[SR-14797] Typealiases defined in protocols cannot be used as property wrappers

[matt-curtis]

Previous ID	SR-14797
Radar	rdar://problem/79563721
Original Reporter	@matt-curtis
Type	Bug

Environment

Swift 5.5

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | Compiler | |Labels | Bug | |Assignee | None | |Priority | Medium | md5: 6820bee8f850c8066494428a3379417c

Issue Description:

Here's some sample code that shows an instance where this issue appears:

@propertyWrapper
struct PropertyWrapper<Wrapped> { var wrappedValue: Wrapped }

protocol SomeProtocol {

    typealias SpecializedPropertyWrapper<Wrapped> = PropertyWrapper<Wrapped>

}

struct SomeConformingType: SomeProtocol { }

struct AStruct {

    @SomeConformingType.SpecializedPropertyWrapper var string: String // unknown attribute 'SomeConformingType.SpecializedPropertyWrapper'

}

There's also a discussion on the Swift forums spawned by this issue.

[typesanitizer]

@swift-ci create