Open Radar

 
Summary:
In the attached example calling "test()" dynamically on the base class causes an EXC_BAD_ACCESS at runtime.

It worked fine in Swift 1.

Steps to Reproduce:
1. Copy the attached code into a Playground.
2. Run the code in the playground.


Expected Results:
Program should complete without any problems.

Actual Results:
Playground execution failed: Execution was interrupted, reason: EXC_BAD_ACCESS (code=1, address=0xfffffffffffffff8).
* thread #1: tid = 0xb8cd, 0x0000000109cd5750 libswiftCore.dylib`swift_initEnumValueWitnessTableSinglePayload + 16, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0xfffffffffffffff8)
  * frame #0: 0x0000000109cd5750 libswiftCore.dylib`swift_initEnumValueWitnessTableSinglePayload + 16
    frame #1: 0x0000000109c4c2fb libswiftCore.dylib`___lldb_unnamed_function447$$libswiftCore.dylib + 43
    frame #2: 0x0000000109ccefa8 libswiftCore.dylib`(anonymous namespace)::GenericCacheEntry* llvm::function_ref<(anonymous namespace)::GenericCacheEntry* ()>::callback_fn<swift::swift_getGenericMetadata::$_0>(long) + 24
    frame #3: 0x0000000109cceeb0 libswiftCore.dylib`MetadataCache<(anonymous namespace)::GenericCacheEntry>::addMetadataEntry(EntryRef<(anonymous namespace)::GenericCacheEntry>, ConcurrentList<MetadataCache<(anonymous namespace)::GenericCacheEntry>::EntryPair>&, llvm::function_ref<(anonymous namespace)::GenericCacheEntry* ()>) + 128
    frame #4: 0x0000000109ccb698 libswiftCore.dylib`swift_getGenericMetadata + 504
    frame #5: 0x0000000109ccb6e5 libswiftCore.dylib`swift_getGenericMetadata1 + 21
    frame #6: 0x00000001123e67cb $__lldb_expr93`__lldb_expr_93.ChildClass.test <A where A: __lldb_expr_93.OtherBaseClass> (self=0x00000001123f2040)() -> Swift.Optional<A> + 187 at MyPlayground.playground:18
    frame #7: 0x00000001123e61ff $__lldb_expr93`main + 511 at MyPlayground.playground:24
    frame #8: 0x000000010789cc00 MyPlayground
    frame #9: 0x00000001078a0301 MyPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 17
    frame #10: 0x000000010789f631 MyPlayground`partial apply forwarder for reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 81
    frame #11: 0x00000001078a0330 MyPlayground`reabstraction thunk helper from @callee_owned (@in ()) -> (@out ()) to @callee_owned () -> (@unowned ()) + 32
    frame #12: 0x00000001078a0367 MyPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_unowned @convention(block) () -> (@unowned ()) + 39
    frame #13: 0x0000000107eb976c CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
    frame #14: 0x0000000107eaf2d5 CoreFoundation`__CFRunLoopDoBlocks + 341
    frame #15: 0x0000000107eaea32 CoreFoundation`__CFRunLoopRun + 850
    frame #16: 0x0000000107eae458 CoreFoundation`CFRunLoopRunSpecific + 488
    frame #17: 0x000000010ea7cbca GraphicsServices`GSEventRunModal + 161
    frame #18: 0x000000010833a1c2 UIKit`UIApplicationMain + 171
    frame #19: 0x000000010789d049 MyPlayground`main + 1097
    frame #20: 0x000000010ae1992d libdyld.dylib`start + 1


Attached file:

import Foundation

public class OtherBaseClass {}
public class OtherChildClass: OtherBaseClass {}


class BaseClass {

	func test<T: OtherBaseClass>() -> T? {
		fatalError()
	}
}


final class ChildClass<T: OtherBaseClass> : BaseClass {

	override func test() -> T? {
		return nil
	}
}


let instance: BaseClass = ChildClass<OtherChildClass>()
instance.test()