feat: swap to making a new feature branch in demo rather than working from develop always

Author: 56kyle

scripts/update-demo.py

@@ -7,7 +7,11 @@
 import typer
 from cookiecutter.utils import work_in
 
+from util import is_ancestor
+from util import get_current_branch
+from util import get_current_commit
 from util import get_demo_name
+from util import get_last_cruft_update_commit
 from util import git
 from util import FolderOption
 from util import REPO_FOLDER
@@ -24,13 +28,28 @@ def update_demo(
 ) -> None:
     """Runs precommit in a generated project and matches the template to the results."""
     try:
-        develop_branch: str = os.getenv("COOKIECUTTER_ROBUST_PYTHON_DEVELOP_BRANCH", "develop")
         demo_name: str = get_demo_name(add_rust_extension=add_rust_extension)
         demo_path: Path = demos_cache_folder / demo_name
+        develop_branch: str = os.getenv("COOKIECUTTER_ROBUST_PYTHON_DEVELOP_BRANCH", "develop")
+
+        current_branch: str = get_current_branch()
+        current_commit: str = get_current_commit()
+
+        _validate_is_feature_branch(branch=current_branch)
+
         typer.secho(f"Updating demo project at {demo_path=}.", fg="yellow")
         with work_in(demo_path):
             require_clean_and_up_to_date_repo()
             git("checkout", develop_branch)
+
+            last_update_commit: str = get_last_cruft_update_commit(demo_path=demo_path)
+            if not is_ancestor(last_update_commit, current_commit):
+                raise ValueError(
+                    f"The last update commit '{last_update_commit}' is not an ancestor of the current commit "
+                    f"'{current_commit}'."
+                )
+
+            git("checkout", "-b", current_branch)
             cruft.update(
                 project_dir=demo_path,
                 template_path=REPO_FOLDER,
@@ -45,5 +64,11 @@ def update_demo(
         sys.exit(1)
 
 
+def _validate_is_feature_branch(branch: str) -> None:
+    """Validates that the cookiecutter has a feature branch checked out."""
+    if not branch.startswith("feature/"):
+        raise ValueError(f"Received branch '{branch}' is not a feature branch.")
+
+
 if __name__ == '__main__':
     cli()

scripts/util.py

@@ -1,4 +1,5 @@
 """Module containing utility functions used throughout cookiecutter_robust_python scripts."""
+import json
 import os
 import shutil
 import stat
@@ -17,6 +18,8 @@
 import cruft
 import typer
 from cookiecutter.utils import work_in
+from cruft._commands.utils.cruft import get_cruft_file
+from cruft._commands.utils.cruft import json_dumps
 from dotenv import load_dotenv
 from typer.models import OptionInfo
 
@@ -106,7 +109,34 @@ def is_branch_synced_with_remote(branch: str) -> bool:
 
 def is_ancestor(ancestor: str, descendent: str) -> bool:
     """Checks if the branch is synced with its remote."""
-    return git("merge-base", "--is-ancestor", ancestor, descendent).returncode == 0
+    return git("merge-base", "--is-ancestor", ancestor, descendent, ignore_error=True) is not None
+
+
+def get_current_branch() -> str:
+    """Returns the current branch name."""
+    return git("branch", "--show-current").stdout.strip()
+
+
+def get_current_commit() -> str:
+    """Returns the current commit reference."""
+    return git("rev-parse", "HEAD").stdout.strip()
+
+
+def get_last_cruft_update_commit(demo_path: Path) -> str:
+    """Returns the commit id for the last time cruft update was ran."""
+    existing_cruft_config: dict[str, Any] = _read_cruft_file(demo_path)
+    last_cookiecutter_commit: Optional[str] = existing_cruft_config.get("commit", None)
+    if last_cookiecutter_commit is None:
+        raise ValueError("Could not find last commit id used to generate demo.")
+    return last_cookiecutter_commit
+
+
+def _read_cruft_file(project_path: Path) -> dict[str, Any]:
+    """Reads the cruft file for the project path provided and returns the results."""
+    cruft_path: Path = get_cruft_file(project_dir_path=project_path)
+    cruft_text: str = cruft_path.read_text()
+    cruft_config: dict[str, Any] = json.loads(cruft_text)
+    return cruft_config
 
 
 @contextmanager