[hryhoriiK97]

Summary:

-[RCTTextLayoutManager processTruncatedAttributedText:textContainer:layoutManager:] (ReactCommon/react/renderer/textlayoutmanager/platform/ios/react/renderer/textlayoutmanager/RCTTextLayoutManager.mm) runs on every measure and every draw of a <Text> with numberOfLines. When the last line is truncated, it gives the ellipsis the colors of the character before it.

Current behavior. For the truncated range it removes and re-adds NSForegroundColorAttributeName and NSBackgroundColorAttributeName unconditionally. Editing the text storage discards the layout TextKit just computed, so inside drawAttributedString: the paragraph is laid out a second time before its glyphs are drawn. In the common case the range already carries those colors (any single-color <Text numberOfLines={...}>), so the edit changes nothing but still costs a full layout.

With this change. Before editing, it checks with one longestEffectiveRange lookup whether the whole truncated range already carries the attribute of the preceding character, and leaves the storage untouched when it does. A truncated range with other colors is recolored as before.

Changelog:

[IOS] [CHANGED] - Truncated Text no longer lays out again on every draw when its ellipsis already has the right color

Test Plan:

• node scripts/clang-format.js --check on the changed file passes.
• RNTester built with xcodebuild in Release and run on a physical iPhone 15 Pro (iOS 26.6.1).
• Same output.
  • Screenshots of a list of 1000 single-line truncated labels in bordered cards are byte-identical in the list area with and without the change.
  • Four truncated multi-color labels (a single-color tail after a differently colored start, alternating foreground colors, alternating background colors, and a color change shortly before the cut) are byte-identical with and without the change, and each ellipsis takes the color of the character before it.
  • In the RNTester Text examples (25 screens of scrolling), screens captured at the same scroll position are byte-identical. Screens that landed a few points apart differ only in the blur under the translucent tab bar and, by 1 level, at the edge of one translucent rounded View; no text pixel differs.
• Measurement. The two arms are the same binary with the change switched by a launch argument, in the order before, after, after, before. Taps and swipes were driven by Argent on the physical iPhone. Timed: the total time in -[RCTParagraphTextView drawRect:], and the time from the end of a mount to the CoreAnimation commit, which contains the drawing. iPhone 15 Pro, Release:

RNTester FlatList "Basic" example, 16 flings down and 16 up per launch	before	this PR	change
text drawing per draw (about 570 draws per launch)	983 µs	510 µs	−48%
text drawing per launch	561 ms	293 ms	−48%

RNTester Playground, 1000 single-line truncated labels, 10 mounts per arm	before	this PR	change
text drawing per mount	420.1 ms	115.8 ms	−72%
end of mount to CoreAnimation commit	480.5 ms	173.5 ms	−64%

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