Bundler gem installation mechanism for Bundler buildpack

[leondmello]

Why does the bundler buildpack install pre-built bundler binaries instead of using gem to install the appropriate version?

[sophiewigmore]

I'm not sure if that was ever considered in the original implementation, cc @ryanmoran incase he has historical context.
That seems like a viable option! I think that the way the buildpack installs the binary now is more consistent with how we install tools across the project and collect metadata.

[ryanmoran]

The historical context is that we want to make sure the buildpack can be made to support offline platforms. If the buildpack uses gem then its going to need a network connection to fetch the bundler gem.

[robdimsdale]

I'm not familiar enough with the gem install process to know if we could leverage it in an offline environment. If we could do that, it could be worth exploring.

[fg-j]

Since I'm working on moving bundler dependency management out of the dep server now, I can investigate briefly whether it'd be possible to use gem install for bundler offline.

[ryanmoran]

The biggest requirement to meet would be that we want bundler installed in its own layer, not into the gems directory under the mri layer, which is what gem install would likely do unless you override its configuration.