[Abbondanzo]

Summary:

Android lays text out in lines a whole number of pixels tall, so CustomLineHeightSpan rounds a lineHeight up to the next whole pixel. That broke adjustsFontSizeToFit for text whose lines exactly fill its container:

• A lineHeight that isn't a whole number of pixels, such as 20dp at 420dpi (52.5px), is laid out as 53px, which doesn't fit the 52.5px its container leaves for it.
• A lineHeight that converts to a hair over a whole number of pixels, such as 44.000004px, is laid out a whole pixel taller than it asks for.

adjustsFontSizeToFit then shrinks the font. Shrinking it never makes a line with a fixed lineHeight shorter, so the text drops to the minimum font size, and text with numberOfLines greater than 1 collapses onto fewer lines.

• CustomLineHeightSpan no longer rounds a line height up past a whole number of pixels it only exceeds by floating point error, using the tolerance PIXEL_SIZE_TOLERANCE that the earlier changes added.
• adjustsFontSizeToFit compares the available height with the layout's height minus what rounding its line heights added, so text fits when its line heights, as given, fit. Text without a lineHeight is compared as before.

Adds unit tests and an RNTester example with nine one-line and nine two-line labels whose lines exactly fill their containers. Each label's line height is half a pixel taller than the last. Without this change, 10 of the 18 labels shrink at 420dpi and 8 at 320dpi.

Changelog:
[Android][Fixed] - Fix adjustsFontSizeToFit shrinking text whose lineHeight exactly fills its container

Differential Revision: D129646293

[meta-codesync]

@Abbondanzo has exported this pull request. If you are a Meta employee, you can view the originating Diff in D129646293.