Teach pre-commit try-repo to clone uncommitted changes

pre_commit/commands/run.py

@@ -199,11 +199,7 @@ def _run_hooks(config, hooks, args, environ):
         retval |= _run_single_hook(filenames, hook, args, skips, cols)
         if retval and config['fail_fast']:
             break
-    if (
-            retval and
-            args.show_diff_on_failure and
-            subprocess.call(('git', 'diff', '--quiet', '--no-ext-diff')) != 0
-    ):
+    if retval and args.show_diff_on_failure and git.has_diff():
         output.write_line('All changes made by hooks:')
         subprocess.call(('git', '--no-pager', 'diff', '--no-ext-diff'))
     return retval

pre_commit/commands/try_repo.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import
 from __future__ import unicode_literals
 
 import collections
+import logging
 import os.path
 
 from aspy.yaml import ordered_dump
@@ -12,23 +13,50 @@ from pre_commit import output
 from pre_commit.clientlib import load_manifest
 from pre_commit.commands.run import run
 from pre_commit.store import Store
+from pre_commit.util import cmd_output
 from pre_commit.util import tmpdir
 
+logger = logging.getLogger(__name__)
+
+
+def _repo_ref(tmpdir, repo, ref):
+    # if `ref` is explicitly passed, use it
+    if ref:
+        return repo, ref
+
+    ref = git.head_rev(repo)
+    # if it exists on disk, we'll try and clone it with the local changes
+    if os.path.exists(repo) and git.has_diff('HEAD', repo=repo):
+        logger.warning('Creating temporary repo with uncommitted changes...')
+
+        shadow = os.path.join(tmpdir, 'shadow-repo')
+        cmd_output('git', 'clone', repo, shadow)
+        cmd_output('git', 'checkout', ref, '-b', '_pc_tmp', cwd=shadow)
+        idx = git.git_path('index', repo=shadow)
+        objs = git.git_path('objects', repo=shadow)
+        env = dict(os.environ, GIT_INDEX_FILE=idx, GIT_OBJECT_DIRECTORY=objs)
+        cmd_output('git', 'add', '-u', cwd=repo, env=env)
+        git.commit(repo=shadow)
+
+        return shadow, git.head_rev(shadow)
+    else:
+        return repo, ref
+
 
 def try_repo(args):
-    ref = args.ref or git.head_rev(args.repo)
-
     with tmpdir() as tempdir:
+        repo, ref = _repo_ref(tempdir, args.repo, args.ref)
+
         store = Store(tempdir)
         if args.hook:
             hooks = [{'id': args.hook}]
         else:
-            repo_path = store.clone(args.repo, ref)
+            repo_path = store.clone(repo, ref)
             manifest = load_manifest(os.path.join(repo_path, C.MANIFEST_FILE))
             manifest = sorted(manifest, key=lambda hook: hook['id'])
             hooks = [{'id': hook['id']} for hook in manifest]
 
-        items = (('repo', args.repo), ('rev', ref), ('hooks', hooks))
+        items = (('repo', repo), ('rev', ref), ('hooks', hooks))
         config = {'repos': [collections.OrderedDict(items)]}
         config_s = ordered_dump(config, **C.YAML_DUMP_KWARGS)