fix git provider checkout of a remote ref on an existing repo

Per discussion of https://github.com/puppetlabs/puppetlabs-vcsrepo/issues/51 in
the git channel on freenode, EugeneKay <eugene@kashpureff.org> stated that `git
rev-parse` is not capable of inspecting remote refs but that `git ls-remote`
is.  This patch makes a second attempt to resolve the ref with `ls-remote` if
`rev-parse` fails.

The git provider also appears to support several type features that are not
tagged under `has_features`.  It's not clear if this is the best way to resolve
this issue or if the provider should be refactored to work with different type
features.

Demonstration of the problem with changing refs (branches and tags)

    $ git --version
    git version 1.7.1
    $ cat master.pp branch.pp
      vcsrepo { '/tmp/vcsrepo':
        ensure    => present,
        provider  => git,
        source    => 'https://github.com/puppetlabs/puppetlabs-vcsrepo.git',
        revision  => 'master',
      }
      vcsrepo { '/tmp/vcsrepo':
        ensure    => present,
        provider  => git,
        source    => 'https://github.com/puppetlabs/puppetlabs-vcsrepo.git',
        revision  => 'feature/cvs',
      }
    $ puppet apply --modulepath=`pwd`/.. master.pp
    Notice: /Stage[main]//Vcsrepo[/tmp/vcsrepo]/ensure: Creating repository from present
    Notice: /Stage[main]//Vcsrepo[/tmp/vcsrepo]/ensure: created
    Notice: Finished catalog run in 2.19 seconds
    $ puppet apply --modulepath=`pwd`/.. branch.pp
    Error: /Stage[main]//Vcsrepo[/tmp/vcsrepo]: Could not evaluate: Execution of '/usr/bin/git rev-parse feature/cvs' returned 128: fatal: ambiguous argument 'feature/cvs': unknown revision or path not in the working tree.
    Use '--' to separate paths from revisions
    feature/cvs

    Notice: Finished catalog run in 1.69 seconds

1 files changed, 27 insertions, 3 deletions

diff --git a/spec/unit/puppet/provider/vcsrepo/git_spec.rb b/spec/unit/puppet/provider/vcsrepo/git_spec.rb
index cb6c0c6..e10fd1e 100644
--- a/spec/unit/puppet/provider/vcsrepo/git_spec.rb
+++ b/spec/unit/puppet/provider/vcsrepo/git_spec.rb
@@ -132,7 +132,7 @@ describe_provider :vcsrepo, :git, :resource => {:path => '/tmp/vcsrepo'} do
           provider.expects(:git).with('config', 'remote.origin.url').returns('')
           provider.expects(:git).with('fetch', 'origin') # FIXME
           provider.expects(:git).with('fetch', '--tags', 'origin')
-          provider.expects(:git).with('rev-parse', resource.value(:revision)).returns('currentsha')
+          provider.expects(:git).with('rev-parse', '--revs-only', resource.value(:revision)).returns('currentsha')
           provider.expects(:git).with('tag', '-l').returns("Hello")
           provider.revision.should == resource.value(:revision)
         end
@@ -143,12 +143,36 @@ describe_provider :vcsrepo, :git, :resource => {:path => '/tmp/vcsrepo'} do
           provider.expects(:git).with('config', 'remote.origin.url').returns('')
           provider.expects(:git).with('fetch', 'origin') # FIXME
           provider.expects(:git).with('fetch', '--tags', 'origin')
-          provider.expects(:git).with('rev-parse', resource.value(:revision)).returns('othersha')
+          provider.expects(:git).with('rev-parse', '--revs-only', resource.value(:revision)).returns('othersha')
           provider.expects(:git).with('tag', '-l').returns("Hello")
           provider.revision.should == 'currentsha'
         end
       end
 
+      context "when its a ref to a remote head" do
+        it "should return the revision" do
+          provider.expects(:git).with('config', 'remote.origin.url').returns('')
+          provider.expects(:git).with('fetch', 'origin') # FIXME
+          provider.expects(:git).with('fetch', '--tags', 'origin')
+          provider.expects(:git).with('tag', '-l').returns("Hello")
+          provider.expects(:git).with('rev-parse', '--revs-only', resource.value(:revision)).returns('')
+          provider.expects(:git).with('ls-remote', '--heads', '--tags', 'origin', resource.value(:revision)).returns("newsha refs/heads/#{resource.value(:revision)}")
+          provider.revision.should == 'currentsha'
+        end
+      end
+
+      context "when its a ref to non existant remote head" do
+        it "should fail" do
+          provider.expects(:git).with('config', 'remote.origin.url').returns('')
+          provider.expects(:git).with('fetch', 'origin') # FIXME
+          provider.expects(:git).with('fetch', '--tags', 'origin')
+          provider.expects(:git).with('tag', '-l').returns("Hello")
+          provider.expects(:git).with('rev-parse', '--revs-only', resource.value(:revision)).returns('')
+          provider.expects(:git).with('ls-remote', '--heads', '--tags', 'origin', resource.value(:revision)).returns('')
+          expect { provider.revision }.should raise_error(Puppet::Error, /not a local or remote ref$/)
+        end
+      end
+
       context "when the source is modified" do
         resource_with :source => 'git://git@foo.com/bar.git' do
           it "should update the origin url" do
@@ -156,7 +180,7 @@ describe_provider :vcsrepo, :git, :resource => {:path => '/tmp/vcsrepo'} do
             provider.expects(:git).with('config', 'remote.origin.url', 'git://git@foo.com/bar.git')
             provider.expects(:git).with('fetch', 'origin') # FIXME
             provider.expects(:git).with('fetch', '--tags', 'origin')
-            provider.expects(:git).with('rev-parse', resource.value(:revision)).returns('currentsha')
+            provider.expects(:git).with('rev-parse', '--revs-only', resource.value(:revision)).returns('currentsha')
             provider.expects(:git).with('tag', '-l').returns("Hello")
             provider.revision.should == resource.value(:revision)
           end