[PATCH b4 v2 32/44] review: clean up a review branch that cannot be finished

create_review_branch() checks the new branch out before building it.
Two of the three failures after that point put the caller back and
delete the branch; the one that cannot read the patch range just
exits. A detached start got no cleanup at all, and the leftover branch
made the next attempt fail with "Branch already exists".

Route all three through one cleanup helper that restores via
git_head_restore_args(), so a detached start has somewhere to go back
to.

Signed-off-by: Christian Brauner (Amutable) <[email protected]>
---
 src/b4/review/_review.py | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/b4/review/_review.py b/src/b4/review/_review.py
index c3aa8e9..5a9f0d1 100644
--- a/src/b4/review/_review.py
+++ b/src/b4/review/_review.py
@@ -283,11 +283,16 @@ def create_review_branch(
         logger.critical('Branch %s already exists', branch_name)
         sys.exit(1)
 
-    # Save current branch for potential restore on error
-    current_branch: Optional[str] = None
-    ecode, out = b4.git_run_command(topdir, ['symbolic-ref', '--short', 'HEAD'])
-    if ecode == 0:
-        current_branch = out.strip()
+    # Save the current position for potential restore on error: everything
+    # past the checkout below runs on the new branch, and git refuses to
+    # delete the branch HEAD is sitting on.
+    restore_head = b4.git_head_restore_args(topdir)
+
+    def drop_half_built_branch() -> None:
+        """Put the caller back and take the unfinished branch with us."""
+        if restore_head:
+            b4.git_run_command(topdir, restore_head, logstderr=True)
+        b4.git_run_command(topdir, ['branch', '-D', branch_name], logstderr=True)
 
     # Resolve base_commit to a concrete hash before checkout changes HEAD
     ecode, out = b4.git_run_command(
@@ -316,10 +321,7 @@ def create_review_branch(
         logger.critical(out.strip())
         # Abort the cherry-pick if in progress
         b4.git_run_command(topdir, ['cherry-pick', '--abort'], logstderr=True)
-        # Restore previous branch
-        if current_branch:
-            b4.git_run_command(topdir, ['checkout', current_branch], logstderr=True)
-        b4.git_run_command(topdir, ['branch', '-D', branch_name], logstderr=True)
+        drop_half_built_branch()
         sys.exit(1)
 
     # Record the first patch commit (the one right after base)
@@ -328,6 +330,9 @@ def create_review_branch(
     )
     if ecode > 0 or not out.strip():
         logger.critical('Unable to determine first patch commit')
+        # HEAD is on a branch that was never finished, as in the other two
+        # post-checkout failures around this one.
+        drop_half_built_branch()
         sys.exit(1)
     all_commits = out.strip().splitlines()
     prereq_commits = all_commits[:num_prereqs]
@@ -420,10 +425,7 @@ def create_review_branch(
     if ecode > 0:
         logger.critical('Unable to create tracking commit')
         logger.critical(out.strip())
-        # Restore previous branch
-        if current_branch:
-            b4.git_run_command(topdir, ['checkout', current_branch], logstderr=True)
-        b4.git_run_command(topdir, ['branch', '-D', branch_name], logstderr=True)
+        drop_half_built_branch()
         sys.exit(1)
 
     # Mark cover + patch messages as Seen in the messages DB

-- 
2.53.0