Test truffleruby support on Travis CI

.travis.yml

@@ -36,9 +36,19 @@ matrix:
     - rvm: 2.1.10
       env: RACK_VERSION=1.4.5
 
+    # https://github.com/oracle/truffleruby/blob/master/doc/user/standalone-distribution.md#testing-truffleruby-in-travisci
+    - name: truffleruby
+      rvm: system
+      before_install:
+        - export TRUFFLERUBY_VERSION=1.0.0-rc8
+        - curl -L https://github.com/oracle/truffleruby/releases/download/vm-$TRUFFLERUBY_VERSION/truffleruby-$TRUFFLERUBY_VERSION-linux-amd64.tar.gz | tar xz
+        - export PATH="$PWD/truffleruby-$TRUFFLERUBY_VERSION-linux-amd64/bin:$PATH"
+        - gem install bundler
+
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head
+    - name: truffleruby
 
 before_install:
   - "gem install bundler"

Gemfile

@@ -12,3 +12,8 @@ gemspec name: 'rackstash'
 group :test do
   gem 'rack', ENV['RACK_VERSION'] ? "~> #{ENV['RACK_VERSION']}" : nil
 end
+
+if RUBY_ENGINE == 'truffleruby'
+  # Truffleruby requires a prerelease of concurrent-ruby currently
+  gem 'concurrent-ruby', '>= 1.1.0.pre2'
+end