Git: Added ability to update to a specific tree-ish

2 files changed, 73 insertions, 13 deletions

diff --git a/doc/server/plugins/version/git.txt b/doc/server/plugins/version/git.txt
index b3c469d6c..3f7ab9d9b 100644
--- a/doc/server/plugins/version/git.txt
+++ b/doc/server/plugins/version/git.txt
@@ -20,9 +20,38 @@ it will include the current repository revision in the
 reports/statistics.
 
 Additionally, if the ``GitPython`` library is installed, the Git
-plugin exposes an additional XML-RPC method call, ``Git.Update``,
-which updates the working copy to the latest version in the remote
-origin.
+plugin exposes an additional XML-RPC method call, ``Git.Update``.
+With no arguments, ``Git.Update`` updates the working copy to the
+latest version in the remote tracking branch.  If the current working
+copy doesn't have a remote tracking branch, then nothing is done.
+
+``Git.Update`` can also be given a single argument, the name of a git
+tree-ish (branch, tag, ref, commit, etc.) to check out.  When this is
+done, the new working is updated as well.
+
+For example::
+
+    bcfg2-admin xcmd Git.Update master
+
+This checks out the ``master`` branch and updates it to the latest
+data from the remote ``master`` (if applicable).  If you then run::
+
+    bcfg2-admin xcmd Git.Update
+
+This updates to the latest remote data without changing branches.
+Then::
+
+    bcfg2-admin xcmd Git.Update dd0bb776c
+
+This checks out the specified commit.  Subsequently::
+
+    bcfg2-admin xcmd Git.Update
+
+This does nothing, because the working copy is now in "detached HEAD"
+state, and there can be no remote tracking branch to update from.
+
+To put it another way, once you tell ``Git.Update`` which tree-ish to
+checkout, it stays on that tree-ish until you tell it otherwise.
 
 Enabling the Git plugin
 =======================
diff --git a/src/lib/Bcfg2/Server/Plugins/Git.py b/src/lib/Bcfg2/Server/Plugins/Git.py
index 61d581009..8cc63a46f 100644
--- a/src/lib/Bcfg2/Server/Plugins/Git.py
+++ b/src/lib/Bcfg2/Server/Plugins/Git.py
@@ -52,17 +52,48 @@ class Git(Bcfg2.Server.Plugin.Version):
             self.logger.error(msg)
             raise Bcfg2.Server.Plugin.PluginExecutionError(msg)
 
-    def Update(self):
+    def Update(self, ref=None):
         """ Git.Update() => True|False
         Update the working copy against the upstream repository
         """
+        self.logger.info("Git: Git.Update(ref='%s')" % ref)
+        self.debug_log("Git: Performing garbage collection on repo at %s" %
+                       self.vcs_root)
         try:
-            self.repo.git.pull("--rebase")
-            self.logger.info("Git repo at %s updated to %s" %
-                             (self.vcs_root, self.get_revision()))
-            return True
-        except:  # pylint: disable=W0702
-            err = sys.exc_info()[1]
-            msg = "Failed to pull from git repository: %s" % err
-            self.logger.error(msg)
-            raise Bcfg2.Server.Plugin.PluginExecutionError(msg)
+            self.repo.git.gc('--auto')
+        except git.GitCommandError:
+            self.logger.warning("Git: Failed to perform garbage collection: %s"
+                                % sys.exc_info()[1])
+
+        if ref:
+            self.debug_log("Git: Checking out %s" % ref)
+            try:
+                self.repo.git.checkout('-f', ref)
+            except git.GitCommandError:
+                err = sys.exc_info()[1]
+                msg = "Git: Failed to checkout %s: %s" % (ref, err)
+                self.logger.error(msg)
+                raise Bcfg2.Server.Plugin.PluginExecutionError(msg)
+
+        # determine if we should try to pull to get the latest commit
+        # on this head
+        tracking = None
+        if not self.repo.head.is_detached:
+            self.debug_log("Git: Determining if %s is a tracking branch" %
+                           self.repo.head.ref.name)
+            tracking = self.repo.head.ref.tracking_branch()
+
+        if tracking is not None:
+            self.debug_log("Git: %s is a tracking branch, pulling from %s" %
+                           (self.repo.head.ref.name, tracking))
+            try:
+                self.repo.git.pull("--rebase")
+            except:  # pylint: disable=W0702
+                err = sys.exc_info()[1]
+                msg = "Git: Failed to pull from upstream: %s" % err
+                self.logger.error(msg)
+                raise Bcfg2.Server.Plugin.PluginExecutionError(msg)
+
+        self.logger.info("Git: Repo at %s updated to %s" %
+                         (self.vcs_root, self.get_revision()))
+        return True