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[SR-10713] The dynamic nature of a protocol's Self type isn't checked when equated with another associated type #53110
Description
| Previous ID | SR-10713 |
| Radar | None |
| Original Reporter | @hamishknight |
| Type | Bug |
| Status | Closed |
| Resolution | Done |
Environment
Swift version 5.1-dev (LLVM 082dec2e22, Swift 397965d3fc)
Target: x86_64-apple-darwin18.5.0
Additional Detail from JIRA
| Votes | 0 |
| Component/s | Compiler |
| Labels | Bug, AcceptsInvalid, TypeChecker |
| Assignee | @slavapestov |
| Priority | Medium |
md5: 68e52fe5d63fd695a13a186f306cb4bc
Issue Description:
The following unsound code is allowed to compile, which lets us turn a subclass instance into a superclass instance:
protocol P {
associatedtype X where X == Self
func foo() -> X
}
class C : P {
typealias X = C
func foo() -> X {
return C()
}
}
class D : C {}
func foo<T : P>(_ x: inout T) {
x = x.foo()
}
var d = D()
foo(&d)
print(type(of: d)) // CWhen checking the constraint X == Self, we should treat Self as being the dynamic self and therefore reject the conformance.
Activity
belkadan commentedon May 20, 2019
cc @slavapestov, @DougGregor
slavapestov commentedon May 20, 2019
Ouch!
slavapestov commentedon May 20, 2019
I think the only safe thing to do here is to not allow a class to conform to P at all.
belkadan commentedon May 20, 2019
Or only
finalclasses, or something.slavapestov commentedon Feb 25, 2022
#41545