Add a custom fact for rabbitmq's plugins folder

If you want to add third party plugins with puppet you need to know
where the plugins folder is located.
This can differ depending on rabbitmq version or OS.

lib/facter/rabbitmq_plugins_dirs.rb

@@ -0,0 +1,9 @@
+Facter.add(:rabbitmq_plugins_dirs) do
+  setcode do
+    if Facter::Util::Resolution.which('rabbitmqctl')
+      rabbitmq_pluginsdirs_env = Facter::Core::Execution.execute("rabbitmqctl eval 'application:get_env(rabbit, plugins_dir).'")
+      rabbitmq_plugins_dirs = %r{^\{ok\,\"(\/.+\/\w+)}.match(rabbitmq_pluginsdirs_env)[1]
+      rabbitmq_plugins_dirs.split(':')
+    end
+  end
+end

spec/unit/facter/util/fact_rabbitmq_plugins_dirs_spec.rb

@@ -0,0 +1,39 @@
+require 'spec_helper'
+
+describe Facter::Util::Fact do
+  before { Facter.clear }
+
+  describe 'rabbitmq_plugins_dirs' do
+    context 'with multiple plugins dirs' do
+      it do
+        Facter::Util::Resolution.expects(:which).with('rabbitmqctl').returns(true)
+        Facter::Core::Execution.expects(:execute).with("rabbitmqctl eval 'application:get_env(rabbit, plugins_dir).'").returns('{ok,"/usr/lib/rabbitmq/plugins:/usr/lib/rabbitmq/lib/rabbitmq_server-3.7.10/plugins"}')
+        expect(Facter.fact(:rabbitmq_plugins_dirs).value).to match_array(
+          [
+            '/usr/lib/rabbitmq/plugins',
+            '/usr/lib/rabbitmq/lib/rabbitmq_server-3.7.10/plugins'
+          ]
+        )
+      end
+    end
+
+    context 'with only 1 plugins dir' do
+      it do
+        Facter::Util::Resolution.expects(:which).with('rabbitmqctl').returns(true)
+        Facter::Core::Execution.expects(:execute).with("rabbitmqctl eval 'application:get_env(rabbit, plugins_dir).'").returns('{ok,"/usr/lib/rabbitmq/lib/rabbitmq_server-0.0.0/plugins"}')
+        expect(Facter.fact(:rabbitmq_plugins_dirs).value).to match_array(
+          [
+            '/usr/lib/rabbitmq/lib/rabbitmq_server-0.0.0/plugins'
+          ]
+        )
+      end
+    end
+
+    context 'rabbitmqctl is not in path' do
+      it do
+        Facter::Util::Resolution.expects(:which).with('rabbitmqctl').returns(false)
+        expect(Facter.fact(:rabbitmq_plugins_dirs).value).to be_nil
+      end
+    end
+  end
+end