[SR-10600] Runtime fails to demangle superclass when superclass's generic constraints are satisified in a conditional conformance

[swift-ci]

Previous ID	SR-10600
Radar	rdar://problem/50057445
Original Reporter	benpious (JIRA User)
Type	Bug

Attachment: Download

Environment

Xcode Version 10.2.1 (10E1001), running on the iOS simulator.

Additional Detail from JIRA

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

md5: e58a0fb9941799cfe7a5f7a11b213366

relates to:

• SR-10721 Runtime fails to demangle superclass when a type used to satisfy the superclass's generic bound is used in a superficial way

Issue Description:

Firstly, to address the elephant in the room, I know that this is the exact same error message as a crash that's already a known issue according to the Xcode 10.2 release notes. But based on my conversation with @jckarter on Twitter it's not clear if it's the same crash, hence this ticket.

TL:DR is that if you have a class C<T: P>, class D<T2> conforms to P if T2 conforms to P2, and class C2: C<D>, then C2's superclass metadata will be corrupted somehow.

See the sample project's SwiftTest2.swift file for an implementation of this.

[jckarter]

Thanks for narrowing down the reproducer!

[jckarter]

Looks like @DougGregor fixed this in the Swift 5.1 runtime in #24759 To backward deploy the fix to Swift 5.0 runtimes in existing OSes, here's a PR that exercises our runtime compatibility hooks: #25030

[swift-ci]

Comment by Helge Heß (JIRA)

public protocol Nice {
associatedtype Blub : Nice
var awesomeStuff : Self.Blub { get }
}

struct TestNice : Nice {
var awesomeStuff: some Nice { TestNice() }
}

func call<N: Nice>(for n: N) {
_ = n.awesomeStuff
}

call(for: TestNice()) 

got this one, which produces

2019-06-06 16:09:28.407874+0200 TestDemangle[62667:17535861] failed to demangle witness for associated type 'Blub' in conformance 'TestDemangle.TestNice: Nice' from mangled name '\^A%\^A' 

And @jckarter says might be the same issue. Need to check.