--- a/checker.py	Sun Jul 17 23:42:38 2016 +0800
+++ b/checker.py	Mon Jul 18 14:02:28 2016 +0800
@@ -75,13 +75,21 @@
 
 
 def git_clone(url, dest):
-    return run(['git', 'clone', '--depth', '1', url, dest])
+    return run(['git', 'clone', url, dest])
 
 
 def hg_clone(url, dest):
     return run(['hg', 'clone', url, dest])
 
 
+def git_checkout(commit):
+    return run(['git', 'checkout', commit])
+
+
+def hg_update(commit):
+    return run(['hg', 'update', commit])
+
+
 def git_status():
     return run(['git', 'status'])
 
@@ -131,7 +139,7 @@
     return files
 
 
-def execute(tmp, config):
+def execute(tmp, config, args):
     if not prevalidate(config):
         return False
 
@@ -153,6 +161,14 @@
     print('$ cd {}'.format(source))
     os.chdir(source)
 
+    if args.commit is not None:
+        if config['scm'] == 'git':
+            if not git_checkout(args.commit):
+                return False
+        elif config['scm'] == 'hg':
+            if not hg_update(args.commit):
+                return False
+
     if config['scm'] == 'git':
         if not git_status():
             return False
@@ -228,11 +244,11 @@
     return True
 
 
-def wrapper(config):
+def wrapper(config, args):
     print('# C&O job started: {}'.format(timestamp()))
     tmp = mkdtemp(prefix='candolint.')
 
-    if not execute(tmp, config):
+    if not execute(tmp, config, args):
         print('# C&O job failed')
 
     print('# C&O task: cleanup')
@@ -248,12 +264,14 @@
 
 def main():
     parser = ArgumentParser()
-    helptext = 'project configuration file (YAML)'
-    parser.add_argument('config', type=FileType('r'), help=helptext)
+    parser.add_argument(
+        'config', type=FileType('r'),
+        help='project configuration file (YAML)')
+    parser.add_argument('commit', nargs='?', help='commit to update to')
     args = parser.parse_args()
     config = yaml.safe_load(args.config)
     try:
-        wrapper(config)
+        wrapper(config, args)
     except:
         bad_exit()
         raise