fix(ios): Fix rounding error occurring randomly in iOS text line height calculation

[soutua]

Summary:

Fixes issue #53450

There are some discussion and explanation about the issue here: #53450 (comment)

In short, there seems to be a rounding error occurring with the new architecture's implementation when the text paragraph line heights are calculated on iOS, that happens randomly and depends on what text content the view has, and on the device screen.

The fix is basically the same that had been implemented in the React Native's old architecture 8 years ago, but hasn't been brought into the new architecture implementation. The fix adds a fraction to the text line dimensions to mitigate the rounding error.

Changelog:

[IOS] [FIXED] - Fix rounding error occurring randomly in iOS text line height calculation

Test Plan:

Note that the reproduction of the issue is also dependant on the used device/simulator, this was tested using the iPhone 17 simulator.

• Go to Text Layout Example in the RNTester app
• Scroll down the text until you see this text paragraph:

Without the fix:

With the fix:

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[cipolleschi]

@soutua thanks for the fix!

[meta-codesync]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this in D85438723.

[emaestre]

Hey guys! Thank you so much for the fix 🚀 is there any timeline to get this released? I think that a lot of apps are having this trouble.

Thanks!

[cipolleschi]

Hey @soutua
Can I ask you to:

1. rebase
2. add an example screen in RNTester
3. show the before and after in the TestCase. So basically we want to see the problem before the fix and the problem fixed after the fix.

@emaestre the steps are:

1. The PR needs to be merged
2. if it is merged before friday of the next week, it will be released in 0.83
3. if you guys needs this fix in a previous version of react native, we need a cherry pick request
4. After the commit is picked, it will be included in the next patch release of the version.

[soutua]

Hey @soutua Can I ask you to:

1. rebase
2. add an example screen in RNTester
3. show the before and after in the TestCase. So basically we want to see the problem before the fix and the problem fixed after the fix.

I've now rebased and added a new text layout example screen in the RNTester app, I've also updated the test plan in the issue description to showcase the before/after difference.