Extension Compatiblity

[blink1073]

Fixes #2356.

Note: Populated the singletonPackages using the packages that export a token and @phosphor/widgets, which comprises the packages that are explicitly shared.

Sample output:

ValueError:
"@jupyterlab/python-tests@0.1.0" is not compatible with the current JupyterLab
Conflicting Dependencies:
Required	Actual	Package
^0.6.0  	^0.5.0	@jupyterlab/application

TODO:

• Update the release script to add the explicit deps from the listed extensions
• Use those deps along with singleton packages config to determine compat
• Use the compat information in list - show as invalid, offer verbose mode with full report
• Use the compat information when building - remove from templated package.json
• Add tests

[blink1073]

Going to wait until #2409 is merged to finish this, since there will be a lot of overlap.

[ellisonbg]

Trying some things out with this branch:

First I ran:

jupyter labextension uninstall @jupyterlab/help-extension

I then saw this:

(python34) $ jupyter labextension list
[ListLabExtensionsApp] JupyterLab v0.23.2
[ListLabExtensionsApp] Known labextensions:
[ListLabExtensionsApp] 
Uninstalled core extensiosn:
[ListLabExtensionsApp]     @jupyterlab/help-extension

But when I tried to install that extension again I got a Python exception that ended with:

ValueError: @jupyterlab/help-extension is not a valid JupyterLab extension

[ellisonbg]

I tried to link/unlink the mockextension and mockextension-incompat and it all worked as expected.

[ellisonbg]

extensiosn

[ellisonbg]

Tested latest changes locally and all is happy. Once the tests pass, let's merge!

[ellisonbg]

Come on Travis!