4 files changed, 103 insertions, 0 deletions
diff --git a/README_DEVELOPER.markdown b/README_DEVELOPER.markdown
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+++ b/README_DEVELOPER.markdown
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+Puppet Specific Facts
+=====================
+
+Facter is meant to stand alone and apart from Puppet.  However, Facter often
+runs inside Puppet and all custom facts included in the stdlib module will
+almost always be evaluated in the context of Puppet and Facter working
+together.
+
+Still, we don't want to write custom facts that blow up in the users face if
+Puppet is not loaded in memory.  This is often the case if the user run
+`facter` without also supplying the `--puppet` flag.
+
+Ah! But Jeff, the custom fact won't be in the `$LOAD_PATH` unless the user
+supplies `--facter`! You might say...
+
+Not (always) true I say!  If the user happens to have a CWD of
+`<modulepath>/stdlib/lib` then the facts will automatically be evaluated and
+blow up.
+
+In any event, it's pretty easy to write a fact that has no value if Puppet is
+not loaded.  Simply do it like this:
+
+    Facter.add(:node_vardir) do
+      setcode do
+        # This will be nil if Puppet is not available.
+        Facter::Util::PuppetSettings.with_puppet do
+          Puppet[:vardir]
+        end
+      end
+    end
+
+The `Facter::Util::PuppetSettings.with_puppet` method accepts a block and
+yields to it only if the Puppet library is loaded.  If the Puppet library is
+not loaded, then the method silently returns `nil` which Facter interprets as
+an undefined fact value.  The net effect is that the fact won't be set.
diff --git a/lib/facter/puppet_vardir.rb b/lib/facter/puppet_vardir.rb
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+++ b/lib/facter/puppet_vardir.rb
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+# This facter fact returns the value of the Puppet vardir setting for the node
+# running puppet or puppet agent.  The intent is to enable Puppet modules to
+# automatically have insight into a place where they can place variable data,
+# regardless of the node's platform.
+#
+# The value should be directly usable in a File resource path attribute.
+require 'facter/util/puppet_settings'
+
+Facter.add(:puppet_vardir) do
+  setcode do
+    # This will be nil if Puppet is not available.
+    Facter::Util::PuppetSettings.with_puppet do
+      Puppet[:vardir]
+    end
+  end
+end
diff --git a/lib/facter/util/puppet_settings.rb b/lib/facter/util/puppet_settings.rb
new file mode 100644
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+++ b/lib/facter/util/puppet_settings.rb
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+module Facter
+  module Util
+    module PuppetSettings
+      class << self
+        def with_puppet
+          begin
+            Module.const_get("Puppet")
+          rescue NameError
+            nil
+          else
+            yield
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/unit/facter/util/puppet_settings_spec.rb b/spec/unit/facter/util/puppet_settings_spec.rb
new file mode 100644
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+++ b/spec/unit/facter/util/puppet_settings_spec.rb
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+require 'spec_helper'
+require 'facter/util/puppet_settings'
+
+describe Facter::Util::PuppetSettings do
+
+  describe "#with_puppet" do
+    context "Without Puppet loaded" do
+      before(:each) do
+        Module.expects(:const_get).with("Puppet").raises(NameError)
+      end
+
+      it 'should be nil' do
+        subject.with_puppet { Puppet[:vardir] }.should be_nil
+      end
+      it 'should not yield to the block' do
+        Puppet.expects(:[]).never
+        subject.with_puppet { Puppet[:vardir] }.should be_nil
+      end
+    end
+    context "With Puppet loaded" do
+      module Puppet; end
+      let(:vardir) { "/var/lib/puppet" }
+
+      before :each do
+        Puppet.expects(:[]).with(:vardir).returns vardir
+      end
+      it 'should yield to the block' do
+        subject.with_puppet { Puppet[:vardir] }
+      end
+      it 'should return the nodes vardir' do
+        subject.with_puppet { Puppet[:vardir] }.should eq vardir
+      end
+    end
+  end
+end