[swift-dev] Foundation Data Behavior Different (read: crashes) in Swift 3.1 and Swift 3.2

[Ryan Lovelett]

Understood. Luckily we had a pretty decent test suite that caught this.
Thanks for working through that with me Philippe.
On Thu, Aug 24, 2017, at 03:35 PM, Philippe Hausler wrote:
> This is expected behaviors of collections and their slices. The
> previous result was a bug.> 
> I agree that collections in general and their slices need more
> documentation.> 
> Sent from my iPhone
> 
> On Aug 24, 2017, at 11:28 AM, Ryan Lovelett <swift-
> dev at ryan.lovelett.me> wrote:>> I think your onto it Philippe but then why is it behaving that way?
>> 
>> I updated my earlier script (attached) and added 2 things.
>> 
>>   1. print("Start: \(data.startIndex), End: \(data.endIndex), Count:
>>      \(data.count)") after the data.removeFirst(4).>>   2. The startIndex offset you suggested.
>> 
>> It no longer crashes. Hooray!
>> 
>> Swift 3.1:
>> 
>> Start: 0, End: 2, Count: 2
>> Base64: QWE=, String: Aa
>> 
>> Swift 3.2:
>> 
>> Start: 4, End: 6, Count: 2
>> Base64: QWE=, String: Aa
>> 
>> Oh wait. Woah. That's a really subtle change that has some very real
>> consequences.>> 
>> Is this expected and/or documented? Because I certainly would not
>> have expected that drastic of a change. I'll obviously need to go
>> read a lot more of the changes between Swift 3.1 and Swift 3.2 if
>> these sorts of changes are in scope.>> 
>> 
>> On Thu, Aug 24, 2017, at 02:10 PM, Philippe Hausler wrote:
>>> I see the issue.. the latest version traps (appropriately so).
>>> 
>>> let str = String(bytes: data[..<2], encoding: .utf8)!
>>> 
>>> The sub-range of the slice you have is incorrectly indexed. Try this
>>> out (I am presuming this is what you mean):>>> 
>>> let str = String(bytes: data[data.startIndex..<(data.startIndex +
>>> 2)], encoding: .utf8)!>>> 
>>>> On Aug 24, 2017, at 11:07 AM, Philippe Hausler <phausler at apple.com>
>>>> wrote:>>>> 
>>>> Is there a radar or bugs.swift.org ticket filed on this?
>>>> 
>>>> I presume because of the import this is a Darwin thing and not a
>>>> linux thing.>>>> 
>>>>> On Aug 24, 2017, at 11:05 AM, Michael Gottesman via swift-dev <swift-
>>>>> dev at swift.org> wrote:>>>>> 
>>>>> 
>>>>>> On Aug 24, 2017, at 10:47 AM, Ryan Lovelett via swift-dev <swift-
>>>>>> dev at swift.org> wrote:>>>>>> 
>>>>>> I've found what I believe is a bug. Though I'm unclear if the bug
>>>>>> is in>>>>>> Swift 3.1 or Swift 3.2/4.0. All I can say for sure is the
>>>>>> behavior is>>>>>> quite drastically different between the two.
>>>>>> 
>>>>>> For the code below (and attached):
>>>>>> 
>>>>>>  import Cocoa
>>>>>> 
>>>>>>  var data = Data(bytes: [0x50, 0x4B, 0x01, 0x02, 0x41, 0x61])
>>>>>>  data.removeFirst(4)
>>>>>>  let base64 = data.base64EncodedString()
>>>>>>  let str = String(bytes: data[0..<2], encoding: .utf8)!
>>>>>>  print("Base64: \(base64), String: \(str)")
>>>>>> 
>>>>>> If I compile and run that with the Swift included in Xcode 8.3.3
>>>>>> (e.g.,>>>>>> swift ./data-bug.swift) it outputs: Base64: QWE=, String: Aa.
>>>>>> Which is>>>>>> what I expect.
>>>>>> 
>>>>>> With the Swift that is included with Xcode 9.0 beta 6 (9M214v)
>>>>>> (e.g.,>>>>>> swift -swift-version 3 ./data-bug.swift). It performs an illegal>>>>>> hardware instruction and crashes. It also does this if I use use
>>>>>> the>>>>>> version 4 of the compiler.
>>>>>> 
>>>>>> Is this a bug? If so where is the bug? Was this always meant to
>>>>>> not work>>>>>> and Swift 3.1 just happened to work or is there now an issue in
>>>>>> the>>>>>> Swift 3.2 implementation?
>>>>> 
>>>>> I have not engaged my brain with the particulars of the rest of
>>>>> the email, but high level question: does this happen without
>>>>> optimization? Or does it happen only with optimization?>>>>> 
>>>>> Michael
>>>>> 
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>>>>> 
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>> 
>> <data-bug.swift>

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