Support for lazy loading of split bundles in pre-load scripts for Notebooks

[DonJayamanne]

Preloading scripts works as expected in output renderes. However if the preload script is a bundle that lazyloads other bundle scripts, then this doesn't work.

The reason this doesn't work is because WebPack will attempt to load the resource dynamically. However this can only be done if resources are using the vscode-resource scheme (which cannot be hardcoded).

Current approach in Python webiview notebook implementation

• We make use of __webpack_public_path__ variable, this is initialized to a global variable window.__PVSC_Public_Path
• In our webivew we initialize the above value as follows:
  window.__PVSC_Public_Path = "${webView.asWebviewUri(Uri.file(<Extension dir/xyz>)).toString()}/";

This option will not work with preload scripts for notebooks

• At the moment the only solution I can see is to dynamically generate a JS file with the above code in it
• Ensure the above JS file is preloaded first

Again, this might not work well

• Output renderers do not have access to asWebViewUri method, hence any attempt to generate this value based on active Notebook Editor is not guaranteed to work.
• We (extension authors) cannot assume this value is a constant across all webviews

@rebornix /cc

[connor4312]

@DonJayamanne what do you think of this approach? microsoft/vscode-notebook-renderer-starter@ebef3da In summary:

1. In the webpack config, record the relative path from the entrypoint filename to the output directory. (Not dealing with any extra fancy multi-entrypoint configs right now)
2. When the entrypoint loads, form and set the __webpack_public_path__ based on the url of the current script + the relative path we previously recorded

[DonJayamanne]

That works, that's pretty much what I'm doing today. As long as we have VSCodes blessing for such a solution I'm happy. Didn't want to make any assumptions about how the scripts are loaded and the like.
Closing as this issue.

Thanks again.

[connor4312]

I think this should be reliable.

cc @mattbierner as the webview master