Refactor infra git libs and testing.

infra/libs/git2/ref.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+from infra.libs.git2.util import CalledProcessError
+from infra.libs.git2.util import INVALID
+
+class Ref(object):
+  """Represents a single simple ref in a git Repo."""
+  def __init__(self, repo, ref_str):
+    """
+    @type repo: Repo
+    @type ref_str: str
+    """
+    self._repo = repo
+    self._ref = ref_str
+
+  # Comparison & Representation
+  def __eq__(self, other):
+    return (self is other) or (
+        isinstance(other, Ref) and (
+            self.ref == other.ref and
+            self.repo is other.repo
+        )
+    )
+
+  def __ne__(self, other):
+    return not (self == other)
+
+  def __repr__(self):
+    return 'Ref({_repo!r}, {_ref!r})'.format(**self.__dict__)
+
+  # Accessors
+  # pylint: disable=W0212
+  repo = property(lambda self: self._repo)
+  ref = property(lambda self: self._ref)
+
+  # Properties
+  @property
+  def commit(self):
+    """Get the Commit at the tip of this Ref."""
+    try:
+      val = self._repo.run('show-ref', '--verify', self._ref)
+    except CalledProcessError:
+      return INVALID
+    return self._repo.get_commit(val.split()[0])
+
+  # Methods
+  def to(self, other):
+    """Generate Commit()'s which occur from `self..other`."""
+    assert self.commit is not INVALID
+    arg = '%s..%s' % (self.ref, other.ref)
+    for hsh in self.repo.run('rev-list', '--reverse', arg).splitlines():
+      yield self.repo.get_commit(hsh)
+
+  def fast_forward_push(self, commit):
+    """Push |commit| to this ref on the remote, and update the local copy of the
+    ref to |commit|."""
+    self.repo.run('push', 'origin', '%s:%s' % (commit.hsh, self.ref))
+    self.update_to(commit)
+
+  def update_to(self, commit):
+    """Update the local copy of the ref to |commit|."""
+    self.repo.run('update-ref', self.ref, commit.hsh)