core: Vagrant.has_plugin? can take version requirements [GH-4650]

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 IMPROVEMENTS:
 
+  - core: `has_plugin?` function now takes a second argument which is a
+      version constraint requirement. [GH-4650]
   - guests/arch: Support predictable network interface naming. [GH-4468]
   - guests/suse: Support NFS client install, rsync setup. [GH-4492]
   - guests/tinycore: Support changing host names. [GH-4469]

lib/vagrant.rb

@@ -141,13 +141,22 @@ module Vagrant
   # This checks if a plugin with the given name is installed. This can
   # be used from the Vagrantfile to easily branch based on plugin
   # availability.
-  def self.has_plugin?(name)
-    # We check the plugin names first because those are cheaper to check
-    return true if plugin("2").manager.registered.any? { |p| p.name == name }
+  def self.has_plugin?(name, version=nil)
+    if !version
+      # We check the plugin names first because those are cheaper to check
+      return true if plugin("2").manager.registered.any? { |p| p.name == name }
+    end
+
+    # Make the requirement object
+    version = Gem::Requirement.new([version]) if version
 
     # Now check the plugin gem names
     require "vagrant/plugin/manager"
-    Plugin::Manager.instance.installed_specs.any? { |s| s.name == name }
+    Plugin::Manager.instance.installed_specs.any? do |s|
+      match = s.name == name
+      next match if !version
+      next version.satisfied_by?(s.version)
+    end
   end
 
   # Returns a superclass to use when creating a plugin for Vagrant.

test/unit/vagrant_test.rb

@@ -74,6 +74,16 @@ describe Vagrant do
       expect(described_class.has_plugin?("foo")).to be_true
       expect(described_class.has_plugin?("bar")).to be_false
     end
+
+    it "finds plugins by gem version" do
+      specs = [Gem::Specification.new]
+      specs[0].name = "foo"
+      specs[0].version = "1.2.3"
+      Vagrant::Plugin::Manager.instance.stub(installed_specs: specs)
+
+      expect(described_class.has_plugin?("foo", "~> 1.2.0")).to be_true
+      expect(described_class.has_plugin?("foo", "~> 1.0.0")).to be_false
+    end
   end
 
   describe "require_version" do