Make install -f / --overwrite work.

pre_commit/commands/install.py

@@ -7,6 +7,7 @@ import os.path
 import pkg_resources
 import stat
 
+
 # This is used to identify the hook file we install
 IDENTIFYING_HASH = 'd8ee923c46731b42cd95cc869add4062'
 
@@ -23,7 +24,7 @@ def make_executable(filename):
     )
 
 
-def install(runner):
+def install(runner, overwrite=False):
     """Install the pre-commit hooks."""
     pre_commit_file = pkg_resources.resource_filename(
         'pre_commit', 'resources/pre-commit-hook',
@@ -34,7 +35,18 @@ def install(runner):
         os.path.exists(runner.pre_commit_path) and
         not is_our_pre_commit(runner.pre_commit_path)
     ):
-        os.rename(runner.pre_commit_path, runner.pre_commit_path + '.legacy')
+        os.rename(runner.pre_commit_path, runner.pre_commit_legacy_path)
+
+    # If we specify overwrite, we simply delete the legacy file
+    if overwrite and os.path.exists(runner.pre_commit_legacy_path):
+        os.remove(runner.pre_commit_legacy_path)
+    elif os.path.exists(runner.pre_commit_legacy_path):
+        print(
+            'Running in migration mode with existing hooks at {0}\n'
+            'Use -f to use only pre-commit.'.format(
+                runner.pre_commit_legacy_path,
+            )
+        )
 
     with open(runner.pre_commit_path, 'w') as pre_commit_file_obj:
         pre_commit_file_obj.write(open(pre_commit_file).read())

pre_commit/main.py

@@ -28,7 +28,13 @@ def main(argv):
 
     subparsers = parser.add_subparsers(dest='command')
 
-    subparsers.add_parser('install', help='Intall the pre-commit script.')
+    install_parser = subparsers.add_parser(
+        'install', help='Intall the pre-commit script.',
+    )
+    install_parser.add_argument(
+        '-f', '--overwrite', action='store_true',
+        help='Overwrite existing hooks / remove migration mode.',
+    )
 
     subparsers.add_parser('uninstall', help='Uninstall the pre-commit script.')
 
@@ -67,7 +73,7 @@ def main(argv):
     runner = Runner.create()
 
     if args.command == 'install':
-        return install(runner)
+        return install(runner, overwrite=args.overwrite)
     elif args.command == 'uninstall':
         return uninstall(runner)
     elif args.command == 'clean':

pre_commit/runner.py

@@ -41,7 +41,14 @@ class Runner(object):
 
     @cached_property
     def pre_commit_path(self):
-        return os.path.join(self.git_root, '.git/hooks/pre-commit')
+        return os.path.join(self.git_root, '.git', 'hooks', 'pre-commit')
+
+    @cached_property
+    def pre_commit_legacy_path(self):
+        """The path in the 'hooks' directory representing the temporary
+        storage for existing pre-commit hooks.
+        """
+        return self.pre_commit_path + '.legacy'
 
     @cached_property
     def cmd_runner(self):