Detangle NODE_ENV and RAILS_ENV

[gauravtiwari]

In earlier versions of webpacker we have used Rails env as fallback env, which isn't ideal because both NODE_ENV and RAILS_ENV has different meaning for different environments.

For example: setting NODE_ENV=production means the webpacker will compile assets in production mode however at same time RAILS_ENV can be staging. Webpack and node libraries only understands development and production environments. However, it's normal to have many custom RAILS_ENV.

This PR makes RAILS_ENV and NODE_ENV independent of each other for clarity.

---

Examples:

# will compile in production mode but will use staging settings from webpacker.yml (if present or else fallback to production config)
RAILS_ENV=staging bundle exec rails webpacker:compile
# will use foo env settings from webpacker.yml but will compile in production mode
RAILS_ENV=foo bundle exec rails webpacker:compile

By default binstubs will use NODE_ENV=development however rake compile task will compile in production mode:

# Compiles in development mode by default
./bin/webpack
./bin/webpack-dev-server

# Compiles in production mode
NODE_ENV=production ./bin/webpack
NODE_ENV=production ./bin/webpack-dev-server

# compiles in production mode by default (unless NODE_ENV is supplied) - same as sprockets
bundle exec rails assets:precompile
bundle exec rails webpacker:compile

TODO:

• Fix tests

[Systho]

THIS !
Thank you very much for having thought of this :)

[tricknotes]

@gauravtiwari
This PR is pretty awesome!
Could you release a new version with this change?

[gauravtiwari]

Made a new release 👍