[swift-users] Sporadically undefined symbols during linking

[Ryan Conway]

Daniel, thank you for taking the time to clone the repository and reproduce
the issue yourself.

I was a bit unclear in my last email. The 75% failure chance and 25%
success chance are strictly from clean builds. Once a build fails or
succeeds, it will continue to do so 100% of the time until a clean. (All of
this is assuming no source changes.) I have only experienced this one mode
of failure, as far as I can tell, and when builds succeed, the framework is
generated and code that uses it builds and runs as expected.

I've opened a bug at bugreporter.apple.com with ID 25511119 and clearer
information.

By the way - I didn't mention it in the ticket because I'm not confident it
has anything to do with this issue - but when building previous iterations
of this code with previous versions of Xcode that used Swift 2.1, I saw
reliable compilation failures in which the order of generic type
constraints' members mattered. That is, given the following two protocols:

protocol Foo { typealias Bar }
protocol Baz { typealias Buzz }

This would work:
struct MyGoodStruct<T: protocol<Baz, Foo> where T.Bar == T.Buzz, T.Bar:
IntegerType> {}

And this would not:
struct MyBadStruct<T: protocol<Baz, Foo> where T.Buzz == T.Bar, T.Bar:
IntegerType> {}

As far as I could tell, this had been fixed in Swift 2.2. I bring this up
only because these new linking failures seem to be related to
ostrichframework's Instruction protocol and its implementors.

Thanks again,
Ryan

On Sat, Apr 2, 2016 at 9:41 AM, Daniel Dunbar <daniel_dunbar at apple.com>
wrote:

> Are you saying that it fails about 75% of the time even when building from
> clean, or it fails overall 75% of the time and you have to build from clean
> to fix? In my experiments it always fails when building just
> ostrichframework. My guess is that if you build in the IDE you are seeing
> it sometimes stop based on one failure and other times stop based on
> another failure.
>
> Can you open a bug on bugreporter.apple.com about this (and let me know
> the #), I do see some surprising behavior on your project.
>
>  - Daniel
>
> On Apr 1, 2016, at 7:19 PM, Ryan Conway via swift-users <
> swift-users at swift.org> wrote:
>
> Hey swift-users,
>
> I'm experiencing a linking issue that causes builds to sometimes complete
> and sometimes fail, without code changes. I'm not sure if the problem is
> with Swift, Xcode, or my usage of either.
>
> My Xcode 7.3 project target is a Swift framework with no dependencies
> other than Foundation. Compiling always succeeds, but linking fails about
> 75% of the time with errors like the following:
>
> Undefined symbols for architecture x86_64:
> "__TWPuRx16ostrichframework11OperandTypexS_8ReadablexS_9WriteablewxPS1_8ReadTypezVs6UInt16wxPS2_9WriteTypezS4_ERRzS4_ERRzS4_ERRzSiERRzSiERRzSiERRzSirGVS_5DEC16x_S_11InstructionS_",
> referenced from:
>       ostrichframework.Z80.getInstruction () ->
> ostrichframework.Instruction? in Z80.o
> ld: symbol(s) not found for architecture x86_64
>
> The other 25% of the time, the framework will be built fine, with its user
> application working as expected.
>
> Has anyone experienced issues like this, or does anyone have advice on
> troubleshooting it? I've tried cleaning, deleting DerivedData, and building
> on a different machine, to no avail.
>
> If it helps, the failing project is "ostrichframework" found in the Xcode
> workspace here: https://github.com/PumpMagic/ostrich
>
> Any help is greatly appreciated.
>
> Ryan
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>
>
>
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