Runtime crash when compiling with Swift 6 and running on Swift 5.X runtime

[MarkVillacampa]

Description

Using the version of Swift 6 bundled with Xcode 16 beta 1, the following two snippets of code compile and run fine in iOS 18 (sim/device) and macOS 15, but crash when run in iOS 17 (sim/device) and macOS 14.

Filing as the same issue as I believe they can be related. If not, please let me know and I'll open separate issues.

UPDATE: I wanted to see if this was an issue only with the build of Swift bundled with Xcode 16 beta 1, so I installed the newest and the oldest snapshots of the release/6.0 train from https://www.swift.org/install/macos/ and ran code with Xcode 15.4, confirming the same crash is present in both.

Oldest: Swift 6.0 Development Snapshot 2024-04-29 (a)
Newest: Swift 6.0 Development Snapshot 2024-06-11 (a)

Reproduction

Snippet 1:

import Foundation
protocol TestProtocol {}
extension Optional: TestProtocol {}
struct TestGenericStruct<GenericType: TestProtocol> {
    var foo: Date?
}
_ = TestGenericStruct<Date?>(foo: Date())

Snippet 2:

import Foundation
protocol TestProtocol {}
@propertyWrapper
struct TestPropertyWrapper<GenericType: TestProtocol>: Codable {
    var wrappedValue: String = ""
}
extension Optional: TestProtocol {}
struct TestStruct: Codable {
    @TestPropertyWrapper<String?>
    var foo: String
}
_ = try JSONEncoder().encode(TestStruct(foo: .init(wrappedValue: "")))

Stack dump

Snippet 1:

crash`main:
    0x100001918 <+0>:   stp    x29, x30, [sp, #-0x10]!
    0x10000191c <+4>:   mov    x29, sp
    0x100001920 <+8>:   sub    sp, sp, #0x30
    0x100001924 <+12>:  adrp   x0, 7
    0x100001928 <+16>:  add    x0, x0, #0x0 ; demangling cache variable for type metadata for Swift.Optional<Foundation.Date>
    0x10000192c <+20>:  bl     0x100001a10    ; __swift_instantiateConcreteTypeFromMangledName at <compiler-generated>
    0x100001930 <+24>:  stur   x0, [x29, #-0x18]
    0x100001934 <+28>:  ldur   x8, [x0, #-0x8]
    0x100001938 <+32>:  ldr    x8, [x8, #0x40]
    0x10000193c <+36>:  lsr    x8, x8, #0
    0x100001940 <+40>:  add    x8, x8, #0xf
    0x100001944 <+44>:  and    x9, x8, #0xfffffffffffffff0
    0x100001948 <+48>:  stur   x9, [x29, #-0x30]
    0x10000194c <+52>:  adrp   x16, 3
    0x100001950 <+56>:  ldr    x16, [x16]
    0x100001954 <+60>:  blr    x16
    0x100001958 <+64>:  ldur   x9, [x29, #-0x30]
    0x10000195c <+68>:  mov    x8, sp
    0x100001960 <+72>:  subs   x0, x8, x9
    0x100001964 <+76>:  stur   x0, [x29, #-0x20]
