[swift-users] Runtime crash caused by (NS)CharacterSet.hasMember?

[Jens Persson]

Filed 32748795

On Tue, Jun 13, 2017 at 10:55 PM, David Hart <david at hartbit.com> wrote:

> Worth a radar to improve docs.
>
> On 13 Jun 2017, at 22:12, Jens Persson via swift-users <
> swift-users at swift.org> wrote:
>
> Thanks!
>
> The documentation that Xcode displays (for CharacterSet's
> hasMember(inPlane plane:)) is as follows:
>
> Declaration:
> func hasMember(inPlane plane: UInt8) -> Bool
>
> Description:
> Returns true if the `CharacterSet` has a member in the specified plane.
> This method makes it easier to find the plane containing the members of
> the current character set.
> The Basic Multilingual Plane (BMP) is plane 0.
>
> Parameters:
> plane - No description
>
> Which is about the same as here:
> https://developer.apple.com/documentation/foundation/
> characterset/1779728-hasmember
> and here:
> https://developer.apple.com/documentation/foundation/
> nscharacterset/1412406-hasmemberinplane
>
> No where does it mention anything about undefined behavior for some values
> of plane.
>
> In order to find that crucial info, I'd have to do what you did, write it
> in Objective C and dig through the stack trace, or just guess that it calls
> CFCharacterSetHasMemberInPlane and that its documentation contains very
> valuable pieces of information that for some reason got lost on the way to
> NSCharacterSet's method hasMemberInPlane ...
>
> Kind of makes one wonder what other undocumented undefined behavior might
> hide in Foundation and other places.
>
> /Jens
>
>
>
>
> On Tue, Jun 13, 2017 at 7:14 PM, Doug Hill via swift-users <
> swift-users at swift.org> wrote:
>
>> I tried your calls to NSFont in Objective-C, and it also crashes. Looking
>> at the stack trace, I see that it crashes in CFCharacterSetHasMemberInPlane.
>> I see documentation for thePlane parameter of this function says:
>>
>> The valid value range is from 0 to 16.  If the value is outside of the
>> valid plane number range, the behavior is undefined.
>>
>> I guess randomly crashing counts as undefined behavior.
>> While it would be great if this function was more robust, Apple is
>> definitely saying Don’t Do That.
>>
>> Doug Hill
>> https://github.com/djfitz/SFFontFeatures
>>
>>
>> On Jun 13, 2017, at 9:42 AM, Jens Persson via swift-users <
>> swift-users at swift.org> wrote:
>>
>> PS
>> There are only 17 planes in the (current?) Unicode standard, but I'm
>> assuming that the CharacterSet.hasMember(inPlane:) shouldn't (randomly?)
>> crash for UInt8 values other than 0 ... 16?
>> It also seems strange that it reproducibly crashes or not depending on
>> which specific font I use.
>>
>>
>> On Tue, Jun 13, 2017 at 4:00 PM, Jens Persson <jens at bitcycle.com> wrote:
>>
>>> The below program demonstrates a possible bug that I encountered.
>>> Can anyone else reproduce my results (as explained in the comments)?
>>> If so, is it a Swift or Cocoa bug (I haven't tried it in Objective C)?
>>>
>>> import AppKit
>>>
>>> extension NSFont {
>>>     var planesWithMembers: [UInt8] {
>>>         return (UInt8(0) ... UInt8(255)).filter {
>>>             // The follwing line will crash (EXC_BAD_ACCESS) for some
>>> fonts:
>>>             coveredCharacterSet.hasMember(inPlane: $0)
>>>             // I have tested it with Xcode 8.3.3 and Xcode 9 beta 1, both
>>>             // Swift 3 and 4, and they all reproduce the crash.
>>>             // macOS 10.12.5
>>>         }
>>>     }
>>> }
>>>
>>> // Examples that will not cause the crash:
>>> // let fontName = "AlBayan"
>>> // let fontName = "AppleBraille"
>>> // let fontName = "Chalkboard"
>>> // let fontName = "Helvetica"
>>> // let fontName = "Zapfino"
>>>
>>> // Examples that will cause the crash:
>>> // let fontName = "AppleColorEmoji"
>>> // let fontName = "AppleSymbols"
>>> let fontName = "Baskerville"
>>> // let fontName = "Geneva"
>>> // let fontName = "SnellRoundhand"
>>>
>>> let font = NSFont(name: fontName, size: 12)!
>>> let result = font.planesWithMembers
>>> print("Planes that contains members:", result)
>>>
>>>
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