[SR-11642] Runtime crash demangling associated type for type defined in equality-constrained extension

[swift-ci]

Previous ID	SR-11642
Radar	rdar://problem/56466693
Original Reporter	siemensikkema (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

macOS Catalina

MacBook Pro (15-inch, 2017)

Xcode 11 Version 11.1 (11A1027)

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug, Generics, RunTimeCrash, Runtime
Assignee	None
Priority	Medium

md5: 5e3272992c6dde352a1ca1e2e8d25287

Issue Description:

I found a runtime crash when running the following code (e.g. in a playground):

// MARK: Types


struct Validator<T> {
    let validatorFailureType: Any.Type
}


protocol ValidatorType {
    associatedtype Data
    associatedtype Failure
    func validator() -> Validator<Data>
}


extension ValidatorType {
    func validator() -> Validator<Data> {
        .init(validatorFailureType: Failure.self)
    }
}


// MARK: Failing example


extension Validator where T == String {
    struct V: ValidatorType {
        typealias Data = T // or String
        struct Failure {}
    }
}


Validator.V().validator() // failed to demangle witness for associated type 'Failure' in conformance '(extension in __lldb_expr_1):__lldb_expr_1.Validator<Swift.String>.V4: ValidatorType' from mangled name '13__lldb_expr_19ValidatorVAASSRszrlE2V4V7FailureVyx__G'

I attached a playground file that contains a few similar but non-crashing examples.

[belkadan]

Looks similar to some of the other same-type-constraint issues we've seen…

@swift-ci create

[DougGregor]

Fixed by #28869