Swift fails to link Array extension defined in framework

Originator:jlieske
Number:rdar://17500497 Date Originated:29-Jun-2014 04:55 PM
Status:Open Resolved:
Product:Developer Tools Product Version:Xcode6 beta: Version 6.0 (6A216f)
Classification:Other Bug Reproducible:Always
 
The Swift language supports extending standard library types with additional methods.  Such extensions should be exportable from modules/frameworks.  However, the Beta2 compiler either crashes or has a linkage error when attempting to use such an extension.  

For example, this is an extension on Array:

extension Array {
    var lastObject: T? { get {
        let n = self.count
        if n > 0 {
            return self[n-1]
        }
        else {
            return nil
        }
    }}
}

1. If that extension is defined in a framework module, code in the main application compiles but does not link:

Undefined symbols for architecture x86_64:
  "__TFSag10lastObjectGSqQ_", referenced from:
      __TFC12PlaySwiftApp11AppDelegate11applicationfS0_FTCSo13UIApplication29didFinishLaunchingWithOptionsGSqCSo12NSDictionary__Sb in AppDelegate.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

2. If that extension is defined in a framework module, code in the accompanying test module causes a compiler error:

0  swift                    0x000000010fa84e08 llvm::sys::PrintStackTrace(__sFILE*) + 40
1  swift                    0x000000010fa852f4 SignalHandler(int) + 452
2  libsystem_platform.dylib 0x00007fff8c67b5aa _sigtramp + 26
3  libsystem_platform.dylib 0x00007fff00000002 _sigtramp + 1939360370
4  swift                    0x000000010ee93cc7 emitNominalMetadataRef(swift::irgen::IRGenFunction&, swift::NominalTypeDecl*, swift::CanType) + 599
5  swift                    0x000000010ee829fc llvm::Value* swift::CanTypeVisitor<(anonymous namespace)::EmitTypeMetadataRef, llvm::Value*>::visit<>(swift::CanType) + 124
6  swift                    0x000000010ee82975 swift::irgen::IRGenFunction::emitTypeMetadataRef(swift::CanType) + 21
7  swift                    0x000000010eea59f9 swift::irgen::WitnessSizedTypeInfo<(anonymous namespace)::NonFixedEnumTypeInfo>::allocateStack(swift::irgen::IRGenFunction&, swift::CanType, llvm::Twine const&) const + 89
8  swift                    0x000000010eef2782 swift::SILVisitor<(anonymous namespace)::IRGenSILFunction, void>::visit(swift::ValueBase*) + 34626
9  swift                    0x000000010eee9846 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 8678
10 swift                    0x000000010ee6acd8 swift::irgen::IRGenModule::emitGlobalTopLevel() + 184
11 swift                    0x000000010eed6cc3 performIRGeneration(swift::IRGenOptions&, swift::Module*, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&, swift::SourceFile*, unsigned int) + 1859
12 swift                    0x000000010eed7613 swift::performIRGeneration(swift::IRGenOptions&, swift::SourceFile&, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&, unsigned int) + 51
13 swift                    0x000000010ee4995a frontend_main(llvm::ArrayRef<char const*>, char const*, void*) + 4842
14 swift                    0x000000010ee4865d main + 1533
15 libdyld.dylib            0x00007fff947d05fd start + 1
Stack dump:

1.	While emitting IR SIL function @_TFC14PlaySwiftTests13JaySwiftTests19testArrayLastObjectfS0_FT_T_ for 'testArrayLastObject' at JaySwiftTests.swift:14:5
<unknown>:0: error: unable to execute command: Segmentation fault: 11
<unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)
Command /Applications/Xcode6-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift failed with exit code 254

Comments

The problem still exists Xcode 6.3, though the error message changed after the betas. Declaring an extension like the following:

public extension Array { public var myLastObject: T? { get { let n = self.count if n > 0 { return self[n-1] } else { return nil } } } }

Xcode 6.2 and 6.3 beta 2 report the following error:

/Users/jay/Coding/Swift/TrySwift/TryFramework/TryArrayExtension.swift:12:16: Extension of generic type 'Array' from a different module cannot provide public declarations

By jlieske at March 7, 2015, 6:05 a.m. (reply...)

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