s3: add support for top level empty directories

dvc/remote/s3.py

@@ -212,6 +212,15 @@ class RemoteS3(RemoteBASE):
         fname = next(self._list_paths(path_info, max_items=1), "")
         return path_info.path == fname or fname.startswith(dir_path.path)
 
+    def makedirs(self, path_info):
+        # We need to support creating empty directories, on S3, that means
+        # creating an object with an empty body and a trailing slash `/`.
+        #
+        # We are not creating directory objects for every parent prefix,
+        # it doesn't make sense.
+        dir_path = path_info / ""
+        self.s3.put_object(Bucket=path_info.bucket, Key=dir_path.path, Body="")
+
     def isdir(self, path_info):
         # S3 doesn't have a concept for directories.
         #
@@ -271,4 +280,7 @@ class RemoteS3(RemoteBASE):
 
     def walk_files(self, path_info, max_items=None):
         for fname in self._list_paths(path_info, max_items):
+            if fname.endswith("/"):
+                continue
+
             yield path_info.replace(path=fname)

tests/unit/remote/test_s3.py

@@ -79,9 +79,11 @@ def test_walk_files(remote):
         remote.path_info / "data/subdir/1",
         remote.path_info / "data/subdir/2",
         remote.path_info / "data/subdir/3",
+        remote.path_info / "empty_file",
+        remote.path_info / "foo",
     ]
 
-    assert list(remote.walk_files(remote.path_info / "data")) == files
+    assert list(remote.walk_files(remote.path_info)) == files
 
 
 def test_copy_preserve_etag_across_buckets(remote):
@@ -99,3 +101,11 @@ def test_copy_preserve_etag_across_buckets(remote):
     to_etag = RemoteS3.get_etag(s3, "another", "foo")
 
     assert from_etag == to_etag
+
+
+def makedirs(remote):
+    empty_dir = remote.path_info / "empty_dir"
+    remote.remove(empty_dir)
+    assert not remote.exists(empty_dir)
+    remote.makedirs(empty_dir)
+    assert remote.exists(empty_dir)