Add repo start option to create the branch based off HEAD

This makes it way easier to recover from forgetting to run repo start
before committing: just run `repo start -b new-branch`, instead of
all that tedious mucking around with reflogs.

Change-Id: I56d49dce5d027e28fbba0507ac10cd763ccfc36d
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/232712
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/project.py b/project.py
index 8212e0c0..4076bc5d 100755
--- a/project.py
+++ b/project.py
@@ -1697,7 +1697,7 @@ class Project(object):
 
 # Branch Management ##
 
-  def StartBranch(self, name, branch_merge=''):
+  def StartBranch(self, name, branch_merge='', revision=None):
     """Create a new branch off the manifest's revision.
     """
     if not branch_merge:
@@ -1718,7 +1718,11 @@ class Project(object):
     branch.merge = branch_merge
     if not branch.merge.startswith('refs/') and not ID_RE.match(branch_merge):
       branch.merge = R_HEADS + branch_merge
-    revid = self.GetRevisionId(all_refs)
+
+    if revision is None:
+      revid = self.GetRevisionId(all_refs)
+    else:
+      revid = self.work_git.rev_parse(revision)
 
     if head.startswith(R_HEADS):
       try: