[SR-11636] Accessing covariant `Self` from stored property initializer in extension segfaults

[DeFrenZ]

Previous ID	SR-11636
Radar	rdar://problem/56467142
Original Reporter	@DeFrenZ
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 11.1 (11A1027)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, CompilerCrash, StarterBug
Assignee	@CodaFi
Priority	Medium

md5: 95fa6dd3261c88c421192579e14d986d

is duplicated by:

• SR-11689 Segmentation fault referring to Self in class extension

Issue Description:

This crashes the compiler

class Foo {}
extension Foo {
    static let foo = "\(Self.self)"
}

Doing the same but without the extension gives the correct (I believe) error

[belkadan]

@slavapestov, think this would be a good starter bug?

[belkadan]

@swift-ci create

[slavapestov]

Yes, the fact that we correctly diagnose a class member but crash on an extension member suggests that this is a matter if tracking down an incorrect `isa<>` check. Definitely a good starter bug candidate.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

I'd like to fix this problem. Where should I start? @slavapestov

[theblixguy]

The error is emitted by TypeChecker::checkPatternBindingCaptures, so perhaps you can start from there. It doesn't seem like it's called for a ExtensionDecl, so one way to fix it would be to change checkPatternBindingCaptures to accept a IterableDeclContext rather than a NominalTypeDecl and then calling TypeChecker::checkPatternBindingCaptures(ED) in visitExtensionDecl in TypeCheckDecl.cpp.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

It seems that the duplicated issue SR-11689 has been fixed. Also I'v tested with the latest Swift code and it works fine. So I think this issue should be closed too.

[slavapestov]

ninjiacoder (JIRA User) The bug is definitely still present in the latest master. @theblixguy's explanation for how to fix the problem is the correct one. Let me know if you still want to attempt this.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

@slavapestov Sure. I still want to fix it.

[CodaFi]

ninjiacoder (JIRA User) Sorry, I took this one over on #28392 We got an unrelated bug report and I didn't see this issue already had somebody assigned...

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

@CodaFi Never mind. Glad to hear that it's fixed! 🙂

[CodaFi]

Resolved by the merge of #28392