CI or any other environment that doesn't provide real available count of CPUs then you need to setup explicitly number of CPUs to avoid Error: Call retries were exceeded (see #143, #202).

[justin808]

Feel free to reopen this PR here:
https://github.com/shakacode/shakapacker/pulls