    0x100001968 <+80>:  mov    sp, x0
    0x10000196c <+84>:  adrp   x0, 7
    0x100001970 <+88>:  add    x0, x0, #0x8 ; demangling cache variable for type metadata for crash.TestGenericStruct<Swift.Optional<Foundation.Date>>
    0x100001974 <+92>:  bl     0x100001a10    ; __swift_instantiateConcreteTypeFromMangledName at <compiler-generated>
    0x100001978 <+96>:  ldur   x8, [x29, #-0x20]
->  0x10000197c <+100>: ldur   x9, [x0, #-0x8]
    0x100001980 <+104>: ldr    x9, [x9, #0x40]
    0x100001984 <+108>: lsr    x9, x9, #0
    0x100001988 <+112>: add    x9, x9, #0xf
    0x10000198c <+116>: and    x9, x9, #0xfffffffffffffff0
    0x100001990 <+120>: stur   x9, [x29, #-0x28]
    0x100001994 <+124>: adrp   x16, 3
    0x100001998 <+128>: ldr    x16, [x16]
    0x10000199c <+132>: blr    x16
    0x1000019a0 <+136>: ldur   x10, [x29, #-0x28]
    0x1000019a4 <+140>: mov    x9, sp
    0x1000019a8 <+144>: subs   x0, x9, x10
    0x1000019ac <+148>: stur   x0, [x29, #-0x10]
    0x1000019b0 <+152>: mov    sp, x0
    0x1000019b4 <+156>: bl     0x100003994    ; symbol stub for: Foundation.Date.init() -> Foundation.Date
    0x1000019b8 <+160>: mov    x0, #0x0 ; =0
    0x1000019bc <+164>: bl     0x1000039a0    ; symbol stub for: type metadata accessor for Foundation.Date
    0x1000019c0 <+168>: mov    x3, x0
    0x1000019c4 <+172>: ldur   x0, [x29, #-0x20]
    0x1000019c8 <+176>: ldur   x8, [x3, #-0x8]
    0x1000019cc <+180>: ldr    x8, [x8, #0x38]
    0x1000019d0 <+184>: mov    w1, #0x0 ; =0
    0x1000019d4 <+188>: stur   w1, [x29, #-0x4]
    0x1000019d8 <+192>: mov    w2, #0x1 ; =1
    0x1000019dc <+196>: blr    x8
    0x1000019e0 <+200>: ldur   x0, [x29, #-0x20]
    0x1000019e4 <+204>: ldur   x1, [x29, #-0x18]
    0x1000019e8 <+208>: ldur   x8, [x29, #-0x10]
    0x1000019ec <+212>: adrp   x2, 3
    0x1000019f0 <+216>: add    x2, x2, #0x118 ; protocol witness table for Swift.Optional<τ_0_0> : crash.TestProtocol in crash
    0x1000019f4 <+220>: bl     0x100001a7c    ; crash.TestGenericStruct.init(foo: Swift.Optional<Foundation.Date>) -> crash.TestGenericStruct<GenericType> at crash.swift:4
    0x1000019f8 <+224>: ldur   x0, [x29, #-0x10]
    0x1000019fc <+228>: bl     0x100001aa8    ; outlined destroy of crash.TestGenericStruct<Swift.Optional<Foundation.Date>> at <compiler-generated>
    0x100001a00 <+232>: ldur   w0, [x29, #-0x4]
    0x100001a04 <+236>: mov    sp, x29
    0x100001a08 <+240>: ldp    x29, x30, [sp], #0x10
    0x100001a0c <+244>: ret

