Skip to content

Extension API context evaluation/parsing significantly slows down switching tabs on GitHub

Created by: felixfbecker

To reproduce:

  • Open a PR on GitHub, go to the files tab and make sure the code views/extensions get initialised (get a hover).
  • Now switch the tab back to "discussion", or to "issues", something that removes the code view again.
  • This switching is significantly delayed compared to without the browser extension running, indicating the JavaScript main thread is blocked on something CPU intensive.
  • Switching back and forth now exhibits the same behaviour

Profiling reveals that most time is spent parsing context expressions:

image

image

Potential solutions:

  • Can we optimise the evaluation process? E.g. reduce the amount of things that need to be recomputed, don't recompile expressions on new code views but just reevaluate them
  • Can we run this CPU-intensive work in the background script / extension host instead?
  • Can we do away with context expression parsing completely?

I found one TODO in this file, could this help? https://sourcegraph.com/github.com/sourcegraph/sourcegraph@d5467869681e187eb19199b2848aede9598b61f1/-/blob/shared/src/api/client/services/contribution.ts#L127:1

cc @sqs

Profile: Browser Extension ext API slowdown profile.json.zip