Enable React concurrent mode

[Kicu]

Glossary

React concurrent mode

Starting from react 18 we can run React in new concurrent way (which seems the way React team is moving). Concurrent mode enables a lot of new behaviours in react, most importantly renders can be interrupted by React, re-run or run more than once. This is supposed to make react more performant and webapps more responsive to user actions.
State of this in Expensify:

• on native apps after we migrated new arch and enabled Fabric - to my knowledge - we should already be running react concurrently
• on web we are running legacy mode and this PR enables concurrent mode

Further reading:

• https://vercel.com/blog/how-react-18-improves-application-performance and also
• https://react.dev/blog/2022/03/29/react-v18#what-is-concurrent-react

React StrictMode

<StrictMode> is a component that wraps the whole App in (or parts of App) and it runs extra checks and extra behaviors only in dev. So in essence it's a kind of devtool for developers, that should help catch tricky bugs that could be introduced when running concurrent mode. Mainly it renders every component twice (discarding the first render) and runs all effects twice.
This behaviour ☝️ of StrictMode is the source of most bugs that happen to us.

Note: StrictMode is not needed for concurrent react to work but it is much safer to use it.

https://react.dev/reference/react/StrictMode

Details

This PR enables running React 18+ in concurrent mode alongside using StrictMode.
I did not provide screenshots or videos because this affects the whole how React behaves, so in theory affects the whole app.

Done

• react concurrent mode turned on and whole App wrapped in <StrictMode>
• react-navigation fixed via patch; see details here: Enable React concurrent mode #42592 (comment)
• react-native-reanimated fixed via patch, however it should be released soon as the team is aware of StrictMode problems.
  The related upstream PRs are: Fix web exiting animation in StrictMode software-mansion/react-native-reanimated#6129 and Merge ViewDescriptors implementation software-mansion/react-native-reanimated#6123 and reanimated team expects correct version to be released in 2.13

List of known bugs & fixes

• react-navigation breaks on StrictMode - fixed via local patch - need to verify the legitness of said patch solved
• react-native-reanimated
  • animations not working - OS team will fix, we have local patch in the meantime
  • initial animation when entering Report sometimes flickers; this happens because of StrictMode so only in dev

Fixed Issues

$ #33531
PROPOSAL:

Tests

• Verify that web and native build and run
• test all the most important features of the app and verify nothing breaks

Offline tests

QA Steps

• verify that web and native app runs
• test all the most important features of the app and verify that nothing obvious breaks

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
  • MacOS: Desktop
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick)
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  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
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    • If any non-english text was added/modified, I verified the translation was requested/reviewed in #expensify-open-source and it was approved by an internal Expensify engineer. Link to Slack message:
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  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
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• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.js or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
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• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
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• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

MacOS: Desktop

[melvin-bot]

Hey! I see that you made changes to our Form component. Make sure to update the docs in FORMS.md accordingly. Cheers!

[Kicu]

This is unrelated but a source of warning in browser console - the ref was unused.
While working on updated React I wanted to get rid of as many console warnings as I can since it helps to find the actual React bugs

[roryabraham]

Sounds good, but may I suggest creating a separate PR to remove this ref?

[rayane-djouah]

Can you please revert this change as it's done in #44155

[Kicu]

react-navigation status

• react-navigation in version 6 (current stable) does not work well in StrictMode when using linkingConfig - which we do
• I created a simple RN app with reproduction of this behaviour and I have tested it using newer v7 version and it works, However react-navigation 7 is still in alpha: https://github.com/react-navigation/react-navigation/releases
• I asked @satya164 who is an author of react navigation and he said that it is unlikely for this fix to be backported to 6 and suggested we try version 7 - perhaps this is a good idea to try
• I have found the source of bug in v6 and compared the code to v7 and I was able to prepare a patch for expensify. I can't 100% guarantee at this point that the patch won't break something else, but it feels mostly safe - I only edited one file.

detailed description of patch

The source of problems for us is that inside useNavigationBuilder there is code that cleans state on component unmount here: https://github.com/react-navigation/react-navigation/blob/6.x/packages/core/src/useNavigationBuilder.tsx#L557-L561
Because of StrictMode navigation components will be rendered twice and their effects will run twice. This in turn means that when the navigation renders and runs for the second time, the state is already cleaned from the previous effect cleanup.

