[SR-6361] Data.withUnsafeMutableBytes() crash

[swift-ci]

Previous ID	SR-6361
Radar	None
Original Reporter	sashabelonogov (JIRA User)
Type	Bug
Status	Closed
Resolution	Done

Environment

macOS 10.12.6, Xcode 9.0, Swift 4.0

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Bug
Assignee	sashabelonogov (JIRA)
Priority	Medium

md5: 30798dd20aad53ebbf352c04dbf2174d

Issue Description:

This example:

var data = Data(bytes: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9])[4..<6]
        data.withUnsafeMutableBytes { (ptr: UnsafeMutablePointer<UInt8>) in
            ptr.advanced(by: 1).pointee = 0xFF
        }

crashes with:

fatal error: UnsafeMutableRawBufferPointer with negative count

[swift-ci]

Comment by Alexander Belonogov (JIRA)

Here is a potential fix to this issue: #1314