Use extensionapp open_browser trait for serverapp config

[echarles]

This is a fix for #215

It uses the ExtensionApp open_browser trait for ServerApp config.

[echarles]

@Zsailer Do we have a replicable CI failure on ubuntu py3.7 (tests/test_terminal.py)?

[davidbrochart]

I'm having the same failure over in #218.

[davidbrochart]

I cannot reproduce the failure locally on an Ubuntu / python3.7.

[Zsailer]

Yeah, that test is flaky on all platforms. I've tried increasing the timeout in the await call, but still no luck.

[Zsailer]

LGTM! Thanks, @echarles

[maartenbreddels]

This PR breaks voila (with this branch voila-dashboards/voila#592) , cls.open_browser is the trait itself, not the value of the trait. It will lead to this exception:

traitlets.traitlets.TraitError: The 'open_browser' trait of a ServerApp instance must be a boolean, but a value of <traitlets.traitlets.Bool object at 0x10ed7f940> <class 'traitlets.traitlets.Bool'> was specified.

[echarles]

Tried to get the value from the Bool trait without luck. Docs and google didn't help me. Any pointer?

[davidbrochart]

I don't think it's possible. You can only observe traits and get the changes with old and new keys IIRC.

[blink1073]

It is definitely possible. I'm afk but can give an example later

[maartenbreddels]

You need the instance of cls to access the value, not the class. We can take the default value, but I guess we want the configured value right?

[echarles]

Tried different methods (from class and instance), but I can only access the default value, not the configured value. We indeed need the configured value.

[Zsailer]

Wow—I completely missed this in the review. Sorry y'all.

I think this is the wrong way to do this—but I think this will be solved by idea proposed in #207—add a step for extensions to configure the server before the server is initialized.

[echarles]

My bad... Before opening that PR I had done some sanity check launching a server and it was not breaking. The command I have used is jupyter server --ServerApp.jpserver_extensions="{'simple_ext1': True}" --SimpleExt1.open_browser=False which does not break and does not open the browser... but if you set --SimpleExt1.open_browser to True the browser is also not launched.

If you launch via entrypoint jupyter simple-ext1, you break...

I have been confused a few time with the difference in behavior when you launch via jupyter server or via the entrypoint...

Also not sure if the unit tests cover the entrypoints - Prolly was green because the test enable the extension via ServerApp.jpserver_extensions

[echarles]

Agree as this is a global server config, we should have #207 to handle that.

[echarles]

I have been confused a few time with the difference in behavior when you launch via jupyter server or via the entrypoint...

... so I have just opened #230

[echarles]

@Zsailer @maartenbreddels Any hint to get the boolean from the Bool trait? If we can not get this working, I will open a new PR to rollback this breaking change.