perf: Optimise render counts

[franky47]

The optimal number of renders should be:

• On mount: 1 (with the correct search params)
• On update, with shallow: true (the default): 2 (one for the internal state, and one when the URL has updated)
• On update, with shallow: false: 2 to 3, depending of whether we do optimistic URL updates and the time it takes for the server to respond and "update" the URL again

Progress

• useQueryStates now renders only once on mount (was 2 renders previously)
• useQueryStates now renders one less time (detecting query cache hits)
• Fixed a bug in the patch-history caching logic (for React Router & Remix), saving one extra render on shallow: false.

Baseline

app router - useQueryState - shallow: true, history: replace, startTransition: false should then render 2 times on updates: expected 5 to equal 3 
app router - useQueryState - shallow: true, history: push, startTransition: false should then render 2 times on updates: expected 5 to equal 3 
app router - useQueryStates - shallow: true, history: replace, startTransition: false should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: true, history: replace, startTransition: false should then render 2 times on updates: expected 6 to equal 3
app router - useQueryStates - shallow: true, history: push, startTransition: false should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: true, history: push, startTransition: false should then render 2 times on updates: expected 6 to equal 3
app router - useQueryStates - shallow: false, history: replace, startTransition: false should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: replace, startTransition: false should then render 3 times on updates: expected 5 to equal 4
app router - useQueryStates - shallow: false, history: replace, startTransition: false, delay: 50ms should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: replace, startTransition: false, delay: 50ms should then render 3 times on updates: expected 6 to equal 4
app router - useQueryStates - shallow: false, history: replace, startTransition: true should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: replace, startTransition: true should then render 3 times on updates: expected 5 to equal 4
app router - useQueryStates - shallow: false, history: replace, startTransition: true, delay: 50ms should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: replace, startTransition: true, delay: 50ms should then render 3 times on updates: expected 6 to equal 4
app router - useQueryStates - shallow: false, history: push, startTransition: false should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: push, startTransition: false should then render 3 times on updates: expected 5 to equal 4
app router - useQueryStates - shallow: false, history: push, startTransition: false, delay: 50ms should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: push, startTransition: false, delay: 50ms should then render 3 times on updates: expected 5 to equal 4
app router - useQueryStates - shallow: false, history: push, startTransition: true should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: push, startTransition: true should then render 3 times on updates: expected 5 to equal 4
app router - useQueryStates - shallow: false, history: push, startTransition: true, delay: 50ms should render once on mount: expected 2 to equal 1
app router - useQueryStates - shallow: false, history: push, startTransition: true, delay: 50ms should then render 3 times on updates: expected 6 to equal 4

Tasks

• Investigate why wrapping URL updates with startTransition causes 4 renders in the pages router -> maybe the isLoading flag?
• Add test to React Router based frameworks (there were differences whether the loader function was defined or not, that will require two different pages)
• Add test to React SPA
• Investigate flakiness on test run (looks to be caused by CPU load, getting a lot more flakes on older machines when running 5 Cypress instances in parallel)

Click to expand

  Render count - app router - useQueryState - shallow: false, history: push, startTransition: true
render
    ✓ should render once on mount (84ms)
render
    (Attempt 1 of 2) should then render 3 times on updates
      cy:command ✔  visit	/app/render-count/useQueryState/false/push/true?delay=0
      cy:command ✔  contains	#hydration-marker, hydrated
      cy:command ✔  assert	expected **<div#hydration-marker>** to be **hidden**
      cy:command ✔  stub-1	log("render")
      cy:command ✔  get	button
      cy:command ✔  click	
      cy:command ✔  stub-1	log("render")
      cy:command ✔  stub-1	log("render")
      cy:command ✔  new url	http://localhost:3001/base/app/render-count/useQueryState/false/push/true?delay=0&test=pass
        cy:fetch ➟  GET http://localhost:3001/base/app/render-count/useQueryState/false/push/true?delay=0&test=pass&_rsc=vqr5f
                    Status: 200
      cy:command ✔  stub-1	log("render")
      cy:command ✔  stub-1	log("render")
      cy:command ✔  get	@consoleLog
      cy:command ✘  assert	expected **5** to equal **4**
                    Actual: 	5
                    Expected: 	4


render
    1) should then render 3 times on updates
      cy:command ✔  visit	/app/render-count/useQueryState/false/push/true?delay=0
      cy:command ✔  contains	#hydration-marker, hydrated
      cy:command ✔  assert	expected **<div#hydration-marker>** to be **hidden**
      cy:command ✔  stub-1	log("render")
      cy:command ✔  get	button
      cy:command ✔  click	
      cy:command ✔  stub-1	log("render")
      cy:command ✔  stub-1	log("render")
      cy:command ✔  new url	http://localhost:3001/base/app/render-count/useQueryState/false/push/true?delay=0&test=pass
        cy:fetch ➟  GET http://localhost:3001/base/app/render-count/useQueryState/false/push/true?delay=0&test=pass&_rsc=vqr5f
                    Status: 200
      cy:command ✔  get	@consoleLog
      cy:command ✘  assert	expected **3** to equal **4**
                    Actual: 	3
                    Expected: 	4
      cy:command ✔  stub-1	log("render")

Notes

• Render counts are wildly different on React Router versions (6 vs 7 vs Remix), since everything else is the same, it feels like we're testing the frameworks.. At least it gives us a baseline to go down from.
• Defining startTransition almost always causes one extra render. That could be the isLoading flag toggling. It does not cause one in RRv6 though.

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