Snippet 2:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x000000019b6c3d50 libswiftCore.dylib`swift::TargetMetadata<swift::InProcess>::getTypeContextDescriptor() const + 4
    frame #1: 0x000000019b6c8588 libswiftCore.dylib`swift::TargetMetadata<swift::InProcess>::getGenericArgs() const + 24
    frame #2: 0x000000019b6feb38 libswiftCore.dylib`instantiateWitnessTable(swift::TargetMetadata<swift::InProcess> const*, swift::TargetProtocolConformanceDescriptor<swift::InProcess> const*, void const* const*, void**) + 260
    frame #3: 0x000000019b6f326c libswiftCore.dylib`swift::_getWitnessTable(swift::TargetProtocolConformanceDescriptor<swift::InProcess> const*, swift::TargetMetadata<swift::InProcess> const*, void const* const*) + 4704
    frame #4: 0x0000000100005d98 crash`lazy protocol witness table accessor for type TestPropertyWrapper<String?> and conformance TestPropertyWrapper<A> at <compiler-generated>:0
    frame #5: 0x0000000100005cb4 crash`TestStruct.encode() at <compiler-generated>:0
    frame #6: 0x000000010000621c crash`protocol witness for Encodable.encode(to:) in conformance TestStruct at <compiler-generated>:0
    frame #7: 0x000000019b694fa0 libswiftCore.dylib`dispatch thunk of Swift.Encodable.encode(to: Swift.Encoder) throws -> () + 32
    frame #8: 0x000000018ca86e38 Foundation`generic partial specialization <Signature = @escaping @convention(thin) <τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1 == Foundation._JSONKey> (@guaranteed Foundation.__JSONEncoder, @in_guaranteed τ_0_0) -> (@error @owned Swift.Error)> of closure #1 (Foundation.__JSONEncoder) throws -> () in Foundation.__JSONEncoder.wrapGeneric<τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1: Swift.CodingKey>(_: τ_0_0, for: Foundation._JSONCodingPathNode, _: Swift.Optional<τ_0_1>) throws -> Swift.Optional<Foundation.JSONReference> + 148
    frame #9: 0x000000018ca8aacc Foundation`partial apply forwarder for generic partial specialization <Signature = @escaping @convention(thin) <τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1 == Foundation._JSONKey> (@guaranteed Foundation.__JSONEncoder, @in_guaranteed τ_0_0) -> (@error @owned Swift.Error)> of closure #1 (Foundation.__JSONEncoder) throws -> () in Foundation.__JSONEncoder.wrapGeneric<τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1: Swift.CodingKey>(_: τ_0_0, for: Foundation._JSONCodingPathNode, _: Swift.Optional<τ_0_1>) throws -> Swift.Optional<Foundation.JSONReference> + 24
    frame #10: 0x000000018ca8703c Foundation`generic specialization <Foundation._JSONKey> of Foundation.__JSONEncoder._wrapGeneric<τ_0_0 where τ_0_0: Swift.CodingKey>(_: (Foundation.__JSONEncoder) throws -> (), for: Foundation._JSONCodingPathNode, _: Swift.Optional<τ_0_0>) throws -> Swift.Optional<Foundation.JSONReference> + 288
    frame #11: 0x000000018ca7a0c0 Foundation`generic partial specialization <Signature = @escaping @convention(thin) @convention(method) <τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1 == Foundation._JSONKey> (@in_guaranteed τ_0_0, @guaranteed Foundation._JSONCodingPathNode, @guaranteed Swift.Optional<Foundation._JSONKey>, @guaranteed Foundation.__JSONEncoder) -> (@owned Swift.Optional<Foundation.JSONReference>, @error @owned Swift.Error)> of Foundation.__JSONEncoder.wrapGeneric<τ_0_0, τ_0_1 where τ_0_0: Swift.Encodable, τ_0_1: Swift.CodingKey>(_: τ_0_0, for: Foundation._JSONCodingPathNode, _: Swift.Optional<τ_0_1>) throws -> Swift.Optional<Foundation.JSONReference> + 2048
    frame #12: 0x000000018ca792a4 Foundation`Foundation.JSONEncoder.encode<τ_0_0 where τ_0_0: Swift.Encodable>(τ_0_0) throws -> Foundation.Data + 456
    frame #13: 0x000000018ca89240 Foundation`dispatch thunk of Foundation.JSONEncoder.encode<τ_0_0 where τ_0_0: Swift.Encodable>(τ_0_0) throws -> Foundation.Data + 56
    frame #14: 0x00000001000048fc crash`main at crash.swift:12:23
