added item_count

[Rishab87]

Fixes #1491, This PR adds item_count

[krassowski]

This is looking good to me!

I think two things need to be added here:

• a test for item_count, probably somewhere here:
  

  jupyter_server/tests/services/contents/test_manager.py

  Line 550 in dd7daf9

  async def test_get(jp_contents_manager):

• a documentation entry in:
  

  jupyter_server/docs/source/developers/contents.rst

  Lines 34 to 38 in dd7daf9

  	Models may contain the following entries:
  	+--------------------+------------+-------------------------------+
  	| Key | Type | Info |
  	+====================+============+===============================+

  
  and
  

  jupyter_server/docs/source/developers/contents.rst

  Lines 107 to 112 in dd7daf9

  	- ``directory`` models
  	- The ``format`` field is always ``"json"``.
  	- The ``mimetype`` field is always ``None``.
  	- The ``content`` field contains a list of :ref:`content-free<contentfree>`
  	models representing the entities in the directory.
  	- The ``hash`` field is always ``None``.

I think this is fully backwards compatible but wanted to run it by @Zsailer to confirm.

[Rishab87]

@krassowski , I've changed tests and doc and ensured no tests are failing, ig its ready to be reviewed now

[krassowski]

does length of item_count should be equal to content's length? as content excludes some of the files

Very good point! I just checked in two file managers (Nautilus and Nemo) and both do show the "1 item" if a folder includes both a hidden file and a non-hidden file by default, but if user selects "show hidden files" then they show "2 items".

I wonder if there is a potential performance consideration here though..

[Rishab87]

For now I've added the filters to not count hidden files or any other file which are not visible on jupyter lab's file browser by default (which means item_count and len(contents) are equal),

But yeah I otherwise need to somehow know if a user has selected show hidden folders in settings if yes then count those files too,

not sure if it will cause any performance issues need to look into the code in more detail! Also noticed one more thing even after turning on show hidden folders in jupyter labs I was not able to see all files which were otherwise easily visible in files app, so I think it might not be necessary to add count of hidden folders or files especially if it may cause performance issues and can lead to inconsistent item counts and actual items visible though I can be completely wrong here