Make 'git bz add-url' more like git rebase

Instead of resetting the branch and applying the patches there,
move to a detached HEAD, apply patches to the detached HEAD and
then make a single update to the branch ref.

The only real advantage of this is that 'git reflog show <branchname>'
shows a single meaningful commit.

2 files changed, 25 insertions, 21 deletions

diff --git a/TODO b/TODO
index 666a84c..5a2f609 100644
--- a/TODO
+++ b/TODO
@@ -70,19 +70,12 @@ Pass --3way to git-am
 
 Make -u/--add-url kinder on the reflog
 
-  -u works by resetting, then on each patch, running git cherry-pick
-  followed by git commit --amend. It would be nice to only have one
-  (informative) reflog entry for the entire process, or at least avoid
-  the double commits.
+  -u works each patch, running git cherry-pick followed by
+  git commit --amend. It would be nice to only avoid the double
+  commits.
 
   The double commits could be avoided if if we did the 'rewrite patch'
   thing for 'git bz apply'- then we could use it here too and just
   pass the whole sequence to 'git am'.  And by setting
   GIT_REFLOG_ACTION='bz add-url' it should work almost perfectly.
 
-  It wouldn't give a single reflog entry, but 'git rebase' and
-  'git am' don't show up as a single entry either. 'git rebase'
-  does show up as a single entry in 'git reflog show master'; that's
-  done by detaching from the branch during the operation. We could
-  do that as well.
-
diff --git a/git-bz b/git-bz
index c76757d..fc7f6ac 100755
--- a/git-bz
+++ b/git-bz
@@ -1173,18 +1173,23 @@ def add_url(bug, commits):
 
     newer_commits = rev_list_commits(commits[0].id + "..HEAD")
 
-    head_id = newer_commits[0].id if newer_commits else oldest_commit.id
+    orig_head = newer_commits[0].id if newer_commits else commits[0].id
 
     try:
-        print "Resetting to the parent revision"
-        git.reset(oldest_commit.id + "^", hard=True)
+        branch_name = git.symbolic_ref("HEAD", q=True)
+    except CalledProcessError:
+        branch_name = None
+    try:
+        # Detach HEAD from the branch; this gives a cleaner reflog for the branch
+        print "Moving to starting point"
+        git.checkout(oldest_commit.id + "^", q=True)
 
         for commit in reversed(commits):
             if not commit_needs_url(commit, bug.id):
                 print "Recommitting", commit.id[0:7], commit.subject, "(already has bug #)"
                 git.cherry_pick(commit.id)
                 # Find the new commit ID, though it doesn't matter much here
-                commit.id = git.rev_list("HEAD^!")
+                commit.id = git.rev_parse("HEAD")
                 continue
 
             print "Adding bug reference  ", commit.id[0:7], commit.subject
@@ -1194,18 +1199,24 @@ def add_url(bug, commits):
 
             # In this case, we need the new commit ID, so that when we later format the
             # patch, we format the patch with the added bug URL
-            commit.id = git.rev_list("HEAD^!")
+            commit.id = git.rev_parse("HEAD")
 
         for commit in reversed(newer_commits):
             print "Recommitting", commit.id[0:7], commit.subject
             git.cherry_pick(commit.id)
-            commit.id = git.rev_list("HEAD^!")
+            commit.id = git.rev_parse("HEAD")
+
+        new_head = newer_commits[0].id if newer_commits else commits[0].id
+        if branch_name is not None:
+            git.update_ref("-m", "bz add-url: adding references to %s" % bug.get_url(),
+                           branch_name, new_head)
+            git.symbolic_ref("HEAD", branch_name)
     except:
-        traceback.print_exc(None, sys.stderr)
-        print >>sys.stderr
-        print >>sys.stderr, "Something went wrong rewriting commmits to add URLs"
-        print >>sys.stderr, "To restore to the original state: git reset --hard %s" % head_id[0:12]
-        sys.exit(1)
+        print "Cleaning up back to original state on error"
+        git.reset(orig_head, hard=True)
+        if branch_name is not None:
+            git.symbolic_ref("HEAD", branch_name)
+        raise
 
 def do_add_url(bug_reference, commit_or_revision_range):
     commits = get_commits(commit_or_revision_range)