js-routes: Allow precompilation of routes.js file in development.

[david-yz-liu]

Motivation and Context

It looks like running MarkUs with Docker on WSL 2 runs into a webpacker compilation error:

Uncaught Error: Module build failed (from ./node_modules/rails-erb-loader/index.js):
Error: rails-erb-loader failed with code: 1
    at ChildProcess.<anonymous> (/app/node_modules/rails-erb-loader/index.js:128:16)
    at ChildProcess.emit (events.js:314:20)
    at maybeClose (internal/child_process.js:1022:16)
    at Socket.<anonymous> (internal/child_process.js:444:11)
    at Socket.emit (events.js:314:20)
    at Pipe.<anonymous> (net.js:675:12)
    erb application-b86bd25d2c8459646289.js:12001

I tried out various approaches in usabilityhub/rails-erb-loader#63 but didn't find one that worked (setting DISABLE_SPRING to 1, using bundle exec). When I inspect the webpack-dev-server output I see some permission errors associated with running rails, which rails-erb-loader does in a separate process.

webpacker_1  | Rails Error: Unable to access log file. Please ensure that /app/log/development.log exists and is writable (ie, make it writable for user and group: chmod 0664 /app/log/development.log). The log level has been raised to WARN and the output directed to STDERR until the problem is fixed.
webpacker_1  | Traceback (most recent call last):
webpacker_1  |  60: from bin/rails:9:in `<main>'
...
webpacker_1  |   3: from /app/config/initializers/bullet.rb:6:in `<top (required)>'
webpacker_1  |   2: from /bundle/gems/bullet-6.1.4/lib/bullet.rb:128:in `bullet_logger='
webpacker_1  |   1: from /bundle/gems/bullet-6.1.4/lib/bullet.rb:128:in `open'
webpacker_1  | /bundle/gems/bullet-6.1.4/lib/bullet.rb:128:in `initialize': Permission denied @ rb_sysopen - /app/log/bullet.log (Errno::EACCES)

Your Changes

Description: I've introduced a workaround to precompile the js-routes file by doing rails js:routes, which generates app/javascript/routes.js. If present, this file will be imported by application.js instead of routes.js.erb.

Type of change (select all that apply):

• Other (please specify): Development setup change

Testing

I verified that this allows webpacker to compile all of the required assets, so MarkUs can actually run!

Questions and Comments (if applicable)

I changed the extension .erb to .js.erb to allow webpacker to find routes.js.erb. We don't have any other assets that use the .erb extension (e.g., .css.erb), but if we ever do want that, we'll need to add them separately to the extensions list in webpacker.config. But I think it's best to limit our use of rails-erb-loader until we can figure out the root cause of this WSL issue.

Checklist

• I have performed a self-review of my own code.
• I have fixed any Hound bot comments.
• I have verified that the TravisCI tests have passed.
• I have reviewed the test coverage changes reported on Coveralls.
• I have described any required documentation changes below.

Required documentation changes (if applicable)

I'm updating https://github.com/MarkUsProject/Markus/wiki/Developer-Guide--Set-Up-With-Docker to include setup instructions for WSL 2, and will include the js routes precompilation step for this platform.

[mishaschwartz]

Looks good. I just added the file to .dockerignore so that it won't be accidentally added to an image build