1 files changed, 29 insertions, 0 deletions
diff --git a/fastimport/helpers.py b/fastimport/helpers.py
index 05cce6f..8e9a383 100644
--- a/fastimport/helpers.py
+++ b/fastimport/helpers.py
@@ -92,4 +92,33 @@ def binary_stream(stream):
     return stream
 
 
+def common_directory(paths):
+    """Find the deepest common directory of a list of paths.
+
+    :return: if no paths are provided, None is returned;
+      if there is no common directory, '' is returned;
+      otherwise the common directory with a trailing / is returned.
+    """
+    from bzrlib import osutils
+    def get_dir_with_slash(path):
+        if path == '' or path.endswith('/'):
+            return path
+        else:
+            dirname, basename = osutils.split(path)
+            if dirname == '':
+                return dirname
+            else:
+                return dirname + '/'
+
+    if not paths:
+        return None
+    elif len(paths) == 1:
+        return get_dir_with_slash(paths[0])
+    else:
+        common = common_path(paths[0], paths[1])
+        for path in paths[2:]:
+            common = common_path(common, path)
+        return get_dir_with_slash(common)
+
+