Upgrade to RN v0.61

[gnprice]

We won't meaningfully start on this until we complete the upgrade to RN v0.60, #3548. Filing to have an identifier to refer to. (We're now on v0.60.)

Released 2019-09. Release notes here:
https://facebook.github.io/react-native/blog/2019/09/18/version-0.61

Exciting improvements include:

• "Fast Refresh", which replaces both "live reload" and "hot reload", and is supposed to be more complete and reliable. That'd be a pretty great improvement to the dev experience!
• Flow v0.105. In particular this brings
  • (Flow v0.101) the implicit-inexact-object flowlint (which will help with some later steps of Convert all object types to exact, or explicitly-inexact #3452)
  • (Flow v0.100) more-precise React types
• React upgraded to 16.9. In particular this allows us to upgrade react-native-webview; see 44114f7.
• The old RN bug that makes TextInput slow after lots of typing is reportedly fixed: Upgrade to RN v0.61 #3781 (comment)
• A Metro bug which affects Node 12 on Windows is fixed, clearing the way to upgrade to Node 12 everywhere: Upgrade to Node v12 #3780
• We can probably upgrade react-native-unimodules: Upgrade to a react-native-unimodules without privacy-sensitive dead code #4091, and see chat on why v0.61 will help.
  • That may also let us drop a bit of Gradle code: #3548 (comment)

Possible incompatible changes, requiring work from us on upgrade, include:

• "Remove React .xcodeproj". IIUC, this basically requires us to have moved fully to CocoaPods, from the old way of configuring the iOS build; I believe we'll do this already as part of the work to upgrade to RN v0.60.
• That Flow upgrade, surely.
• (Surely there will be more. But maybe a lot less than the last couple of upgrades! Discussion at Upgrade to RN v0.61 #3781 (comment) .)

[rk-for-zulip]

(edit: mistaken, thankfully -- see #3781 (comment)) Debugger warnings in RN 0.60 indicate that the React componentWillReceiveProps lifecycle callback will be removed in RN 0.61. This callback is currently used in ComposeBox and AnimatedScaleComponent.

[gnprice]

One exciting change is that this old RN bug is reportedly fixed in v0.61!
facebook/react-native#20119

TextInput becomes slow after lots of typing

That's the mitigated version of the RN bug that got much worse back in v0.55 (vs. v0.54 and earlier), which our users experienced as #2589. I fixed that one upstream so that in v0.56 it was back to the level of v0.55 and earlier; but it's encouraging that the underlying bug now seems to be fixed too.

(Though there's still some uncertainty because, as discussed on that issue thread, nobody knows how it got fixed. 🤞 )

[gnprice]

I think it's likely that this upgrade will turn out to be a lot less work than the v0.60 upgrade (or the v0.59 upgrade before that.)

My information on this is circumstantial: it seems like for whatever reason a lot of people are (at least as of like a month ago) still on v0.59, and a lot are on v0.61 or v0.62, and very few are on v0.60. My data for that is from being subscribed to an RN issue thread where a few people a month report it's still broken for them, and I noticed sometime like a month ago that the reports in 2020-to-date or so followed that pattern. (Originally mentioned this the other day in chat.)

So, hopefully it turns out that way when we go to try it!

[gnprice]

Debugger warnings in RN 0.60 indicate that the React componentWillReceiveProps lifecycle callback will be removed in RN 0.61.

This isn't correct. Here's the warning:

YellowBox.js:71 Warning: componentWillReceiveProps is deprecated and will be removed in the next major version. Use static getDerivedStateFromProps instead.

Please update the following components: Connect(HomeTab), Connect(IconUnreadConversations), Connect(IconUnreadMentions), Connect(LoadingBanner), Connect(OfflineNotice), Connect(OwnAvatar), Connect(UnreadCards), SafeView

Learn more about this warning here:
https://fb.me/react-async-component-lifecycle-hooks

As the linked article explains, this is a React warning, and the "next major version" in question is React 17. There is not yet a React 17, so RN v0.61 doesn't use it. Nor does RN v0.62 (which is out already), or v0.63 (which has a release candidate out.)

[chrisbobbe]

EDIT: This has been resolved. Thanks, @gnprice!

I commented at #3635 (comment) about some new errors I'm seeing with Flow 105; it looks like that PR would make things more sensible in a way that probably eliminates those errors. 🙂