Refactor trackViews() to reliably remove views

Created by: lguychard

Fixes #4064

Refactors trackViews() to stop relying on a ViewResolver's selector to detect removed views. We now inspect removedNodes to see if any of the removed nodes is a known view, or contains one or more known views.

With this refactor, the viewStates logic is now encapsulated within trackViews(), which simply emits every added views as a ViewWithSubscriptions, and takes care of calling view.subscriptions.unsubscribe() when the view is removed from the page. This prevents the consumer from having to reimplement the viewStates pattern.

Test plan: The view addition/removal logic is well tested by existing unit tests, but performance should be benchmarked as view removal is now more expensive.

TODO:

• Fix remaining failing test handleContentViews() › detects addition, mutation, and removal of content views
• Consider consolidating code_views.test.ts with views.test.ts

Created by: lguychard

I've looked at some profiles and interestingly, this performs consistently better than the status quo.

Test protocol:

• Start on !2344 (merged), make sure all 75 code views are added
• Click to navigate to the "Conversation" tab
• Profile from mouseup to the end of the following animation frame

Baseline: no Sourcegraph extension activated:

Sourcegraph dev extension built from master:

Sourcegraph dev extension built from this branch:

Another takeaway is that GitHub performance for this user action (switching between tabs on a large PR) is bad to start with, and we make it at least 2x worse

Created by: codecov[bot]

Codecov Report

Merging #4371 into master will decrease coverage by 0.02%. The diff coverage is 85.58%.

Impacted Files	Coverage Δ
browser/src/libs/code_intelligence/text_fields.tsx	88.09% <100%> (-1.27%)
...r/src/libs/code_intelligence/code_intelligence.tsx	70.31% <80%> (-0.06%)
...rowser/src/libs/code_intelligence/content_views.ts	94.11% <91.3%> (-5.89%)
browser/src/libs/code_intelligence/views.ts	96.42% <95%> (-3.58%)
cmd/gitserver/server/serverutil.go	49.15% <0%> (-2.65%)
cmd/repo-updater/repos/syncer.go	78.53% <0%> (-2.1%)
pkg/diskcache/cache.go	44.09% <0%> (-1.23%)