Don't overwrite hooks without --force

Currently, `bark install` silently overwrites any
`reference-transaction` hook that may be present. This is a
potentially very destructive action, so we should take proper care
before doing so.

I don't think there's a good way to automatically resolve the conflict
in case the file already exists, so this implementation simply lists
the conflicting files and leaves it to the user to resolve the
conflict manually. (For example, we could move both hook files into
`hooks/reference-transaction.d/` and make
`hooks/reference-transaction` a script that calls all scripts in
`reference-transaction.d/`, but it's not obvious that things like
order of execution wouldn't matter.)

gitbark/cli/__main__.py

@@ -177,7 +177,15 @@ def protect(ctx):
 
 @cli.command()
 @click.pass_context
-def install(ctx):
+@click.option(
+    "-f",
+    "--force",
+    is_flag=True,
+    show_default=True,
+    default=False,
+    help="Overwrite existing hooks.",
+)
+def install(ctx, force):
     """
     Install GitBark modules in repo.
 
@@ -193,7 +201,7 @@ def install(ctx):
     ensure_bootstrap_verified(project)
 
     try:
-        install_cmd(project)
+        install_cmd(project, force)
         logger.info("Hooks installed successfully")
     except RuleViolation as e:
         pp_violation(e)

gitbark/commands/install.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from ..cli.util import CliFail
 from ..project import Project
 
 import pkg_resources
@@ -22,12 +23,22 @@
 logger = logging.getLogger(__name__)
 
 
-def install(project: Project) -> None:
+def install(project: Project, force: bool) -> None:
     """
     Installs GitBark
     """
-    if not hooks_installed(project):
-        install_hooks(project)
+    hooks_missing = hooks_not_installed(project)
+    if hooks_missing:
+        hooks_conflicting = [hook_path for hook_path in hooks_missing if os.path.exists(hook_path)]
+        if force or not hooks_conflicting:
+            install_hooks(project)
+
+        else:
+            conflict_list = '\n'.join(f'{hook_path}' for hook_path in hooks_conflicting)
+            raise CliFail(
+                'Hooks already exist:\n\n'
+                f'{conflict_list}\n\n'
+                'Please delete them or re-run this command with the --force flag.')
 
 
 def install_hooks(project: Project):
@@ -54,7 +65,7 @@ def make_executable(path: str):
     os.chmod(path, new_permissions)
 
 
-def hooks_installed(project: Project):
+def hooks_not_installed(project: Project) -> list[str]:
     reference_transaction_data = pkg_resources.resource_string(
         __name__, "hooks/reference_transaction"
     ).decode()
@@ -63,10 +74,10 @@ def hooks_installed(project: Project):
     reference_transaction_path = f"{hooks_path}/reference-transaction"
 
     if not os.path.exists(reference_transaction_path):
-        return False
+        return [reference_transaction_path]
 
     with open(reference_transaction_path, "r") as f:
         if not f.read() == reference_transaction_data:
-            return False
+            return [reference_transaction_path]
 
-    return True
+    return []