Improvements to loading times of Python Extension

[DonJayamanne]

Following are some changes that can be made to improve the load times of the python extension:

Changes required

• Load 3rd party npm modules on demand #3018 Load 3rd party npm modules on demand (in code using require)
  Easy change, and should be done selectively, without having to sacrifice benefits of typechecking, etc.
• Create a liter to ensure npm modules are always loaded on demand (with ability to add exceptions, e.g. fs, child_process, etc).
• Perform all validation checks in the background #3019 Perform all validation checks (if interpreter is available, using default Mac Interpreter, etc) in the background (needs Spec).
• Activate parts of the extension in the background.
• Load language server in the background #3020 Load (and activate) language server in the background
  Document and notify LS and IC teams.
  • Provided intelli-code uses activate().ready things should work as expected
• WIP - Make the language server the default experience #2722 Download LS in the background
• Bundle extension into a single file #3021 Webpack bundling (with source maps)
  • Get this done first, so we have this in insiders build (that can be optionally turned off when necessary).

Long Term Changes:

• Create perf tests to measure and compare code load times of extension #3022 Create more perf tests to measure and compare load times of extension, in particular the following times:
  • codeLoadingTime
  • activateCallTime
  • activateResolvedTime
    We have tests today that do something similar, we need to ensure they are more granular. (compare against release and dev versions of extension - as done today).
• Change interpreters list into an Observable list #3023 Observable list of interpreters (currently we need any, subsribe, filter, and similar capabitlies of interpreters, but in a non-blocking way, thats exactly that Observable lists provide - RxJs).
  • Short term solution could be to add new code for perf improvements
  • E.g. add a predicate to IInterpreterService.getInterpreters, add methods IInterpreterService.hasAny, IInterpreterService.onChange()

@Microsoft/pvsc-team /cc