I needed Ruby in order to run `npm run-script docs` in Bootstrap's project, but I had not used Ruby and did not know much about it.
Native Extension Build Error from Bootstrap's `docs` Script
The command failed at first because the site of Bootstrap seems to be created with Jekyll, which works on Ruby, and I hadn't installed it. macOS (10.14.2) has ruby and gem by default, however, once running `sudo gem install jekyll`, it turned out to have some problem with native extension build because the ruby installation lacks some C header file.
Attempt with Ruby Installation by Homebrew
Then, I tried to install ruby by Homebrew (brew), and added required environmental set-up in ~/.bash_profile, which was mentioned at the end of installation. Then, the installation of Jekyll succeeded.
After that, I got back to `npm run-script docs`, but now it claimed it could not find jekyll, with an advice to run `bundle install`. As per the advice, I ran bundle install at the project root directory, and saw a failure with some error. Whatever the error is, first of all, I saw some warning message at the beginning of this command output, which mentioned that Bundler version I used (1.16.6) was older than the version that created the lockfile (1.17.1).
Trouble with Bundler 1.17.1 Installation
So, I ran `sudo gem install bundle`, but surprisingly, it didn't upgrade bundle to the latest, which was 1.17.1. In addition, I noticed that there's `bundler`, which looks the same as bundle. I was so confused. Looking around the Web to know more about those, and learnt that those are actually the same. However, as I experienced, passing the name `bundle` and `bundler` to `gem` command is different. In this case, `bundler` did the right thing, which provided the latest version as 1.17.1, and `bundle` didn't, where even `gem install bundle -v 1.17.1` replied that it didn't find the version. Hmm...
Eventually, `sudo gem install bundler` installed Bundler 1.17.1, and now, `bundle install` went through to the end successfully... which was what I wanted to see, but unfortunately, it was not. I got a native extension build error again. This time, it was for eventmachine. Accommodatingly again, the error message gave me an advice to make sure that `gem install eventmachine -v '1.2.7' --source 'https://rubygems.org/'` succeeds beforehand. I tried this command, and it succeeded... which I didn't expect to do.
Attempt with rbenv and rvm
Mysteriously, it looked as if some other Ruby version was used in some part of these builds during the command `bundler install`. I was completely upset at this phase. Because it is related to Ruby version handling, I tried rbenv, but it didn't help. It might be because I didn't set things up in a right way, but in the end, I gave up with it. Secondly, I tried rvm. I installed it as it is described in its home page, and installed Ruby 2.5.3 by running `rvm install '2.5.3'`.
At this stage, I thought I should remove what I added to .bash_profile for the Ruby installed by Homebrew. While removing the lines, I noticed there was one additional line that I think was added by rvm installation, which looked like `[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"`. Applying this change in .bash_profile in the terminal, I could see Ruby version with the command `ruby -v`. I hoped it would make `sudo gem install bundler` work.
And it worked! I got bundler 1.17.1, and when I ran `bundler install`, I didn't get the warning message this time, and moreover, it succeeded!! Then, finally, I got all the way back to `npm run-script docs` in Bootstrap project, and the script finished successfully without any problem.
Conclusion
I recommend using Ruby Version Management (rvm) when you get some Ruby-related build problem in macOS. Installing and managing Ruby versions with rvm helped in my case with Bundler installation and Bootstrap `docs` script run.
