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use-subscription tearing fix #16623

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merged 3 commits into from
Sep 5, 2019
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bvaughn
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@bvaughn bvaughn commented Aug 30, 2019

Adds a test (previously failing) and a fix for a potential tearing case reported in #16396.

Resolves #16396

jest.runAllTimers();

// Partial update "C" -> "D"
// Interrupt with a second mutation "D" -> "E" but this should not cause tearing.
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This second interrupting mutation is required to trigger the previous failure. (Described in more detail in this issue comment.) I don't yet understand why this is but will be digging in more.

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It looks like React eagerly computes the state initially, for the first update. It doesn't do this or subsequent updates though because expirationTime !== NoWork.

I'm not sure if this is expected, given that my test flushes all pending work.

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@acdlite and I chatted about this offline and I have a better understanding of it now. I've updated the inline test comments. Going to hand this PR to him since he has full context now too.

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sizebot commented Aug 30, 2019

Details of bundled changes.

Comparing: f962feb...5ba5309

use-subscription

File Filesize Diff Gzip Diff Prev Size Current Size Prev Gzip Current Gzip ENV
use-subscription.development.js +5.0% +4.4% 6.67 KB 7 KB 2.61 KB 2.72 KB NODE_DEV
use-subscription.production.min.js -0.3% -0.2% 1.72 KB 1.71 KB 922 B 920 B NODE_PROD

Generated by 🚫 dangerJS against 5ba5309

@bvaughn bvaughn requested a review from acdlite August 30, 2019 21:59
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bvaughn commented Sep 4, 2019

Ping @acdlite :)

@bvaughn bvaughn merged commit d96f478 into facebook:master Sep 5, 2019
@bvaughn bvaughn deleted the use-subscription-tearing branch September 5, 2019 18:12
This was referenced Oct 5, 2019
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use-subscription causes UI tearing in some random cases
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