Add pre-commit try-repo

`try-repo` is useful for:
- Trying out a remote hook repository without needing to configure it.
- Testing a hook repository while developing it.

pre_commit/commands/try_repo.py

@@ -0,0 +1,44 @@
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import collections
+import os.path
+
+from aspy.yaml import ordered_dump
+
+import pre_commit.constants as C
+from pre_commit import git
+from pre_commit import output
+from pre_commit.commands.run import run
+from pre_commit.manifest import Manifest
+from pre_commit.runner import Runner
+from pre_commit.store import Store
+from pre_commit.util import tmpdir
+
+
+def try_repo(args):
+    ref = args.ref or git.head_sha(args.repo)
+
+    with tmpdir() as tempdir:
+        if args.hook:
+            hooks = [{'id': args.hook}]
+        else:
+            manifest = Manifest(Store(tempdir).clone(args.repo, ref))
+            hooks = [{'id': hook_id} for hook_id in sorted(manifest.hooks)]
+
+        items = (('repo', args.repo), ('sha', ref), ('hooks', hooks))
+        config = {'repos': [collections.OrderedDict(items)]}
+        config_s = ordered_dump(config, **C.YAML_DUMP_KWARGS)
+
+        config_filename = os.path.join(tempdir, C.CONFIG_FILE)
+        with open(config_filename, 'w') as cfg:
+            cfg.write(config_s)
+
+        output.write_line('=' * 79)
+        output.write_line('Using config:')
+        output.write_line('=' * 79)
+        output.write(config_s)
+        output.write_line('=' * 79)
+
+        runner = Runner('.', config_filename, store_dir=tempdir)
+        return run(runner, args)