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Off-by-one error in precondition #5311

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2 changes: 1 addition & 1 deletion Sources/Foundation/DispatchData+DataProtocol.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,7 @@ extension DispatchData : DataProtocol {
}

public subscript(position: DispatchData.Index) -> UInt8 {
precondition(index <= position && position <= index + bytes.count)
precondition(index <= position && position < index + bytes.count)
return bytes[position - index]
}

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20 changes: 20 additions & 0 deletions Tests/Foundation/TestNSData.swift
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Expand Up @@ -4481,6 +4481,26 @@ extension TestNSData {
}
}

func test_dispatchDataRegionSubscriptBounds() {
if #available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *) {
let bytes: [UInt8] = [0xAA, 0xBB, 0xCC]
var data = DispatchData.empty
bytes.withUnsafeBytes { data.append($0) }

guard let region = data.regions.first else {
XCTFail("Expected a single region")
return
}

XCTAssertEqual(region.startIndex, 0)
XCTAssertEqual(region.endIndex, bytes.count)

for (offset, expected) in bytes.enumerated() {
XCTAssertEqual(region[region.startIndex + offset], expected)
}
}
}

func test_Data_increaseCount() {
guard #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *) else { return }
let initials: [Range<UInt8>] = [
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