/tree/<path> should redirect to /notebooks/<path> if <path> is a notebook file

[yuvipanda]

Problem

When redirecting users to a particular file (from nbgitpuller), it is important to not need prior knowledge on wether the target is a file or a directory. In lab and classic notebook, we can send people to /tree/<path>, it redirects to /notebooks/<path> if it's a notebook or /tree/<path> if it's just a directory, based on what ContentsManager says.

retrolab doesn't do that - if you go to /tree/<path> but <path> is a notebook you get an error.

Proposed Solution

retrolab/retrolab/app.py

Line 99 in 0f7c026

class RetroTreeHandler(RetroHandler):

currently handles redirects. We could either figure out a contentsmanager check here, or do that on the client side

[jtpio]

Thanks @yuvipanda.

Probably doing the redirect in that handle will be enough. RetroLab should then be able to handle URLs that look like /retro/notebooks/example.ipynb