git: Don't reset last active branch to wrong commit

When we change the checked out code using `git reset --hard <rev>` we
also change the revision that the currently active branch points to.
This leads to that branch pointing to a wrong commit as we're actually
checking out a different branch (we switch to it just a little bit
later). Instead of modifying the current branch we should just modify
the working copy, which can be done by `git checkout -f <rev>`.

master/buildbot/newsfragments/git-step-correct-branch-commits.bugfix

@@ -0,0 +1,2 @@
+Fixed the ``Git`` source step causing last active branch to point to wrong commits.
+This only affected the branch state in the repository, the checked out code was correct.

master/buildbot/steps/source/git.py

@@ -332,7 +332,7 @@ def _fetch(self, _):
  rev = self.revision
  else:
  rev = 'FETCH_HEAD'
- command = ['reset', '--hard', rev, '--']
+ command = ['checkout', '-f', rev]
  abandonOnFailure = not self.retryFetch and not self.clobberOnFailure
  res = yield self._dovccmd(command, abandonOnFailure)
 
@@ -424,9 +424,8 @@ def _fullClone(self, shallowClone=False):
 
  # If revision specified checkout that revision
  if self.revision:
- res = yield self._dovccmd(['reset', '--hard',
- self.revision, '--'],
- shallowClone)
+ res = yield self._dovccmd(['checkout', '-f', self.revision], shallowClone)
+
  # init and update submodules, recursively. If there's not recursion
  # it will not do it.
  if self.submodules:

master/buildbot/test/unit/steps/test_source_gerrit.py

@@ -64,7 +64,7 @@ def test_mode_full_clean(self):
  'gerrit_branch', '--progress'])
  + 0,
  ExpectShell(workdir='wkdir',
- command=['git', 'reset', '--hard', 'FETCH_HEAD', '--'])
+ command=['git', 'checkout', '-f', 'FETCH_HEAD'])
  + 0,
  ExpectShell(workdir='wkdir',
  command=['git', 'checkout', '-B', 'gerrit_branch'])
@@ -110,7 +110,7 @@ def test_mode_full_clean_force_build(self):
  'refs/changes/34/1234/567', '--progress'])
  + 0,
  ExpectShell(workdir='wkdir',
- command=['git', 'reset', '--hard', 'FETCH_HEAD', '--'])
+ command=['git', 'checkout', '-f', 'FETCH_HEAD'])
  + 0,
  ExpectShell(workdir='wkdir',
  command=['git', 'checkout', '-B', 'refs/changes/34/1234/567'])
@@ -156,7 +156,7 @@ def test_mode_full_clean_force_same_project(self):
  'refs/changes/34/1234/567', '--progress'])
  + 0,
  ExpectShell(workdir='wkdir',
- command=['git', 'reset', '--hard', 'FETCH_HEAD', '--'])
+ command=['git', 'checkout', '-f', 'FETCH_HEAD'])
  + 0,
  ExpectShell(workdir='wkdir',
  command=['git', 'checkout', '-B', 'refs/changes/34/1234/567'])
@@ -202,7 +202,7 @@ def test_mode_full_clean_different_project(self):
  'HEAD', '--progress'])
  + 0,
  ExpectShell(workdir='wkdir',
- command=['git', 'reset', '--hard', 'FETCH_HEAD', '--'])
+ command=['git', 'checkout', '-f', 'FETCH_HEAD'])
  + 0,
  ExpectShell(workdir='wkdir',
  command=['git', 'rev-parse', 'HEAD'])