Subdir support

repo2docker/app.py

@@ -62,6 +62,16 @@ class Repo2Docker(Application):
         """
     )
 
+    subdir = Unicode(
+        '',
+        config=True,
+        help="""
+        Subdirectory of the git repository to examine.
+
+        Defaults to ''.
+        """
+    )
+
     buildpacks = List(
         [
             LegacyBinderDockerBuildPack,
@@ -345,6 +355,12 @@ class Repo2Docker(Application):
             help=self.traits()['appendix'].help,
         )
 
+        argparser.add_argument(
+            '--subdir',
+            type=str,
+            help=self.traits()['subdir'].help,
+        )
+
         argparser.add_argument(
             '--version',
             dest='version',
@@ -482,6 +498,9 @@ class Repo2Docker(Application):
                   'the container')
             sys.exit(1)
 
+        if args.subdir:
+            self.subdir = args.subdir
+
         self.environment = args.environment
 
     def push_image(self):
@@ -644,7 +663,7 @@ class Repo2Docker(Application):
             if self.repo_type == 'remote':
                 self.fetch(self.repo, self.ref, checkout_path)
 
-            os.chdir(checkout_path)
+            os.chdir(os.path.join(checkout_path, self.subdir).rstrip('/'))
 
             for BP in self.buildpacks:
                 bp = BP()