    frame #15: 0x000000018b2de0e0 dyld`start + 2360
(lldb) dis
libswiftCore.dylib`swift::TargetMetadata<swift::InProcess>::getTypeContextDescriptor:
    0x19b6c3d4c <+0>:   mov    x16, #0x0 ; =0
->  0x19b6c3d50 <+4>:   ldr    x8, [x0]
    0x19b6c3d54 <+8>:   cmp    x8, #0x7ff
    0x19b6c3d58 <+12>:  csel   w8, wzr, w8, hi
    0x19b6c3d5c <+16>:  cmp    w8, #0x202
    0x19b6c3d60 <+20>:  b.gt   0x19b6c3dac    ; <+96>
    0x19b6c3d64 <+24>:  sub    w9, w8, #0x200
    0x19b6c3d68 <+28>:  cmp    w9, #0x3
    0x19b6c3d6c <+32>:  b.hs   0x19b6c3dc8    ; <+124>
    0x19b6c3d70 <+36>:  ldr    x8, [x0, #0x8]!
    0x19b6c3d74 <+40>:  cbz    x8, 0x19b6c3e48 ; <+252>
    0x19b6c3d78 <+44>:  mov    x16, x8
    0x19b6c3d7c <+48>:  mov    x17, x0
    0x19b6c3d80 <+52>:  movk   x17, #0xae86, lsl #48
    0x19b6c3d84 <+56>:  autda  x16, x17
    0x19b6c3d88 <+60>:  mov    x17, x16
    0x19b6c3d8c <+64>:  xpacd  x17
    0x19b6c3d90 <+68>:  cmp    x16, x17
    0x19b6c3d94 <+72>:  b.eq   0x19b6c3d9c    ; <+80>
    0x19b6c3d98 <+76>:  brk    #0xc472
    0x19b6c3d9c <+80>:  mov    x17, #0x85c2 ; =34242
    0x19b6c3da0 <+84>:  pacdb  x16, x17
    0x19b6c3da4 <+88>:  cbnz   x16, 0x19b6c3e0c ; <+192>
    0x19b6c3da8 <+92>:  b      0x19b6c3e40    ; <+244>
    0x19b6c3dac <+96>:  cmp    w8, #0x203
    0x19b6c3db0 <+100>: b.eq   0x19b6c3dbc    ; <+112>
    0x19b6c3db4 <+104>: cmp    w8, #0x204
    0x19b6c3db8 <+108>: b.ne   0x19b6c3e40    ; <+244>
    0x19b6c3dbc <+112>: ldr    x8, [x0, #0x8]!
    0x19b6c3dc0 <+116>: cbnz   x8, 0x19b6c3ddc ; <+144>
    0x19b6c3dc4 <+120>: b      0x19b6c3e48    ; <+252>
    0x19b6c3dc8 <+124>: cbnz   w8, 0x19b6c3e40 ; <+244>
    0x19b6c3dcc <+128>: ldrb   w8, [x0, #0x20]
    0x19b6c3dd0 <+132>: tbz    w8, #0x1, 0x19b6c3e48 ; <+252>
    0x19b6c3dd4 <+136>: ldr    x8, [x0, #0x40]!
    0x19b6c3dd8 <+140>: cbz    x8, 0x19b6c3e48 ; <+252>
    0x19b6c3ddc <+144>: mov    x16, x8
    0x19b6c3de0 <+148>: mov    x17, x0
    0x19b6c3de4 <+152>: movk   x17, #0xae86, lsl #48
    0x19b6c3de8 <+156>: autda  x16, x17
    0x19b6c3dec <+160>: mov    x17, x16
    0x19b6c3df0 <+164>: xpacd  x17
    0x19b6c3df4 <+168>: cmp    x16, x17
    0x19b6c3df8 <+172>: b.eq   0x19b6c3e00    ; <+180>
    0x19b6c3dfc <+176>: brk    #0xc472
    0x19b6c3e00 <+180>: mov    x17, #0xfd78 ; =64888
    0x19b6c3e04 <+184>: pacdb  x16, x17
    0x19b6c3e08 <+188>: cbz    x16, 0x19b6c3e40 ; <+244>
    0x19b6c3e0c <+192>: mov    x16, x8
    0x19b6c3e10 <+196>: mov    x17, x0
    0x19b6c3e14 <+200>: movk   x17, #0xae86, lsl #48
    0x19b6c3e18 <+204>: autda  x16, x17
    0x19b6c3e1c <+208>: mov    x17, x16
    0x19b6c3e20 <+212>: xpacd  x17
    0x19b6c3e24 <+216>: cmp    x16, x17
    0x19b6c3e28 <+220>: b.eq   0x19b6c3e30    ; <+228>
    0x19b6c3e2c <+224>: brk    #0xc472
    0x19b6c3e30 <+228>: mov    x17, #0xf445 ; =62533
    0x19b6c3e34 <+232>: pacdb  x16, x17
    0x19b6c3e38 <+236>: mov    x0, x16
    0x19b6c3e3c <+240>: ret
    0x19b6c3e40 <+244>: mov    x0, x16
    0x19b6c3e44 <+248>: ret
    0x19b6c3e48 <+252>: mov    x0, #0x0 ; =0
    0x19b6c3e4c <+256>: ret
(lldb)

Expected behavior

Code runs normally without crashing like when compiling with Swift 5.

Environment

Xcode 16 beta 1 (16A5171c)

swift-driver version: 1.109.2 Apple Swift version 6.0 (swiftlang-6.0.0.3.300 clang-1600.0.20.10)
Target: arm64-apple-macosx14.0

ProductName: macOS
ProductVersion: 14.5
BuildVersion: 23F79

Additional information

run with: swiftc -g -Onone crash.swift -o crash && lldb crash -o run

[NachoSoto]

Still reproducing on beta 2.

[MarkVillacampa]

This seems to be fixed by #74604

Can no longer reproduce using the latest release/6.0 build (June 22, 2024) from https://www.swift.org/install/macos/

[rwov]

This seems to be fixed by #74604

Can no longer reproduce using the latest release/6.0 build (June 22, 2024) from https://www.swift.org/install/macos/

will installing 6.0 with the link update Xcode accordingly?