Attachment: Download

duplicates:

• SR-6468 inheriting from class with synthesized Codable implementation creates invalid code

relates to:

• SR-7090 Crashing with EXC_BAD_ACCESS after decoding Codable subclass

Issue Description:

The compiler is able to synthesize Encodable conformance for certain types, including classes. However, something about the synthesized encode(to: ) method isn't right; it results in vtable lookup corruption when such classes are accessed from another source file:

a.swift:

class Base: Encodable {}

class Derived: Base {
  var derived10: Int { return 10 }
  var derived20: Int { return 20 }
}

main.swift:

let d = Derived()
print("d.derived20 == \(d.derived20)") // Prints 10 (expected: 20)
print("d.derived10 == \(d.derived10)") // crash (expected: 10)

Try:

$ swiftc a.swift main.swift 
$ ./main
d.derived20 == 10
Segmentation fault: 11

Apparently main.swift and a.swift disagree about the existence of the encode method in Derived's vtable, which makes the Derived class unusable.