If you run bundle install, you'll see the following list of errors:
Bundler could not find compatible versions for gem "does-not-exist":
In Gemfile:
dep2 was resolved to 0.0.1, which depends on
does-not-exist (= 1.0.0)
Could not find gem 'does-not-exist (= 1.0.0)', which is required by gem 'dep2', in any of the sources.
Bundler could not find compatible versions for gem "librato-metrics":
In Gemfile:
librato-metrics (= 1.5.0)
dependency was resolved to 0.0.1, which depends on
librato-metrics
The first error is legitimate: There is no version of "does-not-exist", so naturally, Bundler will not be able to find any compatible versions.
But the second error is spurious: Bundler did find a compatible version of librato-metrics. But
the error shows up because during the resolution process, the Molinillo library considered a
group of librato-metrics versions in the 2.x series, and rejected all of them (and stored the error
message in a data structure that is later used to generate the list of errors). But then it
considered another group of librato-metrics versions and found that version 1.5.0 is compatible
with both bundler-test and dependency (but it doesn't remove the error from the data structure because
that same data is used by for other purposes).
But the error message remains. I encountered an error like this while trying to upgrade a large, commercial project from Rails 4.x to Rails 5. It confused me, and there was nothing about it on Google or Stack Overflow (and when I posted my own question, nobody answered). So I debugged it myself until I found the cause (roughly).