[SR-27] Passing variadic function as a function parameter crashes compiler with SIGSEGV about swift HOT 3 CLOSED

Comment by Nikita Leonov (JIRA)

I had the same issue reported as radar, and duplicated it here as well SR-41. Sorry for duplication, as I didn't expect this issue to be so popular and already reported by someone else. Apparently there was one already reported.

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Comment by Steven Downum (JIRA)

This is probably not unexpected considering the nature of the issue, but I was able to yield a very similar result under Ubuntu 14.04:

  6> func variadic(numbers: Int...) {}
  7> [1].forEach(variadic)
lldb: /home/buildslave/jenkins/workspace/oss-swift-linux-packages-ubuntu_14_04-one-off-build/swift/lib/SILGen/SILGenExpr.cpp:1799: void emitTupleShuffleExprInto((anonymous namespace)::RValueEmitter &, swift::TupleShuffleExpr *, swift::Lowering::Initialization *): Assertion `innerMapping >= 0 && "non-argument tuple shuffle with default arguments or variadics?"' failed.
Aborted

I can add to SR-41, if desired.

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This one is resolved in master by the type error.

Variadics are a distinct type from "ground types". If you want to pass them around, you have to explicitly annotate the function as accepting that kind of type. Swift's type system does not support arity-generic overloads like you suspect it should here (though this may be something you could go through the evolution process to ask for if you think it is a useful feature). If you need to invoke these variadic functions, you must explicitly apply the necessary number of arguments. For example:

func giveMeVoid(callback: (Void)->Void) {
  
}

func giveMeInt(callback: (Int)->Void) {
  
}

func any(values:Any?...) {
  
}

any()
any(values: 5)

giveMeVoid { any() }
giveMeInt { any(values: $0) } 

If you need to pass these functions, then you can annotate the types of each function as accepting a variadic number of arguments and we'll figure out the rest for you (but you must maintain invariance [as though they were an [Blah] instead of Blah...])

func giveMeInt(callback: (Int...)->Void) {
  
}

func any(values:Int...) {
  
}

giveMeInt(any) 

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