Fixes #2578, check that `installed` isn't empty

The underlying issue in #2578 is when a formula is `keg_only`, but not
installed, we're sending `#last` to an empty Array, which returns
`nil`, and causes the `NoMethodError` reported in #2578 and in the
homebrew cookbook issue. This should also resolve that issue:

https://github.com/opscode-cookbooks/homebrew/issues/53

2 files changed, 35 insertions, 1 deletions

diff --git a/lib/chef/provider/package/homebrew.rb b/lib/chef/provider/package/homebrew.rb
index 822f4c8a42..1b407a1901 100644
--- a/lib/chef/provider/package/homebrew.rb
+++ b/lib/chef/provider/package/homebrew.rb
@@ -94,7 +94,15 @@ class Chef
         # that brew thinks is linked as the current version.
         #
         def current_installed_version
-          brew_info['keg_only'] ? brew_info['installed'].last['version'] : brew_info['linked_keg']
+          if brew_info['keg_only']
+            if brew_info['installed'].empty?
+              nil
+            else
+              brew_info['installed'].last['version']
+            end
+          else
+            brew_info['linked_keg']
+          end
         end
 
         # Packages (formula) available to install should have a
diff --git a/spec/unit/provider/package/homebrew_spec.rb b/spec/unit/provider/package/homebrew_spec.rb
index dccd8edf11..d01d455b09 100644
--- a/spec/unit/provider/package/homebrew_spec.rb
+++ b/spec/unit/provider/package/homebrew_spec.rb
@@ -93,6 +93,27 @@ describe Chef::Provider::Package::Homebrew do
     }
   end
 
+  let(:keg_only_uninstalled_brew_info) do
+    {
+      'name' => 'emacs-kegger',
+      'homepage' => 'http://www.gnu.org/software/emacs/',
+      'versions' => {
+        'stable' => '24.3-keggy',
+        'bottle' => false,
+        'devel' => nil,
+        'head' => 'HEAD'
+      },
+      'revision' => 0,
+      'installed' => [],
+      'linked_keg' => nil,
+      'keg_only' => true,
+      'dependencies' => [],
+      'conflicts_with' => [],
+      'caveats' => '',
+      'options' => []
+    }
+  end
+
   before(:each) do
 
   end
@@ -141,6 +162,11 @@ describe Chef::Provider::Package::Homebrew do
       allow(provider).to receive(:brew_info).and_return(uninstalled_brew_info)
       expect(provider.current_installed_version).to be_nil
     end
+
+    it 'returns nil if the package is keg only and not installed' do
+      allow(provider).to receive(:brew_info).and_return(keg_only_uninstalled_brew_info)
+      expect(provider.current_installed_version).to be_nil
+    end
   end
 
   describe 'brew' do