[SR-12133] Code compatibility regression in Swift 5.2 when using a type named "`Self`"

[JaviSoto]

Previous ID	SR-12133
Radar	rdar://problem/59216636
Original Reporter	@JaviSoto
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 11.4 Beta 1 in Swift 5 mode

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: aaf8d75237edc83c5ece6de2caeb53e9

Issue Description:

See the following code:

struct OuterType {
    struct `Self` {
        let string: String  
    }
    
    var foo: `Self`? {
        let optional: String? = "foo"
        return optional.map { `Self`(string: $0) }
    }
}

Untitled 3.swift:10:29: error: cannot convert value of type 'OuterType.`Self`' to closure result type 'OuterType?'
return optional.flatMap
Unknown macro: { `Self`(string}
^~~~~~~~~~~~~~~~~~

This compiles with Swift 5.1. The var declaration understands what type we're referring to (the nested `Self` type), but the closure code thinks that we're instantiating `Self` (aka `OuterType`)

If we change the code in the var to this, it compiles, even though it shouldn't:

var foo: `Self`? {
    // This shouldn't compile, because `self` is the wrong type.
    return self
}

[beccadax]

@swift-ci create

[JaviSoto]

Can we expect this to be fixed when 5.2 is out of beta in Xcode 11.4, since it's code that compiled previously?

Would like to plan whether we'll need to workaround this some other way, since this is generated code by the Apollo-iOS library (https://github.com/apollographql/apollo-ios) cc designatednerd (JIRA User)

[slavapestov]

I have a fix: #29900

[JaviSoto]

THANK YOU!! �

[JaviSoto]

I can confirm this is fixed in Xcode 11.4 Beta 3. Thanks everyone!