Merge pull request #376 from guard/fix_version_constraints

Use .travis.yml to set gem's dependency on Ruby

README.md

@@ -17,7 +17,7 @@ The Listen gem listens to file modifications and notifies you about the changes.
 * You can watch multiple directories.
 * Regexp-patterns for ignoring paths for more accuracy and speed
 * Increased change detection accuracy on OS X HFS and VFAT volumes.
-* Tested on MRI Ruby environments (2.2+ only) via [Travis CI](https://travis-ci.org/guard/listen),
+* Tested on selected Ruby environments via [Travis CI](https://travis-ci.org/guard/listen). (See [.travis.yml](https:///github.com/guard/listen/master/.travis.yml) for supported/tested Ruby Versions),
 
 ## Issues / limitations
 

listen.gemspec

@@ -3,6 +3,29 @@ lib = File.expand_path('../lib', __FILE__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'listen/version'
 
+require 'yaml'
+
+def ruby_version_constraint(filename = '.travis.yml')
+  yaml = YAML.load(IO.read(filename))
+  failable = yaml['matrix']['allow_failures'].map(&:values).flatten
+  versions = yaml['rvm'] - failable
+
+  by_major = versions.map do |x|
+    Gem::Version.new(x).segments[0..2]
+  end.group_by(&:first)
+
+  last_supported_major = by_major.keys.sort.last
+  selected = by_major[last_supported_major].sort.reverse
+
+  lowest = selected.shift
+  current = lowest[1]
+  while( lower = selected.shift)
+    (current -= 1) == lower[1] ? lowest = lower : break
+  end
+
+  ["~> #{lowest[0..1].join('.')}", ">= #{lowest.join('.')}"]
+end
+
 Gem::Specification.new do |s|
   s.name        = 'listen'
   s.version     = Listen::VERSION
@@ -22,7 +45,7 @@ Gem::Specification.new do |s|
   s.executable   = 'listen'
   s.require_path = 'lib'
 
-  s.required_ruby_version = '~> 2.2'
+  s.required_ruby_version = ruby_version_constraint
 
   s.add_dependency 'rb-fsevent', '>= 0.9.3'
   s.add_dependency 'rb-inotify', '>= 0.9.7'