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Don't grow smol Strings to 16 characters when bridging out if tagged pointer formation fails #84068

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Merged
merged 1 commit into from
Sep 4, 2025
+14 −17
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Don't grow smol Strings to 16 characters when bridging out if tagged pointer formation fails #84068

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31 changes: 14 additions & 17 deletions stdlib/public/core/StringBridge.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -623,31 +623,28 @@ extension String {

_connectOrphanedFoundationSubclassesIfNeeded()

// Smol ASCII a) may bridge to tagged pointers, b) can't contain a BOM
if _guts.isSmallASCII {
let maybeTagged = _guts.asSmall.withUTF8 { bufPtr in
return unsafe _createCFString(
if _guts.isSmall {
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This is mostly just rearranging the code to be a bit clearer. The substantive change is is switching from grow + recursing into bridgeToObjectiveCImpl -> __StringStorage.create, which should let us create the actual size we want rather than unnecessarily padded.

return unsafe _guts.asSmall.withUTF8 { bufPtr in
// Smol ASCII a) may bridge to tagged pointers, b) can't contain a BOM
if _guts.isSmallASCII, let result = unsafe _createCFString(
bufPtr.baseAddress._unsafelyUnwrappedUnchecked,
bufPtr.count,
kCFStringEncodingUTF8
)
}
if let tagged = maybeTagged { return tagged }
}

if _guts.isSmall {
// We can't form a tagged pointer String, so grow to a non-small String,
) {
return result
}
// We can't form a tagged pointer String, so make a non-small String,
// and bridge that instead. Also avoids CF deleting any BOM that may be
// present
var copy = self
// TODO: small capacity minimum is lifted, just need to make native
copy._guts.grow(_SmallString.capacity + 1)
_internalInvariant(!copy._guts.isSmall)
return copy._bridgeToObjectiveCImpl()
return unsafe __StringStorage.create(
initializingFrom: bufPtr,
codeUnitCapacity: bufPtr.count,
isASCII: _guts.isSmallASCII)
}
}
if _guts._object.isImmortal && !_guts._object.largeFastIsConstantCocoa {
if _guts.isASCII && _guts._object.isFastZeroTerminated {
let ptr = unsafe _guts._object.fastUTF8.baseAddress!
let ptr = unsafe _guts._object.fastUTF8.baseAddress._unsafelyUnwrappedUnchecked
let count = _guts.count
if let indirect = unsafe _stdlib_binary_createIndirectTaggedPointerNSString(
ptr: ptr, count: count
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