[SR-7450] Conditional Conformances: Runtime crash when reference self type.

[swift-ci]

Previous ID	SR-7450
Radar	rdar://problem/37170296
Original Reporter	tarunon (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode Version 9.3 (9E145)
Apple Swift version 4.1 (swiftlang-902.0.48 clang-902.0.37.1)
Target: x86_64-apple-darwin17.5.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, ConditionalConformance, RunTimeCrash
Assignee	None
Priority	Medium

md5: 5a9372b126515a64965caf844fecb76b

Issue Description:

protocol DictionaryType {
    associatedtype Key
    associatedtype Value

}

protocol A: DictionaryType where Key == Value {
    static func foo()
}

extension A {
    static func foo() {
        print(type(of: self))
    }
}

extension Dictionary: DictionaryType {}

extension Dictionary: A where Key == Value {
    
}

extension Array where Element: A {
    static func foo() {
        Element.foo()
    }
}

[String: String].foo() // Dictionary<String, String>
[[String: String]].foo() // Crash

1. Make protocol that extends other protocol equivement 2 associatedtypes.
2. Implement 2 protocols at 1 generics type.
3. Reference type in other generics extension function.

Maybe same bug of https://bugs.swift.org/browse/SR-7449

[belkadan]

@jckarter, @DougGregor, we were just talking about the possibility of something like this yesterday, right?

[jckarter]

Yeah, this looks like it could be what we're tracking as rdar://problem/37170296 internally. Our type-by-mangled-name runtime code doesn't yet handle all same-type-constrained contexts.

[DougGregor]

Yes, this is precisely what @jckarter was working on yesterday. I suspect that it'll be fixed by #15960

[jckarter]

That fix alone might not address this problem, since it doesn't include the runtime work to demangle types in contexts with same-type constraints.

[slavapestov]

Doug merged #19571 to master already