Add development mode to lab extension build scripts

[jasongrout]

References

This is built on #8913, so that should be merged first.

Code changes

This adds a development option to lab extension building scripts. The default is to build in production mode.

Also renames static_path option to static_url.

User-facing changes

Backwards-incompatible changes

[jupyterlab-dev-mode]

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[blink1073]

Why not just merge this one since the rebase is done and build is in progress?

[blink1073]

Ah, I see you already rebased

[blink1073]

Thanks!

[blink1073]

I pushed fixes for examples and usage failures

[blink1073]

browser_check is failing with a dynamic extension:

[W 2020-08-27 14:36:28.825 ServerApp] '_build'
...
[W 2020-08-27 14:36:40.742 ServerApp] 404 GET /foo/lab?token=fa278731aea392936cec7c943c946ab5600f2e988fab7c37 (::1) 34.89ms referer=None

I think there is a problem looking up the _build metadata.

[blink1073]

The usage failure seems to have snuck in on #8913

[blink1073]

With 0e5be73 we get 404 GET /foo/lab/extensions/@jupyterlab/mock-extension/remoteEntry.js, which is expected until we make a release.

[jasongrout]

Two other things when I did this. I'd love your thoughts:

1. "static path" seems like a confusing name for an option, especially next to "core path". Really, it's a URL, most likely including the host, not a path on disk like the core path is.
2. (an implementation detail...) - I think we should pass values from build-labextension into the webpack config using the webpack cli env feature, rather than relying on environment variables.

[blink1073]

"static path" seems like a confusing name for an option, especially next to "core path". Really, it's a URL, most likely including the host, not a path on disk like the core path is.

Sure, static_url seems better, I'll update.

(an implementation detail...) - I think we should pass values from build-labextension into the webpack config using the webpack cli env feature, rather than relying on environment variables.

Makes sense to me.

[jasongrout]

Thanks for the cleanups!