Generic view from command execution in a web browser tab.

[fcollonval]

Problem

In #6315, support for custom document factory was added to ease cross support for Lab and Notebook 7+. But extensions may open new views in the main area of JupyterLab that are not related to a factory (I'm thinking to diff / merge views from nbdime or jupyterlab-git for example). This issue goal is to initiate a discussion to design a way in Notebook to open a widget in a new browser tab not related to a document factory.

Proposed Solution

Let's take an example:

1. The user open the git panel file status in a tab on the /tree page
2. They click on a button to see the difference to be committed on file modifiedA.txt
3. It displays the diff view in a new web browser tab.

Technically, a solution would be to have the command opening the document will in JupyterLab instantiate a widget and add it to the main area. But in notebook, that command will be wrapped in a dispatcher that will open a new browser tab with the command and the serialized-JSON args to be executed to get the content of the page.

One open question is how to pass the command and associated args:

• Option 1: through the page config object
  This will be safer and more controlled.
• Option 2: through query arguments
  This could be bookmarked or called from URL directly - but it may increase the attack surface by allowing any commands to be executed from a URL.
  The args size may exceed query arguments limitation.

Additional context