[stdlib, 6.2] Handle String's 32-bit inline representation for Span #82587
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@swift-ci please test |
glessard
added
32 bit only
🍒 release cherry pick
DougGregor
approved these changes
Jun 27, 2025
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String's inline representation is currently non-contiguous on 32-bit platforms. Furthermore, that representation is baked in ABI for watchOS's 32-bit variant. This PR implements mitigations.
A. For 32-bit platforms without ABI stability, we reduce the size of the inline representation to 8 UTF-8 code units (from 10).
B. For 32-bit watchOS, we add an optional property var _span: Span<UTF8.CodeUnit>? that returns nil when the representation of the String is non-contiguous, that is when it is 9 or 10 UTF-8 code units.
All platforms will get this underscored property, so that code that supports 32-bit watchOS doesn't have to be specific to it.
Scope: Bug fix for 32-bit platforms
Radar/SR Issue: rdar://147500261
Main PR: #82442
Risk: Low
Testing: Covered by unit tests
Reviewer: @lorentey