* import-url: support importing empty directories on object storage services
Empty directories are basically files with a trailing slash at the end of their names,
with empty contents on object service providers (such as azure, google storage). This
patch implements the `is_empty()` method for the `FSSpecWrapper` to determining whether
a path is empty (directory or a file) and also tweaks `.isdir()` in order to see empty
directories.
The base class is only used by azure and gcsfs for now, but if we go on the route of
migrating normal providers (like proper filesystems, not just object storages), we might
need to do these tweaks on a subclass (like `ObjectStorageFSSpecWrapper` etc), but I
don't think it is neccesary as of now.
The `is_empty` method is already there, and also used in the importing part to
warn users that they are importing something empty (https://github.com/iterative/dvc/blob/e385e59a098cd661ea1ea4257c9a5735c5c32bc6/dvc/output/base.py#L252-L254)
so this is not a new method. Just for the reference, as far as I can locate there
is no variant of this method in the fsspec.
* tests: revert custom mkdir for cloud storages
* tests: allign assingments
* add some comments
* s3: faster directory hashing
* Introduce Tree.info() API
* tests for s3
* Implement support for azure
* New .ls() API
* remove _iter_hashes from other trees
* assert recursive
* yield strings instead of file_infos
* Add GSTree.ls()
* Add DETAIL_FIELDS to the GSTree
* WebDAVTree.ls()
* proper webdav root directory initalization
* disable arguments-differ
Batuhan Taskaya
Saugat Pachhai
Ruslan Kuprieiev