[SR-12428] Can't demangle Self

[krzyzanowskim]

Previous ID	SR-12428
Radar	rdar://problem/62200992
Original Reporter	@krzyzanowskim
Type	Bug

Environment

Apple Swift version 5.2 (swiftlang-1103.0.32.1 clang-1103.0.32.29)
Target: x86_64-apple-darwin19.4.0

Additional Detail from JIRA

Votes	1
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: 2018afc6624a7ec84ffd38dc809a25d5

Issue Description:

This code crashes in runtime at the line where `Self` is used:

class Foo: NSObject {
  @objc let value: String = "test"
  
  func test() {
    let k1 = \Foo.value  // Ok
    let k2 = \Self.value // Fatal error: could not demangle keypath type from '��: file /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-1103.8.25.8/swift/stdlib/public/core/KeyPath.swift, line 2623
  }
}

Foo().test()

https://gist.github.com/krzyzanowskim/2f2dd423ab59ca7a05dfa98a24a730d7

[beccadax]

@swift-ci create

[iharandreyev]

Have the same issue when working with classes. The class/property shouldn't necessarily be exposed to objc.

class FloatObject {
    var property: Float!

    func test() {
        let k1 = \FloatObject.property // OK
        let k2 = \Self.property // Fatal error: could not demangle keypath type from '�����XD'
    }
}

FloatObject().test()

Same with generics

class GenericObject<Property> {
    var property: Property!

    func test() {
        let k1 = \GenericObject<Property>.property // OK
        let k2 = \Self.property // Fatal error: could not demangle keypath type from '�[���yxGXD'
    }
}

GenericObject<Float>().test()

Structs work fine though

struct FloatStruct {
    var property: Float!

    func test() {
        let k = \Self.property // OK
        print(k)
    }
}

FloatStruct().test()

Generic structs work as well

struct GenericStruct<Property> {
    var property: Property!

    func test() {
        let k = \Self.property // OK
        print(k)
    }
}

GenericStruct<Float>().test()

[AnthonyLatsis]

Now crashes in the SIL verifier: SIL verification failed: can't upcast to same type.

[MFranceschi6]

Hi hello we have experienced the same issue without a crash from the compiler.

Swift version
Swift version 5.7 (swift-5.7-RELEASE)
Target: x86_64-unknown-linux-gnu

This is a snippet that causes the runtime fatalerror but not the compiler time crash

class Test {
    @TestWrapper var test: String = "test"

    func foo() {
        let k1 = \Test.$test
        let k2 = \Self.$test
    }
}

@propertyWrapper
class TestWrapper<Value> {

    var projectedValue: TestWrapper<Value> { self }

    var wrappedValue: Value
    
    init(wrappedValue: Value) {
        self.wrappedValue = wrappedValue
    }
}