Ensure that cherry-picker doesn't exit with bad state on branch clean…

…up (#61)

* Check out previous branch rather than default branch on cleanup

* Add tests

cherry_picker/cherry_picker.py

@@ -38,6 +38,9 @@
     CHECKING_OUT_DEFAULT_BRANCH
     CHECKED_OUT_DEFAULT_BRANCH
 
+    CHECKING_OUT_PREVIOUS_BRANCH
+    CHECKED_OUT_PREVIOUS_BRANCH
+
     PUSHING_TO_REMOTE
     PUSHED_TO_REMOTE
     PUSHING_TO_REMOTE_FAILED
@@ -138,6 +141,11 @@ def set_paused_state(self):
             save_cfg_vals_to_git_cfg(config_path=self.chosen_config_path)
         set_state(WORKFLOW_STATES.BACKPORT_PAUSED)
 
+    def remember_previous_branch(self):
+        """Save the current branch into Git config to be able to get back to it later."""
+        current_branch = get_current_branch()
+        save_cfg_vals_to_git_cfg(previous_branch=current_branch)
+
     @property
     def upstream(self):
         """Get the remote name to use for upstream branches
@@ -184,24 +192,29 @@ def run_cmd(self, cmd):
         output = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
         return output.decode("utf-8")
 
-    def checkout_branch(self, branch_name):
-        """git checkout -b <branch_name>"""
-        cmd = [
-            "git",
-            "checkout",
-            "-b",
-            self.get_cherry_pick_branch(branch_name),
-            f"{self.upstream}/{branch_name}",
-        ]
+    def checkout_branch(self, branch_name, *, create_branch=False):
+        """git checkout [-b] <branch_name>"""
+        if create_branch:
+            checked_out_branch = self.get_cherry_pick_branch(branch_name)
+            cmd = [
+                "git",
+                "checkout",
+                "-b",
+                checked_out_branch,
+                f"{self.upstream}/{branch_name}",
+            ]
+        else:
+            checked_out_branch = branch_name
+            cmd = ["git", "checkout", branch_name]
         try:
             self.run_cmd(cmd)
         except subprocess.CalledProcessError as err:
             click.echo(
-                f"Error checking out the branch {self.get_cherry_pick_branch(branch_name)}."
+                f"Error checking out the branch {branch_name}."
             )
             click.echo(err.output)
             raise BranchCheckoutException(
-                f"Error checking out the branch {self.get_cherry_pick_branch(branch_name)}."
+                f"Error checking out the branch {branch_name}."
             )
 
     def get_commit_message(self, commit_sha):
@@ -225,11 +238,23 @@ def checkout_default_branch(self):
         """git checkout default branch"""
         set_state(WORKFLOW_STATES.CHECKING_OUT_DEFAULT_BRANCH)
 
-        cmd = "git", "checkout", self.config["default_branch"]
-        self.run_cmd(cmd)
+        self.checkout_branch(self.config["default_branch"])
 
         set_state(WORKFLOW_STATES.CHECKED_OUT_DEFAULT_BRANCH)
 
+    def checkout_previous_branch(self):
+        """git checkout previous branch"""
+        set_state(WORKFLOW_STATES.CHECKING_OUT_PREVIOUS_BRANCH)
+
+        previous_branch = load_val_from_git_cfg("previous_branch")
+        if previous_branch is None:
+            self.checkout_default_branch()
+            return
+
+        self.checkout_branch(previous_branch)
+
+        set_state(WORKFLOW_STATES.CHECKED_OUT_PREVIOUS_BRANCH)
+
     def status(self):
         """
         git status
@@ -363,7 +388,12 @@ def cleanup_branch(self, branch):
         Switch to the default branch before that.
         """
         set_state(WORKFLOW_STATES.REMOVING_BACKPORT_BRANCH)
-        self.checkout_default_branch()
+        try:
+            self.checkout_previous_branch()
+        except BranchCheckoutException:
+            click.echo(f"branch {branch} NOT deleted.")
+            set_state(WORKFLOW_STATES.REMOVING_BACKPORT_BRANCH_FAILED)
+            return
         try:
             self.delete_branch(branch)
         except subprocess.CalledProcessError:
@@ -378,14 +408,15 @@ def backport(self):
             raise click.UsageError("At least one branch must be specified.")
         set_state(WORKFLOW_STATES.BACKPORT_STARTING)
         self.fetch_upstream()
+        self.remember_previous_branch()
 
         set_state(WORKFLOW_STATES.BACKPORT_LOOPING)
         for maint_branch in self.sorted_branches:
             set_state(WORKFLOW_STATES.BACKPORT_LOOP_START)
             click.echo(f"Now backporting '{self.commit_sha1}' into '{maint_branch}'")
 
             cherry_pick_branch = self.get_cherry_pick_branch(maint_branch)
-            self.checkout_branch(maint_branch)
+            self.checkout_branch(maint_branch, create_branch=True)
             commit_message = ""
             try:
                 self.cherry_pick()
@@ -419,6 +450,7 @@ def backport(self):
                     self.set_paused_state()
                     return  # to preserve the correct state
             set_state(WORKFLOW_STATES.BACKPORT_LOOP_END)
+        reset_stored_previous_branch()
         reset_state()
 
     def abort_cherry_pick(self):
@@ -440,6 +472,7 @@ def abort_cherry_pick(self):
         if get_current_branch().startswith("backport-"):
             self.cleanup_branch(get_current_branch())
 
+        reset_stored_previous_branch()
         reset_stored_config_ref()
         reset_state()
 
@@ -499,6 +532,7 @@ def continue_cherry_pick(self):
             )
             set_state(WORKFLOW_STATES.CONTINUATION_FAILED)
 
+        reset_stored_previous_branch()
         reset_stored_config_ref()
         reset_state()
 
@@ -828,6 +862,11 @@ def reset_stored_config_ref():
         """Config file pointer is not stored in Git config."""
 