Then this check will trigger: https://github.com/react-navigation/react-navigation/blob/6.x/packages/core/src/useNavigationBuilder.tsx#L372 and there is no navigation happening at all.

The patch fixes this in a similar way to v7 branch.

CC @adamgrzybowski @WoLewicki for visibility

[adamgrzybowski]

As a follow up to @Kicu mentioning react-navigation 7. This version introduces two functionalities that we may be interested in:

• preload -> We could potentially use it for optimization and performance.
• popTo -> It may help us with simplifying the UP action implementation.

[melvin-bot]

@rayane-djouah Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

[Kicu]

@mountiny @roryabraham We're ready for liftoff 🚀

Web and native builds work, there are no crucial issues and app works. Now I think we need some heavy testing by QA's - I tested only the basic functionalities that I know about. If any bugs come up they could be rather tricky or non-obvious.

[WoLewicki]

Maybe we could open another PR with all the changes not strictly related to the StrictMode so they can be also tested and merged earlier if they work properly? This way, this PR would focus only on the StrictMode. And that other PR is merged before this one, you can just merge the newest main here. Wdyt @Kicu ?

[Kicu]

I'm not sure. Technically it will be easy to split this into only concurrent mode and only StrictMode and I could do it, but how much would this really improve the process?
In theory if QA people will test this on production build, then strictmode should not affect it in any way. Per docs:

All of these checks are development-only and do not impact the production build.

So maybe leaving this PR as is will just be simpler?

[jasperhuangg]

@Kicu @roryabraham I'm having trouble following how this code only runs on dev considering that the USE_REACT_STRICT-MODE flag is always true and isn't dependent on any environment variables. Can you explain?

I'm mainly asking because there's a crash happening here on staging that involves a component exceeding the max update depth.

[jasperhuangg]

Hmm taking a deeper look at the docs it seems there's logic within React's StrictMode implementation that prevents it from running effects twice on staging/production builds.

[Kicu]

@jasperhuangg indeed its the internal behavior of StrictMode, described in the React docs that makes it only work in dev.
https://react.dev/reference/react/StrictMode#enabling-strict-mode-for-entire-app
So I'm trusting react devs here. It should be safe to ship apps wrapped with strict mode to prod and expect strict mode will not do any of the checks.

The CONFIG flag is for the convenience of developers for quick testing locally why their code fails

[OSBotify]

🚀 Deployed to production by https://github.com/jasperhuangg in version: 9.0.3-7 🚀

platform	result
🤖 android 🤖	success ✅
🖥 desktop 🖥	success ✅
🍎 iOS 🍎	success ✅
🕸 web 🕸	success ✅

[OSBotify]

🚀 Deployed to production by https://github.com/Julesssss in version: 9.0.5-13 🚀

platform	result
🤖 android 🤖	success ✅
🖥 desktop 🖥	success ✅
🍎 iOS 🍎	success ✅
🕸 web 🕸	success ✅

[ikevin127]

👋 The introduction of StrictMode with this PR created the following dev issue:

• [Pay 7/30] [Dev] - [StrictMode] Attachments not loading and app crashes when click on loading preview from attachment  #44566

The issue was fixed by PR #45559, more details on the proposal here.

[ishpaul777]

👋 The introduction of concurrent mode caused Left hand menu and RHP to not open instantly when opening from link

The issue was fixed by PR #45778

[ahmedGaber93]

👋 The introduction of StrictMode cause this DEV issue #44235 and it fixed here #46483

Strict Mode will unmount then remount component on the first render

React 18 introduces a new development-only check to Strict Mode. This new check will automatically unmount and remount every component

see here

Bad
unmount will set value to true, then remount will not back it to false

const isUnmounted = useRef(false);
useEffect(() => {
  return () => {
      isUnmounted.current = true;
  };
}, []);  

Good
unmount will set value to true, then remount will back it to false

const isUnmounted = useRef(null);
useEffect(() => {
  isUnmounted.current = false; // remount will back value to false
  return () => {
      isUnmounted.current = true;
  };
}, []);