 
+def reset_stored_previous_branch():
+    """Remove the previous branch information from Git config."""
+    wipe_cfg_vals_from_git_cfg("previous_branch")
+
+
 def reset_state():
     """Remove the progress state from Git config."""
     wipe_cfg_vals_from_git_cfg("state")

cherry_picker/test_cherry_picker.py

@@ -84,6 +84,14 @@ def git_commit():
     )
 
 
+@pytest.fixture
+def git_worktree():
+    git_worktree_cmd = "git", "worktree"
+    return lambda *extra_args: (
+        subprocess.run(git_worktree_cmd + extra_args, check=True)
+    )
+
+
 @pytest.fixture
 def git_cherry_pick():
     git_cherry_pick_cmd = "git", "cherry-pick"
@@ -100,12 +108,13 @@ def git_config():
 
 @pytest.fixture
 def tmp_git_repo_dir(tmpdir, cd, git_init, git_commit, git_config):
-    cd(tmpdir)
+    repo_dir = tmpdir.mkdir("tmp-git-repo")
+    cd(repo_dir)
     git_init()
     git_config("--local", "user.name", "Monty Python")
     git_config("--local", "user.email", "[email protected]")
     git_commit("Initial commit", "--allow-empty")
-    yield tmpdir
+    yield repo_dir
 
 
 @mock.patch("subprocess.check_output")
@@ -545,13 +554,19 @@ def test_paused_flow(tmp_git_repo_dir, git_add, git_commit):
             WORKFLOW_STATES.CHECKING_OUT_DEFAULT_BRANCH,
             WORKFLOW_STATES.CHECKED_OUT_DEFAULT_BRANCH,
         ),
+        (
+            "checkout_previous_branch",
+            WORKFLOW_STATES.CHECKING_OUT_PREVIOUS_BRANCH,
+            WORKFLOW_STATES.CHECKED_OUT_PREVIOUS_BRANCH,
+        ),
     ),
 )
 def test_start_end_states(method_name, start_state, end_state, tmp_git_repo_dir):
     assert get_state() == WORKFLOW_STATES.UNSET
 
     with mock.patch("cherry_picker.cherry_picker.validate_sha", return_value=True):
         cherry_picker = CherryPicker("origin", "xxx", [])
+    cherry_picker.remember_previous_branch()
     assert get_state() == WORKFLOW_STATES.UNSET
 
     def _fetch(cmd):
@@ -572,6 +587,22 @@ def test_cleanup_branch(tmp_git_repo_dir, git_checkout):
     git_checkout("-b", "some_branch")
     cherry_picker.cleanup_branch("some_branch")
     assert get_state() == WORKFLOW_STATES.REMOVED_BACKPORT_BRANCH
+    assert get_current_branch() == "main"
+
+
+def test_cleanup_branch_checkout_previous_branch(tmp_git_repo_dir, git_checkout, git_worktree):
+    assert get_state() == WORKFLOW_STATES.UNSET
+
+    with mock.patch("cherry_picker.cherry_picker.validate_sha", return_value=True):
+        cherry_picker = CherryPicker("origin", "xxx", [])
+    assert get_state() == WORKFLOW_STATES.UNSET
+
+    git_checkout("-b", "previous_branch")
+    cherry_picker.remember_previous_branch()
+    git_checkout("-b", "some_branch")
+    cherry_picker.cleanup_branch("some_branch")
+    assert get_state() == WORKFLOW_STATES.REMOVED_BACKPORT_BRANCH
+    assert get_current_branch() == "previous_branch"
 
 
 def test_cleanup_branch_fail(tmp_git_repo_dir):
@@ -585,6 +616,19 @@ def test_cleanup_branch_fail(tmp_git_repo_dir):
     assert get_state() == WORKFLOW_STATES.REMOVING_BACKPORT_BRANCH_FAILED
 
 
+def test_cleanup_branch_checkout_fail(tmp_git_repo_dir, tmpdir, git_checkout, git_worktree):
+    assert get_state() == WORKFLOW_STATES.UNSET
+
+    with mock.patch("cherry_picker.cherry_picker.validate_sha", return_value=True):
+        cherry_picker = CherryPicker("origin", "xxx", [])
+    assert get_state() == WORKFLOW_STATES.UNSET
+
+    git_checkout("-b", "some_branch")
+    git_worktree("add", str(tmpdir.mkdir("test-worktree")), "main")
+    cherry_picker.cleanup_branch("some_branch")
+    assert get_state() == WORKFLOW_STATES.REMOVING_BACKPORT_BRANCH_FAILED
+
+
 def test_cherry_pick(tmp_git_repo_dir, git_add, git_branch, git_commit, git_checkout):
     cherry_pick_target_branches = ("3.8",)
     pr_remote = "origin"